The Aquatic Amniote

Emerging New Research 1 – Recent Aquatic Amniote Literature Reviewed

2010-11-04T05:39:00.009-04:00

Now that I have gotten the news of the recent symposium out of the way, I’d like to present a new type of post for me – an annotated review of recent literature on aquatic amniotes and matters relevant to the study of their paleobiology. My intention with this is to highlight the primary utility I see in recently published work, including some curious details that seem often get ignored, and occasionally review an “oldie but goodie” from among the pieces of less-cited literature that I worry hasn’t gotten the recognition it deserves. I will do my best to be open and honest, but don’t want this to be a way of building a long list of enemies either, so if I do not nitpick every paper’s problems and instead focus on what strengths it has, I hope you’ll forgive me. If you are the author of one of these papers and feel I haven’t gotten the point of it, or misrepresented it in some way, I would really appreciate your comments on the blog, or a direct message to me. This is not meant as a critique of research, only a way of pointing out some recent work that might have been missed by the greater aquatic amniote paleontological community. The literature is vast and growing everyday, and I’d like to consider this an aspect of service to our community of scientists – I’m going to read these anyway, so I may as well save you all the trouble of finding these papers and get the news out.

Each of these will have a link to a journal site (or preferably a site at which the paper is available open access), so I hope that this will serve as an aid for all of you that haven’t the time to review all the literature. Though many of these papers I get directly from authors or through journal subscriptions, many of the papers I review I received thanks to the gracious efforts of David Janiger (LACM). David lists recent papers and offers pdfs to people on the MARMAM listserv (by the way, Academia.edu has a Marmam listserv section). If you already get papers thanks to his help, or are reading this blog, thank him already! He has been doing this for a while, and it is incredibly valuable.

Fourteen nuclear genes provide phylogenetic resolution for difficult nodes in the turtle tree of life.
Anthony J. Barley, Phillip Q. Spinks, Robert C. Thomson, H. Bradley Shaffer
Molecular Phylogenetics and Evolution 55:1189-1194

Bradley Shaffer Lab page
author's page for pdf

This short and sweet paper about a nuclear gene-based phylogeny of modern turtles nicely resolves some of the persistent problems of the relationships among turtle families, particularly due to the taxon Platysternon (big-headed turtle). The taxon sampling here isn’t extremely extensive (19), but it gets at least two taxa from each family of interest, particularly with respect to the Kinosternidae, Chelydridae, Emydidae, and Chelonioidea. As a start at getting a molecular phylogeny that can resolve these contentious relationships, this study does well. I found it particularly satisfying that kinosternids and chelydrids are sister taxa here, together as sister taxa to the Chelonioidea. Parham et al (2006) found similar, but not the same results, having these three clades not as a monophyletic group, but paraphyletic nested sister taxa to the Emydidae, Platysternon, Geomydidae, and Testudinidae (for more papers by Jim Parham related to this, visit his site). The taxon sampling of the present study is not extensive, so ultimately after many more taxa are sampled for these same genes and other molecular and morphological data, we may find this remains stable, or not. Either way, this has some interesting relevance to the origins of sea turtles, and the relative age of these clades.

Understanding the diet composition of marine mammals: grey seals (Halichoerus grypus) in the Baltic Sea).
Karl Lundström, Olle Hjerne, Sven-Gunnar Lunneryd, Olle Karlsson
ICES Journal of Marine Science 67:1230-1239

Author's Academia.edu page

The literature on the diets of marine mammals is huge, even though a concrete idea of exactly what animals eat (taxonomic diversity, abundance) and how this diet varies with age and distribution is a difficult matter to resolve. The best global look at this I know of is a paper more than 10 years old (Pauly et al 1998), even though copious reports on stomach contents exist. Large-scale studies are difficult to coordinate in this way because so much of the existing literature on diet is uneven in its quality and coverage, often sampling only strandings or not accounting for abundance or taxonomic diversity. Here, this group has done so for the grey seal, Halichoerus grypus, in the Baltic Sea. The divided their sample of hunted seal specimens (which they got in cooperation with hunters and fisheries sources) by regions of the Baltic and age categories. What I really love is their care for the data on abundance AND diversity of stomach AND intestinal contents, and that they report all their data, and even correct it for Erosion-class-specific size and numerical correction factors. As one might predict from the nature of biology, when they looked closely at these details, they found differences in the diets of young and old, and between regions. These differences seem largely to be concerned with commercially caught fishes, which is of practical importance, but one could easily envision using this same data to compare paleodietary measures of the same specimens (isotopes, dental microwear, etc.). Gosh, I need to contact some people in Sweden!

Mid-Cenomanian vertebrate faunas of the Western Interior Seaway of North America and their evolutionary, paleobiogeographical, and paleoecological implications
Stephen L. Cumbaa, Kenshu Shimada, Todd D. Cook
Palaeogeography, Palaeoclimatology, Palaeoecology 295:199-214

Stephen Cumbaa's page
Kenshu Shimada's page
Todd Cook's page

This is a much-needed review of the copious marine vertebrate fauna of the Western Interior Seaway by some of the best people on this topic I know. Though this is obviously of interest here because of the numbers of marine reptiles many of us think of living in the Western Interior Seaway, this sea was obviously more densely populated with bony and cartilaginous fishes. These authors know these fishes well, and being a little familiar with these collections and taxa, I can see that this was a terribly massive amount of work to compile all of these faunal distributions, primarily because of the care it would take to go through all the hundreds and thousands of tiny fish teeth from these sites. Even though they only report on diversity of each site, not abundance, it is because of the clear limitation that these sites are biased by some degree of time-averaging. Without knowing how long each deposit/accumulation took to get there, abundance is a difficult thing to assess. In the end, this thorough study of the faunas of the WIS is incredibly useful and should play a part in estimates of biodiversity of marine reptiles as well, which presumably preyed on these taxa.

Single source sound production and dynamic beam formation in echolocating harbour porpoises (Phocoena phocoena)
P. T. Madsen, D. Wisniewska, K. Beedholm
The Journal of Experimental Biology 213:3105-3110

Author's page with pdf

I believe that this might be one of the less-conspicuous papers to those that study fossil cetaceans, as it could easily be misconstrued as simply another paper studying the acoustics of echolocation. But these researchers did something very clever – they attached suction-cupped microphones to both pairs of phonic lips of a porpoise to basically see whether both pairs were functioning to produce whistles. They weren’t, as one could glean from the title, and this has major implications for the functional role of the second pair of phonic lips, as well as questions about the evolutionary loss of them in sperm whales. Sperm whales usually fall out as primitive whales in most phylogenetic studies, and because of that one might consider it because they lack the second phonic lips that this is a primitive trait. But some (Cranford et al, 1996) have suggested it was secondarily lost, and this may be the case. If you are working on fossil cetaceans, this study itself may not be directly useful to your work with fossils, but it is important to your understanding of the adaptive and non-adaptive roles of anatomical structures, and how that might influence your perception of how structures associated with echolocation may be retained. I hope those looking into the evolution of echolocation will seriously consider this work.

Hydrodynamics of a ship/whale collision
Gregory K. Silber, Jonathan Slutsky, Shannon Bettridge
Journal of Experimental Marine Biology and Ecology 391:10-19

Author's page with pdf

This study utilized models in a flow tank to simulate the effects of the bow wave of a vessel and how that might interact with a whale. The model of the whale was outfitted with an accelerometer, and though not dynamic itself (no autonomous movement, and obviously no behavior), the accelerometer helped convey the data about how the whale model responded to wave propagation around the vessel as it passed. I’m personally more keen on seeing further data on whale strikes in real situations, but this study goes as far as one could without using living animals to get at some fundamental questions about flow around boats and whether whales are in any special danger of impact due to hydrodynamics. Though the authors stress how this might affect policies about vessel speed in whale-inhabited waterways (which is important), I would argue that one also must use this to consider how to modify vessel design to minimize the hydrodynamics that enhance the danger of collisions with whales. The former is obviously cheaper and easier to implement, but the latter is certainly worth considering.

Change in the foraging strategy of female South American sea lions (Carnivora: Pinnipedia) after partutition
Massimilliano Drago, Luis Cardona, Enrique A. Crespo, Nestor Garcia, Santiago Ameghino, Alex Aguilar
Scientia Marina 74(3):589-598
(free pdf at journal site)

The study of stable isotopes as a proxy for diet is widely recognized as a good technique for sorting out not only the diets of modern marine mammals, but those of fossil taxa as well. Curiously enough, much of the data on the isotopic composition of primary producers and potential prey species that are the sources of these isotopes in marine mammals is lacking for many environments, as is data on how the diets of these animals can change in small ways for short periods of time that may or may not be reflected in tooth enamel. If the changes are temporary, serial sampling may pickup some oddity, but without the sort of data that would answer the question. Plus, tooth enamel records only the isotopic record of the individual while the tooth is being formed, and the data presented here about the isotopic signature of coastal-benthic predation by post-partum female Otaria is likely never to be recorded in their teeth because their teeth have already developed. If one were to study the dental microwear of these same individuals and compare it with the data from their tooth-enamel based isotopes, one would find conflicting signals. It isn’t that either method is wrong, but that they sample the diet of the animal in different temporal and life history scales, which should be seen as an opportunity, not a limitation. In this case, these authors focus their work on the immediately relevant results of how these sea lions’ diets change after giving birth, but I would argue that for the paleobiologist, this is a clear reminder of the need for consideration of the minor changes in behavior that come with life history events that can have a big impact on the dental microwear or isotope record of individual specimens being studied. Hence, the most obvious solution to that is to consider these limitations when dealing with small samples (which some fossil taxa force us to work with), and when possible, use large samples.

Age and growth of franciscana dolphins, Pontoporia blainvillei (Cetacea: Pontoporiidae) incidentally caught off southern Brazile and northern Argentina
Silvina Botta, Eduardo R. Secchi, Monica M. C. Muelbert, Daniel Danilewicz, Maria Fernanda Negri, Humberto Luis Cappozzo, Aleta A. Hohn
Journal of the Marine Biological Association of the United Kingdom

With a large sample size (N=291) incidentally caught in fishing nets over an 11 year period, the authors were able to report the rate of growth for this species in a detailed fashion, with care taken for how gender may have a role. Though they found no significant differences between genders, their data seem to show that females start out consistently a little larger than males, even though their rates of growth do not seem to differ, except perhaps in the first two years of life (after which female growth rates are slightly greater than males). Although this is of minimal interest to a paleobiologist, it is important data to keep straight when further discussions about sexual dimorphism are brought up for fossil cetaceans.

Does dispersal across an aquatic geographic barrier obscure phylogeographic structure in the diamond-backed watersnake (Nerodia rhombifer)?
Matthew C. Brandley, Tim J. Guiher, R. Alexander Pyron, Christopher T. Winne, Frank T. Burbrink
Molecular Phylogenetics and Evolution 57(552-560)

Frank Burbrink's page

Ok, this may be mistaken for something marginally related to aquatic amniotes, but this is getting at something worth understanding with regard to the origins of aquatic amniotes – how can freshwater systems be a barrier or a habitat, and when does it matter? Joshua Samuels (John Day) and I have been talking about this together for years, and hopefully we’ll come to writing something about it someday, but in the meantime, let’s focus on the paper. The authors here simply compared the relatedness of populations of watersnakes around the Mississippi River, finding that the best explanation for the divide in the genotypes of populations was the Mississippi River as a barrier. Not only that, but that the divergence date of this barrier is likely to have been during the Pleistocene, during an interglacial when the river may have been much wider. This is particularly compelling, considering that this is a watersnake, not a dry-desert-loving rattlesnake. This taxon can cross the Mississippi River, yet reproduction must be a behaviorally complex enough event that the river has succeeded in being a barrier to these populations sharing with each other reproductively. What does this mean to the paleobiologist? Perhaps the notion of a river as a barrier, at least in some fashion (perhaps not distribution, but widespread dispersal) is possible not only for fully terrestrial taxa, but semiaquatic ones as well.

There are plenty more reviews coming, and I hope to have some new material on Eocene Sirenia and trichechid tooth development to share soon as well.
Cheers!

Brian

Recent Events: Physical Drivers and Marine Tetrapod Evolution – Symposium at the Society of Vertebrate Paleontology

2010-10-27T07:50:00.009-04:00

It has been WAY too long since my last post, my sincerest apologies. I was consumed with a handful of projects, some of which are submitted, and some of which I presented at the Society of Vertebrate Paleontology meeting in Pittsbugh, PA this past October 10-13.

I fully intend to blog on some of this new material soon, but want to start with a couple of things. 1) A report on a symposium held at the recent Society of Vertebrate Paleontology meeting, and 2) a new series of blog posts reviewing recent literature and its relevance to the study of aquatic amniote evolution studies. I’ll get to the latter in my next post, but let me get started with this report on the recent (October 11, 2010) SVP Symposium titled, “Physical Drivers in Marine Tetrapod Evolution”. I’m keeping this brief, not only to save you from my usual boring wordiness, but also to protect the rights of authors of these presentations from having their unpublished material shared without their permission.

The symposium was organized by Neil Kelley (UC Davis) and R. Ewan Fordyce (University of Otago). Neil is a promising graduate student studying Triassic marine reptiles, and Ewan is one of the world’s leading experts on fossil cetaceans, and together it was a good match that brought lots of good minds together.

Neil Kelley and R. Ewan Fordyce, the organizers of the symposium, "Physical Drivers and Marine Tetrapod Evolution"

Among the minds brought together were (presented listed here only, though obviously many had co-authors that significantly contributed):

Neil Kelley (UC Davis, USA)

R. Ewan Fordyce (University of Otago, New Zealand)

Olivier Rieppel (Field Museum, USA)

Valentin Fischer (Royal Belgian Institute for Natural Science, Belgium)

Michael Polcyn (Southern Methodist University, USA)

Louis Jacobs (Southern Methodist University, USA)

James Parham (Alabama Museum of Natural History, USA)

Sanja Hinic-Frlog (Carleton University, Canada)

Tatsuro Ando (Ashoro Museum, Japan)

Brian Beatty (New York College of Osteopathic Medicine, USA)

Naoki Kohno (National Museum of Nature and Science, Japan)

Edward Davis (University of Oregon, USA)

Carolina Gutstein (Universidad de Chile, Chile)

Erich Fitzgerald (Museum Victoria, Australia)

Felix Marx (University of Otago, New Zealand)

Nicholas Pyenson (Smithsonian Institution, USA)

Topics covered included a variety of methods, details, and scales, though some common themes were:

How aquatic tetrapod groups have and have not been affected by the changing coastlines, chemistry, and productivity of the world’s oceans. I found it dumbfounding that so many variables affect diversity and distributions of these groups, and controlling for them is the challenge we all faced. Some did so by looking at distribution correlations, others by ecological variables such as isotope geochemistry or dental microwear. Methods here included:

Morphometrics of locomotor adaptations
Dental microwear
Stable isotope geochemistry
Distribution patterns
Bottom-up or top-down ecosystem design
Sea level changes and its effect on available habitat, and the use of freshwater by some usually marine groups.
Associations of taxa as implications of their ecology
Spatial and temporal changes in diversity correlating with global climate events

Some authors reviewed some unrecognized diversity, not only taxonomically but also in terms of ecological roles, that revise our understanding of how earth history may or may not have affected these groups. One compelling message of this was a clear reminder that we all need to come back to finding more fossils and describing them before jumping into complex analyses of existing records from databases alone.

In a surprising, but great twist, some made a point of looking at the way that some of the diversity and distribution of groups were or weren’t affected by how the animals themselves dealt with the physical environment in terms of sensory perceptions. Thus, not only did we see distribution and ecological variables discussed, but aspects of sensory modalities in some groups and how that could tell us more about where and how they lived and dealt with the changing environment.

Me (Beatty) finishing my talk on dental microwear in the Sirenia (photo by Michael Ayoub)

In the end, the topics covered all had one common theme – that the evolution of aquatic amniotes is very closely linked with the evolution of the Earth. Despite what one might see as an interesting lesson in history, I think that many of these talks demonstrated that for many of the taxa still living today, we can only hope that these lessons learned will help us avoid reliving history, especially those parts that ended in extinction. These are the sorts of studies that make paleontology relevant to modern ecologists and conservationists in the face of global warming.

I think that the symposium was a massive success, particularly because it seems to have encompassed a huge diversity of methods, taxa, and times, and brought people together to share ideas and potentially collaborate. I know I’m already going down the road of starting some new projects with people I spoke with just after the symposium. That is, after all, the more proximate goal of these symposia, and I am glad to have been part of it. I would like to thank Neil and Ewan for inviting me, and thank you for sharing my interest in keeping current with what is going on among aquatic amniotes.

Until next time... which will be soon!

Tooth development in Trichechidae Part I

2010-03-21T22:45:00.002-04:00

Alright, so this is not a complete post, but it's a start.
This Monday I will be visiting the Mammalogy Collection at the AMNH for one last data collection trip for the study of tooth development in the sirenian family Trichechidae. The Trichechidae is the family that includes modern manatees, as well as a number of fossil forms.
Aside from a comparatively abundant Pleistocene fossil record of manatees primarily found in Florida (subspecies Trichechus manatus bakerorum Domning 2005), most fossils of manatees are fairly scarce and poorly preserved, including the two Miocene taxa, Potamosiren and Ribodon, both from the Amazon River Basin of South America. Both of these taxa are known from little more than isolated teeth and some fragmentary maxillary or mandibular chunks.
But, thanks to two features of the skulls of fossil forms that pull their relationship closest to the modern manatees, there is a couple of oddball fossil forms from Belgium and Germany that ally closely with the Trichechinae (Potamosiren, Ribodon and Trichechus), the Miosirenae (Miosiren and Anomotherium)
Over the next several posts I will try to demonstrate some of the key features of all of these taxa, and how understanding some of the unique specializations in modern Trichechus (especially how those features in modern Trichechus vary inter- and intraspecifically), we can better grasp how these features evolved, possibly as a response to a rapid increase in abrasives in their mouths thanks to the uplift of the Andes.

Archosauriform dentitions possibly constrained by development differently than mammals

2010-02-25T23:39:00.000-05:00

Hi folks, I'm glad to be back after something of a hiatus. I had some important personal reasons to be away, but now am back in business and have several posts ready to go for the next several weeks, with many more in the works so I can keep this going regularly. This has become a healthy outlet for my need to share ideas and stimulate my own internal discussions that make my work better (I hope), and it would not be worthwhile if it were not for you readers, so thank you for your time and comments. I read them all, and treasure the time you spend even contemplating my crazy ideas.

To start, I feel it is appropriate to do a brief report about a paper of mine that came out this past summer, coauthored with Andrew Heckert (Appalachia State University, NC) in Historical Biology titled, "A large archosauriform tooth with multiple supernumerary carinae from the Upper Triassic of New Mexico (USA), with comments on carina development and anomalies in the Archosauria"
Whew! Long title, I know, but it was intended to be descriptive.

To summarize, Andy had an unusual tooth and knew I have been focusing some of my energies on paleopathology, especially those of teeth, and suggested that we work together on describing this specimen he collected some years ago from the Triassic of New Mexico.

If you are familiar with archosauriform dentitions like this one, it is ziphodont (mediolaterally appressed, with carinae along the mesial and distal edges) and resembles the tooth of a large number of taxa. The age, locality, and size of the tooth suggests it belongs to a semiaquatic, crocodile-like reptile known as a phytosaur, although it could be from a large rauisuchian or other similar animal.
What matters more is that in addition to the normal carinae on the mesial and distal edges, there are two extra carinae, running parallel to the long axis of the tooth, but found on the lingual surface of the tooth (the tongue-side). Split carinae have been noted in theropods for some time, including tyrannosaurids (Currie et al 1992, Erickson 1995), carcharodontosaurids (Candeiro & Tanke, 2008), and even a split carina was noted in a phytosaur previously (Hungerbuhler 2000). This was the first time anyone had recognized something that was not a split carina, but a duplication of one, including one so far lingually displaced.
This is odd, considering that unlike the tooth deformities found in some sharks that can result from traumas when feeding (Becker et al 2000), carinae are structures of the tooth that are formed during development within the jaw as the tooth forms, and are only surface features. There is no plausible way to consider alterations or duplications of carinae in these teeth as anything but developmental anomalies, for this reason.
But dental variation is quite common in many animals, so it should be such a surprise, should it? This is where it gets interesting... Most dental variation studies are focused on mammals, where tooth development is very well understood, and that understanding centers around the fact that much of the variation is a result of small regional differences in the thickness of enamel in different areas of the tooth. The gene expression aspects of this are now well understood for mammals in general (references abound on this: 1, 2, 3, 4), but less is known about archosauriform tooth development.
Considering that the external morphology of interest is ultimately the surface of the enamel, knowledge about which tissue influences tooth morphology most can be derived from looking at the end product of tooth development, the adult tooth itself. It is rather difficult to observe the stages of development of a fossil organism, but if one can derive development from an adult form, then that's a start. So, if one looks at enamel thickness, one might get at how tooth morphology in this and other archosaurimorphs works.
Thankfully, P. Martin Sander (a hero of mine for all the creative ways he has tried to tackle paleobiological conundrums) has done a significant amount of work in describing the enamel microstructure of a large number of fossil non-mammalian amniotes, including rauisuchians, phytosaurs, and many others (Sander, 1999). It turns out that like our specimen, many non-mammalian amniotes maintain a mostly uniformly thin enamel, including the enamel covering the carinae and their denticles (this is not always the case for the denticles, but is fairly common). This would in turn suggest that their crown morphology is the result of the control of the morphology of the underlying dentine, not the enamel.
This has huge potential implications for the limitations that non-mammalian amniotes have in developing complex crown morphologies like those seen in mammals, and may explain why only a few rare crocs here or there (Simosuchus, etc) have anything but cone-like dentitions. Ornithischian dinosaurs are a whole other group that seem to overcome this hurdle, though at present I don't think anyone is considering the question of how their teeth developed, or even how they are structured in much of a histological sense. If anyone is up for tackling this issue, I am certainly game :-]
All in all, this one tooth led to some tantalizing, if speculative, thoughts on how archosauriform teeth develop, and how that is limited. The paper goes much further into the evo-devo of tooth development and what we know of it in amniotes in general, as well as some coverage of the curisou fact that the serration density of the extra carinae are uniform and identical to that of the normal carinae, suggesting that even with the new carinae, serration density seems to be stable and conserved, perhaps supporting its utility as a phylogenetic character and suggesting a developmental independence between the location of carinae and the morphology of the denticles they have.
I hope you find it as stimulating as I did.

If you want more discussion about this, see coverage on the blog, Chinleana.

Next up:
Sirenian tooth development

New, regular posts are coming, I promise!!!

2010-02-13T09:07:00.000-05:00

Adventures in prehistoric animal reconstructions - A preview of a new reconstruction by Carl Buell of a new desmostylian from Vancouver Island!

2009-10-21T23:08:00.000-04:00

Last summer (2008) I went to Victoria, British Columbia, to work on a new specimen (collected on my birthday in the summer of 2007) of a desmostylian that came from a locality similar to the type locality of Cornwallius sookensis. Joan Kerik, the Collection Manager (an extraordinary one at that) at the Royal British Columbia Museum in Victoria had contacted me a couple of year before regarding Cornwallius, which was something I was working on at the time (just now published in JVP). Eventually when this new material came up which we all expected would be Cornwallius, she connected me with Thomas Cockburn, a Research Associate that specializes in the Sooke Formation invertebrate fauna.
Tom took me to the locality, as well as the type locality of Cornwallius sookensis, Muir Creek. We had an extraordinary time, saw deer eating algae on the rocky intertidal and a bear eating something dead in the intertidal as well. At the new locality we came across only a little new specimen, this time a caudal vertebrae of a cetacean (remember this is Late Oligocene, so it could be from any number of weird cetaceans of the time). But no more desmostylian. Still, I happily had spent the prior two days studying this partial skeleton already in the museum, which includes half a skull and its teeth (except the incisors), a partial scapula, most of a humerus, and most of the vertebrae and ribs. The skull was quite interesting, because it looked very much like the skull of Cornwallius, yet the teeth looked like a smaller version of Behemotops. Behemotops is not known from much of its skull other than the posterior portion (B. katsuiei from Japan - Inuzuka 2001), and the new specimen does is throw much of that out, revising the relationships of the two main clades of Desmostylia and suggesting that Behemotops is more like Cornwallius and Desmostylus than previously asserted.
So, Tom and I are currently working on the manuscript and I asked my friend, Carl Buell if he could draw this new animal so we could submit it as a possible cover for JVP. He is still not finished with the final illustration with a background and all, but I thought it would be nice to share the final draft of what we came up with of what the animal should look like (with a neutral background). Carl said I could post this, but if you have any questions about its use, I would contact him. While you are at it, you should check out his Flick'r page. The only thing that trumps the quality of Carl's illustrations is how wonderful and generous a friend he is.
I hope you enjoy this - for more you'll just have to wait for the paper to come out (here's where I shouldn't, but will, suggest that you urge JVP editors to move fast - I'm just kidding!!!).

the problem with microwear #1 (of many to come)....or... "if seacows eat seagrass, why can't we consider them grazers?"

2009-10-14T17:04:00.001-04:00

Although I haven't published as much as I would like on the subject yet, many of you that know me know that I have spent an inordinate amount of my research life focused on the study of microscopic damage to tooth surfaces, known as dental microwear. Most of this has been focused on marine mammals, particularly members of the Sirenia and Desmostylia, although most members of these groups are extinct. I presented one of the more thorough studies of dental microwear in modern and some fossil Sirenia at the Society of Vertebrate Paleontology meeting in Bristol, UK this year.

But, to give some insight into the reality of such work, the sort that makes me pull my graying hair out, I thought I would share here. WARNING, I may rant about the flawed science of many microwear studies, but only to highlight the complexity of the problem, I do NOT intend this as a criticism of my valued colleagues endeavoring to get to the answers of a VERY complicated, messy bit of science. They deserve credit for having the guts to put it out there, knowing that in the end they will inevitably fall short of the full story - that's the way science goes, sorry everybody. I learned this perhaps a bit too late, but just get used to it and publish!

See, I digressed already!

Ok, so the problems with dental microwear are many, many, many.... but among other things, many folks attempt to apply systems of ecology to many groups of animals across large fields of diversity (and hence, morphology, physiology, and evolutionary background). The classic is the idea of the hippo-ecomorph. There are many fossil mammals with large bodies and short limbs, such as Teleoceras, Coryphodon, etc., that commonly get lumped into being hippo-like in their morphology (which is superficially true) AND lifestyle (which is rarely, if EVER supported by data). The anecdotal comparisons with hippos that most paleontologists make usually only serve to demonstrate their ignorance of modern hippo ecology (being noctural grazers with little to no social system, only found in groups because of their reliance on a scarce resource - water). But nonetheless, you will still find references of Teleoceras as a hippo ecomorph in textbooks and such, even though several thorough studies have shown that the only evidence potentially telling about this indicates that they were very much NOT like hippos.

So how does this relate to dental microwear? In the strange world of classic microwear (excluding some more elaborate confocal microscope-using methods), there is:

an SEM method that visualizes very small portions of the tooth at a high magnification
a light microscopy method that visualizes a larger area of the tooth at a lower magnification

The differences in these methods are great, but the basic idea is that teeth incur damage from what they eat (or more likely, the dirt that is on whatever they are eating), and the small bits of damage can be characterized in different ways that roughly correlate to different diets of grass, browse, or a mix of both.

BUT, as anyone that has ever raised an herbivorous mammal, had a garden, or even made a salad understands, not even the simplest diets can be broken down that simply AND not a single animal on this planet (except for maybe the koala) can ever be described as being a strict consumer of a single plant type. Plants come in all shapes and sizes, as well as all sorts of material properties and abrasiveness. The general notion that the silica nodules, known as phytoliths, that are found to surround vascular bundles in grasses are the cause of the scratchy wear in grazers itself is an example of this issue. Not only have phytoliths been demonstrated to not all have the hardness needed to wear enamel (Sanson, 2007), but many plants that do not have phytoliths wear enamel in very similar patterns. The best example I know are seagrasses and the wear found on the teeth of manatees, Trichechus manatus. Manatees eat a lot of seagrass, yet not a single seagrass has phytoliths inside, so what causes the wear? My research on this of late has pointed in the direction of substrate, specifically siliclastic substrate that some seagrasses like to grow in. In the end, the simple answer to the question of what causes wear is that for seacows, it isn't phytoliths. For all animals in general, it might be better put as - consider all the options before you rule any single thing out, and consider the system at hand. In the end, the data for one ecosystem may ultimately NOT be comparable to another for just this reason.

I will try to continue these rants to cover other aspects of microwear, including issues with methodologies, assumptions, dietary interpretations, and the ever-persistent attempts to apply microwear to fossil organisms, including dinosaurs, despite clear differences in mastication, ecology, etc that should act as BIG warning labels to most people that microwear should not, could not, and cannot be applied in the same way for every animal that ever wore a tooth. The simple notion of using data from one study and comparing it with that of another is a complex matter that needs addressing as well, so I will try to bring it up here as well.

So much to do, so little time! Thanks for your patience and time.
Brian

Misadventures in prehistoric animal reconstructions - The many faces of the Desmostylia I:

2009-09-08T06:09:00.000-04:00

This is Desumon, a cartoon desmostylian that was created by a natural history museum in Japan to help introduce the Desmostylia to the public. Desmostylians are very popular in Japan, which is just another sign of their cultural advancement, in my opinion. I mean, there has to be a correlation between the quality of their science and math education and the preponderance of desmostylians in popular culture.

In my anticipation of seeing what marvelous work comes from an illustration by Carl Buell of a new desmostylian I am working on, I thought it would be fun to have a romp through the strange history of the reconstruction of desmostylians. What follows are simply those images I have on my computer at present, although I'll try to make sure and get some of the older images (including ones that compare desmostylians with multituberculates) scanned for future posts. In general, I have several future posts planned to explore the history of the ways people have reconstructed aquatic amniotes. It is not only illustrative of how our perceptions of those animals have changed over time, but also how we approach reconstructions from a scientific standpoint and why so many paleoartists these days are also such excellent anatomists.

Enough blabbing, here are some Desmostylia!

To start, it is a good idea to present a skeleton to get an idea of what we're working with. This is a nice generalized reconstruction of a desmostylian skeleton. Aside from some large feet, funny angles in their ankles, and slightly short limbs, they are a fairly mundane large mammalian herbivore shape -think Anrsinoitherium or Coryphodon (also animals considered semiaquatic - see future posts for critiques of that!)

But, partly because they have these wide, thick sternebrae and short limbs, just how close to the ground they were has been debated.

Most of all, it is because of the finds of the Utanobori Desmostylus skeletons (such as Utanobori I), and the way they were preserved with their limbs sprawled out, some paleontologists have interpreted the Desmostylia as having a "herpetiform" posture, with limbs sprawled laterally like what is seen in most modern squamates. The debate over this matter became even a series of papers, back and forth between Norihisa Inuzuka and L. Beverly Halstead.

So, many of the following reconstructions are not only coming from an attempt to reconstruct an animal that spends much of its time in the water, but also a very specific interpretation of their limb posture. This is not the normal way in which most people would reconstruct mammalian limbs, which is why I think some of them look a little awkward.

Rather than blab on and on, I'll let them speak for themselves. The pics are in order of most aquatic/herpetiform to most terrestrial.... I'll let you decide what you think is most realistic. For fun, I've numbered them so you can refer to them in comments. Please, tell me which ones you think are most realistic, or most of what your opinion of Desmostylia has been thus far.
Have fun!

1
2
3 4 5
6
7
8
9
10

This is just a start, I'll try to have more on this soon!

Injured fossil mysticete and an investigation of osteosclerosis (and benthic feeding?) in fossil mysticetes

2009-08-19T18:12:00.000-04:00

I'm sorry to have been inactive for so much of the last month, but I've been busily trying to get some papers completed before the all-consuming teaching schedule takes over my life (1st year Anatomy course started today). I will try to be more active and regular with the blog, I promise.

So, to kick off a rejuvenated series, I thought I'd post something new of mine. Below is a press release by the Virginia Museum of Natural History concerning a paper just published through their in-house journal by me and Alton "Butch" Dooley (which is open access at the Jeffersoniana page at the VMNH), a good friend and colleague. After my paper with Bruce Rothschild in 2008 on decompression syndrome in cetaceans, I've had lots of people approach me about paleopathology, and though I am cautious about doing more than I am comfortable with, this project was irresistible.

VMNH assistant curator of vertebrate paleontology, Dr. Alton Dooley, burshes off dirt from the jacket protecting the unearthed whale skull in July 2006 (VMNH)

Butch had been collecting from a Calvert Formation locality (middle Miocene) known as Carmel Church, in VA. He has a very active dig going on with loads of great finds and volunteers that make it really a spectacular piece of work. One of the more complete whales he uncovered was that of an animal known as Diorocetus. It is a mid-sized "cetothere"-grade mysticete whale and this was an exceptionally well preserved specimen, with much of the skeleton and skull intact.

A dorsal view of the baleen whale's skull (Credit VMNH)

First, the whale has an unusual partially-healed break in its mandible. That alone is curious and worth a little discussion. And although I still think we need to take any interpretations of its cause and implications for behavior with a good amount of caution, to me the best part of it has been that this fossil stimulated something else - a look at osteosclerosis in mysticetes. This animal, probably Diorocetus, has some seriously osteosclerotic ribs. It is hard to find good diagnostic specimens of mysticetes that have decent skulls with associated ribs (partly because they are a pain to collect), so when we looked at this we couldn't believe it when we saw this classic "cetothere" with ribs that almost have as much cortical bone thickness as a manatee! Ok, that is perhaps a bit exaggerated, but it is significantly thicker than that found in odontocetes.

An artist's rendition of the possible feeding habit of the baleen whale (Credit Michael Morriss-VMNH)

So then we decided to look for osteosclerosis in other mysticetes, especially fossil taxa, and found that in our preliminary sample that some of the oldest mysticetes, including toothed mysticetes like Aetiocetus, they had a very advanced form of osteosclerosis, and that only "modern" mysticetes, particularly rorquals, have more porous bones like those seen in odontocetes. What this implies for the evolution of benthic feeding and filter feeding in general with mysticetes is interesting, and discussed in the paper'sm discussion section.

In the end, I think we stumbled upon an interesting sort of data about osteosclerosis that we would not have thought to seriously investigate if not for this curious injured individual from Carmel Church. As you will see in the press release, the interpretation of this individual is what gets the hype, although I am personally more confident and thrilled by the osteosclerosis bit. Still, it is food for thought and reminds us that even filter feeding with baleen is not a simple, one-style-fits-all sort of feeding, and it may have started out in a much different way than we may have previously thought.

I would urge you to read the paper and judge it for yourself. The disucssion of the cause and behavior associated with this individual specimen is meant to be speculative, although an intriguing idea, but the best part is the osteosclerosis (in my opinion). Well enough of me, read on....!

*****ALSO - for another media release about this, see the article in the Virginia Pilot, including comments by Mark Uhen and Nick Pyenson.

VMNH PRESS RELEASE

CONTACT:
Ryan Barber
(276) 634-4163

Virginia Museum of Natural History releases 20th installment of the Jeffersoniana scientific publication series
Publication features first published evidence of bottom feeding habits in extinct whales.

MARTINSVILLE, Va. (August 19, 2009) - The Virginia Museum of Natural History has released the 20th installment of its Jeffersoniana scientific publication series, which is now available as a free download from the museum's online store. The publication, titled "Injuries in a Mysticete Skeleton from the Miocene of Virginia", focuses on the mostly complete fossil skeleton of a baleen whale discovered during a museum excavation at the Carmel Church Quarry in Caroline County, Virginia in 2006. Unique features from these particular remains had never been documented in any other fossil baleen whale and give evidence to suggest several previously unpublished theories of the feeding habits of this now extinct species.
Co-authors Dr. Brian Beatty, VMNH museum research associate and assistant professor of anatomy at the New York College of Osteopathic Medicine, and Dr. Alton Dooley, Jr., assistant curator of vertebrate paleontology at VMNH, suggest that the baleen whale was likely a benthic, or bottom feeding animal, primarily obtaining its food from scooping mud from the ocean floor and filtering the sediment from the plentiful fauna living in the sea floor. Such behavior is common in today's gray whales and to a lesser extent in humpback whales. The size and placement of a fracture on the left side of its jaw suggests that the injury likely had occurred during feeding. The characteristics of the injury indicate it was likely the result of a severe impact, likely trauma resulting from benthic feeding.
Supporting this theory is the density of the whale's rib bones. Dense ribs like those seen in this baleen whale are associated in bottom feeding in some other marine mammals, such as the manatee. Moreover, the presence of similar dense ribs in early baleen whale relatives suggests that baleen may have originally evolved to allow feeding from seafloor mud and only later was adapted for capturing fish and shrimp.
In addition, the publication documents the presence of lateralization in a fossil whale for the first time. Lateralization, or handedness, is well-known in humans and occurs in many animals, including modern gray and humpback whales. Like humans, whales are usually right-handed, and primarily feed from the right side of their mouths when they canvas the ocean floor. Such a fracture on the left side of the fossil whale's jaw indicates it favored eating from its left side, a much less frequent occurrence.
The museum has recently made select installments of the Jeffersoniana series available for free download from the museum Web site in an effort to make the scientific research of the museum's full-time curators more widely accessible to the public. Currently, the museum offers editions 17 to 20 of Jeffersoniana as free online downloads, with additional installments planned for release soon. Hardcopy versions of all museum publications are available for purchase from the museum's online store.
Visit www.vmnh.net or call 276-634-4141 for more information.

Review of "Sensory Evolution on the Threshold"

2009-07-01T07:02:00.001-04:00

Last year Hans Thewissen and Sirpa Nummela published an edited volume with Springer Verlag entitled, "Sensory Evolution on the Theshold". The text covers how sensory biology in aquatic amniotes (and other secondarily aquatic tetrapods) copes with perceiving the world around them.
It is an excellent, uncommon resource, and I highly recommend it. In fact, I reviewed it for the Journal of Mammalian Evolution, and it was published online in October 2008. But, as we all know, printed journals are limited to page charges. Being the wordy sort I am, my initial draft was MUCH longer. Although not as cleanly written, I strove in that version to go through the text in detail and do what I wish more book reviews did - fill in the gaps. That is not to say that this book has many gaps at all, it is really an impressive collection full of details. But being a human endeavor, error is inevitable, and though I doubt I could do as good a job of the book myself, I'm afforded the luxury of simply reading it and noticing some references that are missing. So, herewith I present the full version of the review as a wrote it initially. Though the starting phrases are similar, the content is vastly different in its scope, mainly because large parts had to be edited out to fit within the limitations of a printed journal. This is NOT the same text as the printed review, but I hope it might be useful, mainly for the additional references, so that students of these subjects might have less searching to do.

(NOTE: I would strongly suggest that if this interests you, that you consider joining the Society for the Study of Mammalian Evolution - the membership is only $35, you get the journal and would be in some rare company because the membership of the group is unusually small, considering how many folks study mammal evolution. So join the group!)

So, here is the unabridged version of the review:

Adaptive Convergences in Perception Recognized

Sensory Evolution on the Threshold – Adaptations in Secondarily Aquatic Vertebrates. Edited by J. G. M. Thewissen and Sirpa Nummela. Berkeley: University of California Press. 2008. 351 pp., $75 (cloth). ISBN 978-0-520-252783.

by Brian Lee Beatty

Functional morphology has its limitations, partly because of the inability to divorce the influences of ancestry from function in understanding the form of a given structure. For instance, hypsodonty in a horses, camels, and oreodonts are commonly given examples of adaptation to grazing, yet once evolved, hypsodonty may have simply added to niche breadth and not restricted an animal’s diet to grass exclusively (Feranec, 2003; Mihlbachler and Solounias, 2006). Though the source of morphology can never reasonably be categorized as “inherited” versus “functional”, as these two are not likely to exist without each other, the study of how distinct clades converge on similar forms and specializations is perhaps the best way in which to understand how organisms adapt to different foods, environments, and lifestyles. Once one gets past their charismatic megafauna role in popular culture, marine mammals can be seen as ideal study animals for looking at such convergences because of the numerous times they have returned to an aquatic lifestyle. The physical and chemical environments of air versus water are very, very different (Denny, 1993), and the body forms of marine mammals have proven to be exemplars of convergence in form for functional reasons (Fish, 2000; Pabst et al., 1999). Though marine mammals are similar in physiology and anatomy to the best known vertebrates, mice and men, they are not a natural group and focusing only on them leaves out the majority of vertebrates and far more than half of the clades that have returned to an aquatic lifestyle. The editors of Sensory Evolution on the Threshold, J. G. M. Thewissen and Sirpa Nummela, are known for their work on marine mammals (Nummela et al., 2004), but it is clear from this book that they recognize the importance of having a broader view of secondarily aquatic vertebrates and how many have converged on similar forms despite very disparate ancestries.

In Sensory Evolution on the Threshold, we get the most complete review I have seen of sensory biology and physics in secondarily aquatic vertebrates, from lissamphibia to squamates, birds, and mammals with no particular bias toward one group. The book starts with a concise, but detailed account of the diversity of secondarily aquatic vertebrates, with sections for each major group of vertebrates written by separate authors, some of which are authors of separate chapters in the book. These short sections detailing groups such as lissamphibia, birds, and mammals are nice brief summaries and do the most comprehensive job of reviewing the diversity of secondarily aquatic vertebrates that I have ever seen. I could envision myself citing them frequently, if it weren’t for the complicated act of citing a section within a chapter within an edited volume, each with separate authors/editors. Though they may be complicated to cite, each of these sections is worth it as a starting point for anyone starting work on these groups.

After this brief introductory chapter, the text is broken down into six sections, one for each sense: chemical senses, vision, hearing, balance, mechanoreception, as well as magnetoreception and electroreception. Each of these sections begins with a chapter on the physics and biology of that sensory modality in water. At first I found myself frustrated by reading so many reviews of topics already familiar from other books on specific sensory systems (Land and Nilsson, 2002; Smith, 2000; Stebbins, 1983), but realized that not only do these chapters help ease readers not familiar with these other works, but it also helps the reader construct ideas about what information is important to understanding the discussions of the anatomy and physiology that follow in chapters detailing how these senses work in various aquatic groups.

Chemical senses comprise seven chapters of their own, giving them more pages than any other sensory modality covered in this book. Though not as important to marine mammals as to other aquatic vertebrates, chemical senses are so complex and important to virtually all other vertebrates that they certainly warrant the attention.

For example, in Chapters 2, 3, 4 and 5 the detailed account of the role of the primary olfactory nerves and the vomeronasal organ in the reception of different stimuli really conveys how vomeronasal function is not cut-and-dry. In Chapters 4 (by Reiss and Eisthen) and 5 (by Schwenk), we get a glimpse of how nasal cavities in lissamphibians and nonavian reptiles can link subtle features of internal morphology to chemoreceptive abilities and the interplay between breathing, eating, and olfaction. Chapters such as this make it easy to imagine this as a starting point for people working on sensory adaptations in tetrapod origins or even Sauropterygia. Schwenk even provides a page or two on mosasaurs, phytosaurs, and plesiosaurs, full of inferences and insights that cannot help but stimulate speculation.

Chapter 6 (by Hieronymous) covers aquatic birds in a brief, detailed anatomical way. Though there is no doubt that many birds are aquatic, the amount of time and manner in which they use water is so diverse that birds (Hémery, 2001; Kristoffersen, 2001), perhaps like large ungulates, make it hard to narrowly define ‘semiaquatic’. This problem itself is probably responsible for many paleoecological misunderstandings about the Neornithes, as well as pterosaurs (Mazin, 2001). Hieronymous is an example of clarity when it comes to restricting how he partitions the continuum from terrestrial to fully aquatic. Hieronymous starts out defining what he means by ‘aquatic’ and keeps the chapter limited to a review of general details of what is known for major groups and points out what research is sorely lacking. These gaps in the knowledge of bird biology must be systemic, as even though Hieronymous provides far more details, this chapter reminds me of reviews on bird feeding biology (Rubega, 2000) that also point out the large gaps in our knowledge of modern taxa. Like many of the chapters in this volume, perhaps excluding those on vision, Hieronymous places this limited data optimized on a cladogram, hinting at what may be assumed and what work there is to be done.

Pihlström’s chapter (7) on chemical sense in aquatic mammals touches on the little published information there is for fossil groups briefly, but focuses on modern mammal groups. Pihlström demonstrates his attention to detail in noting the difference between mysticete and odontocete olfactory anatomy, adding to the growing amount of evidence informing us about the big physiological differences between these two groups as they diverged in the late Eocene and early Oligocene (Beatty and Rothschild, 2008; Fitzgerald, 2006; Lindberg and Pyenson, 2007). The only modern aquatic non-cetacean artiodactyls are the Hippopotamidae, and it is unfortunate that Pihlström’s review of this family does not more thoroughly include some significant findings of the role of olfaction in behavior (Zapico, 1999) that demonstrate how terrestrial these animals really are. Still, Pihlström demonstrates his mastery over this topic in his analysis of olfactory bulb volume with respect to body size of some of the smaller semiaquatic mammals in the conclusion of this chapter. Despite how anecdotal the data may suggest a reduction in olfactory bulb volume with becoming semiaquatic, he deftly conveys a need for caution in light of the fact that many semiaquatic taxa are larger than other non-semiaquatic sister taxa, as his data suggests that the only significant differences in olfactory bulb size seem to occur with fully aquatic taxa. Though this leaves more questions than answers, it gives me hope that chemoreception may be a possible dividing line between aquatic and semiaquatic mammals.

The second sensory modality covered is vision. Starting with Kröger’s chapter (8) on the physics of light in air and water, he brings up quite a number of important and novel concerns about vision underwater as compared to terrestrial environments. And though he succeeds in addressing the importance of pressure, sediment loads and salinity in how it may affect eyes as organs when exposed to different aquatic environments, the differences among aquatic habitats with respect to the role of temperature or salinity on the refractive index was not mentioned, even though this data is available (Denny, 1993). Though this does not devalue this useful chapter significantly, this information could be important to animals that move between environments of different temperature and/or osmolarity (e.g., deep diving cetaceans, manatees, possibly many transitional forms). Perhaps more importantly, though subsequent chapters make use of diopters as important units of vision, this chapter does not describe what they are or how they are measured. Even though not important to explain methodologically here, it would have been a better use of the space given to the speed of light in air and water, which has less relevance to the comparative anatomy.

Kröger and Katzir’s chapter (9) on the anatomy and physiology of eyes in aquatic tetrapods reviews specializations of the eyes of modern aquatic tetrapods for not only being fully aquatic, but also goes into detailed discussions of how a number of groups deal with vision when in water as well as when in air. In addition, their discussion of the meaning of eye size for vision in ichthyosaurs is expertly executed, as are the lengthy discussions of how many birds correct for the refraction of underwater prey when hunting from the air, and how odontocete eyes function. For the sake of completeness I feel it useful to report some recent references to the anatomy of Harderian glands in odontocetes (Bodyak and Stepanova, 1994; Ortiz et al., 2007) that are lacking in their discussion of the so-called ‘whale tear’, though this is hardly an oversight of much importance. Likewise, the hypothesis that Platanista (the South Asian river dolphin) may be able to use its light sensitive eyes to form an image in air (Waller, 1983) is not evaluated, and discussion of the use of these eyes as means to identify the surface during side-swimming (Purves and Pilleri, 1973) is absent, despite its relevance when comparing these with other river dolphins whose environments are similarly murky but lack such visual atrophy. The review of vision in sirenians is very thorough, in particular with its reference to findings about manatee corneal vascularity, which has recently been shown to be the result of a lack of expression of sflt-1, which is the normal means of suppressing vascularity in the cornea of all other mammals (Ambati et al., 2006).

Regarding perhaps the most obvious question that comes to mind when one sees this book, the position of orbits on the skull of aquatic and semiaquatic taxa (such as the hippopotamus staring at you from the cover of the book), the authors here only devote a brief discussion. This discussion is unfortunately very superficial, with apparently little care to discern between the derived states of the position of the orbits in the examples they provide to determine the ancestral state of Cetaceans. I believe the authors would not be so likely to continue to draw comparisons to hippos if they had been more careful to note that orbit position Hippopotamus is much more dorsal and derived than in Choeropsis or the putative ancestors of hippos, anthracotheriids. Similarly, there is very little reason to believe that the ‘transitional form’ Ambulocetus represents the ancestral state of subsequent archaeocetes, as all putative sister taxa to cetaceans have laterally-oriented orbits, including anthracotheriids, cebochoerids (Theodor and Foss, 2005), and raoellids (Thewissen et al., 2007) (though it is clear that the authors could not have included this latter reference in the time frame of publishing this chapter). Still, this chapter should be recognized for being a detailed review of a very complex and important subject in the study of aquatic tetrapods, and these omissions should be seen as stimuli for research, not faults.

Hearing is perhaps the sensory modality that has received the most attention with respect to aquatic mammals, particularly because of specializations for echolocation found in cetaceans. Nummela and Thewissen’s chapter on the physics of sound in air and water is the most clear and concise explanations of this topic I have seen, particularly with respect to the importance of acoustic impedance. This chapter is deficient in data comparing how the speed of sound varies in water of different salinities and temperatures, even though its importance is acknowledged in the text and data of this sort is available (Denny, 1993). The chapters on hearing in aquatic amphibians, reptiles, and birds by Hetherington, and mammals by Nummela are not only thorough in their descriptions of data for modern taxa, but Hetherington’s chapter is particularly attentive to fossil amniote taxa as well. I was a bit disappointed that no discussion of hearing in hippopotamids was included in Nummela’s chapter, especially with regard to new information on underwater hearing in common hippos that has recently come to light (Barklow, 2004).

The sense of balance is started with a chapter (14) by Sipla and Spoor on “The Physics and Physiology of Balance”, which is kept concise and clear. Georgi and Sipla’s following chapter (15) on balance in aquatic reptiles and birds avoids repeating details of how semicircular canals work and gets straight to exploring how canal shape changes may reflect aquatic specializations. In so doing, they help convey the importance of phylogenetic context, as the aquatic specializations of many non-mammalian amniotes can only be recognized in comparison with other close relatives, and not necessarily as “rules of construction” of their own. But some patterns do emerge from their presentation of original data and discriminant function analyses, making this chapter a valuable early look at their research that can be found nowhere else.

Likewise, Spoor & Thewissen’s chapter (16) on the semicircular canals of aquatic and semiaquatic mammals presents not only a complete review of previous research, but adds considerably more new data and analysis as well. Of particular interest are the new, conservative estimates about semicircular duct lumen size and how it may affect a canal’s response speed, as well as new data and analysis of pinnipeds, otters, and other semiaquatic rodents and monotremes. One minor technical error is the omission of one citation from the literature cited that is referenced in the text (Jansen and Jansen, 1969), an error so minor it is only worth noting here for the sake of completeness.

Instead of studies of nociception, thermoreception, muscle spindles, or even general spinal nerve mechanoreceptors, Denhardt & Mauck’s (chapter 17) introduction to the physics and physiology of mechanoreception, as well as their following chapter (18) on mechanoreception in secondarily aquatic vertebrates, focus almost entirely on the trigeminal system of mechanoreception that innervates facial areas. The reason for this becomes clear, as this is where most aquatic specializations exist for actively seeking prey items. The attention to the work of Daphne Soares and the folks at the University of Maryland on dome pressure receptors in Alligator is particularly striking, as is Denhardt’s own work on pinniped vibrissae. This chapter has an enticing number of notes on what we still need to know, as well as small tastes of unpublished research by Denhardt and Mauck that make it a stimulating read.

The chapter (19) on magnetoreception by Hofmann and Wilkens is brief, but highlights the significant data on magnetoreception in sea turtles as well as the scant data for cetaceans. Though it is disappointing to read that so little research as been done outside of birds due to logistical difficulties in the study of magnetoreception, I suspect someone reading this chapter will be stimulated to invent new ways of exploring this topic and astound us in the future.

Chapter 20 on electroreception is equally brief, primarily because it is a sense largely lost in amniotes even though it is known to have evolved early on in vertebrate evolution. The data presented on monotremes, particularly the platypus, is excellent, though the suggestion that some dolphins (Sotalia) have electrosense is reported based primarily on similarities in vascularity of their vestigial hairless follicles (Mauck et al., 2000) and unpublished research by Denhardt (which is also brought up in Denhardt and Mauck’s chapter on mechanoreception). In addition to these unusual compelling cases, Wilkens and Hofmann do something rare, they report on other aquatic mammals that are known NOT to have electrosensory abilities.

The concluding chapter, by Thewissen and Nummela, presents new preliminary findings concerning the evolution of sensory systems in fossil cetaceans. They manage an exemplary job of applying the concepts for modern animals laid out in the previous chapters, particularly with vision. I was disappointed that for all of the data on fossil whales presented that their only analyses were of absolute eye size and eye size scaled to body size (with a following statement that increased eye size = increased vision), even though recent studies indicate that eye size scales with brain size quite well with little or no indication of visual specializations (Burton, 2006). Likewise, the inference of enhanced mechanoreception based on the pits and grooves on the rostrum of pakicetids is poorly supported. The statement that manatee rostra are densely pitted where their fields of vibrissae occur is inaccurate, and in general comparisons of a pakicetid rostrum’s pits to the muscular hydrostat of a manatee are poorly conceived. In contrast, their discussion of the sensory landscape of cetaceans, especially their figure illustrating their ideas, is compelling. Their overall scenario regarding this landscape is plausible, even though in this context they seem to be treating early cetaceans as a lineage instead of a number of groups that may not represent the ancestral condition of later taxa. The dichotomy did not start with the advent of the Neoceti, and I am surprised that no cladogram with sensory system data optimized on it was presented to depict the diversity of archaeocetes and early Neoceti.

In their approach to coordinating comprehensive reviews of sensory systems in all secondarily aquatic vertebrates, what Thewissen and Nummela have coordinated here can only be compared to other great integrative biology or functional morphology volumes such Feeding (Schwenk, 2000), The Skull: Volume 3 (Hanken and Hall, 1993), Mechanics and Physiology of Animal Swimming (Maddock et al., 1994), or Secondary Adaptation of Tetrapods to Life in Water (Mazin and Buffrénil, 2001). Though it seems like a plethora of details largely concerning modern vertebrates, it is apparent from these authors that there is still much to be done for modern and especially fossil vertebrates. In this volume I hope that current and incoming generations of paleontologists and organismal biologists will see golden opportunities and inspirations for future paths of study. Now, with this book in hand, I hope that path will be taken by many more.

Ambati, B. K., M. Nozaki, N. Singh, A. Takeda, P. D. Jani, T. Suthar, R. J. C. Albuquerque, E. Richter, E. Sakurai, M. T. Newcomb, M. E. Kleinman, R. B. Caldwell, Q. Lin, Y. Ogura, A. Orecchia, D. A. Samuelson, D. W. Agnew, J. St. Leger, W. R. Green, P. J. Mahasreshti, D. T. Curiel, D. Kwan, H. Marsh, S. Ikeda, L. J. Leiper, J. M. Collinson, S. Bogdanovich, T. S. Khurana, M. Shibuya, M. E. Baldwin, N. Ferrara, H.-P. Gerber, S. De Falco, J. Witta, J. Z. Baffi, B. J. Raisler, AND J. Ambati. 2006. Corneal avascularity is due to soluble VEGF receptor-1. Nature, 443(7114):993-997.

Barklow, W. E. 2004. Amphibious communication with sound in hippos, Hippopotamus amphibius. Animal Behaviour, 68:1125-1132.

Beatty, B. L., AND B. M. Rothschild. 2008. Decompression Syndrome and the Evolution of Deep Diving Physiology in the Cetacea. Naturwissenschaften, 95.

Bodyak, N. D., AND L. V. Stepanova. 1994. Harderian gland ultrastructure of the black sea bottlenose dolphin (Tursiops truncatus ponticus). Journal of Morphology, 220(2):207-221.

Burton, R. F. 2006. A new look at the scaling of size in mammalian eyes. Journal of Zoology, 269(2):225-232.

Denny, M. 1993. Air and Water: The Biology and Physics of Life's Media. Princeton University Press, Princeton, 341 p.

Feranec, R. S. 2003. Stable isotopes, hypsodonty, and the paleodiet of Hemiauchenia (Mammalia: Camelidae): a morphological specialization creating ecological generalization. Paleobiology, 29(2):230-242.

Fish, F. E. 2000. Biomechanics and Energetics in Aquatic and Semiaquatic Mammals: Platypus to Whales. Physiological and Biochemical Zoology, 73(6):683-698.

Fitzgerald, E. M. G. 2006. A bizarre new toothed mysticete (Cetacea) form Australia and the early evolution of baleen whales. Proceedings of the Royal Society B, 273(1604):2955-2963.

Hanken, J., AND B. K. Hall. 1993. The Skull: Volume 3 Functional and Evolutionary Mechanisms. The University of Chicago Press, Chicago, 460 p.

Hémery, G. 2001. Biodiversity and adaptations of extant marine birds: an overview, p. 119-139. In J.-M. Mazin and V. d. Buffrénil (eds.), Secondary Adaptation of Tetrapods to Life in Water. Verlag Dr. Friedrich Pfeil, Munchen.

Jansen, J., AND J. K. S. Jansen. 1969. The nervous system of Cetacea, p. 175-252. In H. T. Andersen (ed.), The biology of marine mammals. Academic Press, New York.

Kristoffersen, A. V. 2001. Adaptive specialisation to life in water through the evolutionary history of birds, p. 141-150. In J.-M. Mazin and V. d. Buffrénil (eds.), Secondary Adaptation of Tetrapods to Life in Water. Verlag Dr. Friedrich Pfeil, Munchen.

Land, M. F., AND D.-E. Nilsson. 2002. Animal Eyes. Oxford University Press, New York, 221 p.

Lindberg, D. R., AND N. D. Pyenson. 2007. Things that go bump in the night: evolutionary interactions between cephalopods and cetaceans in the tertiary. LETHAIA, 40(4):335-343.

Maddock, L., Q. Bone, AND J. M. V. Rayner. 1994. Mechanics and physiology of animal swimming. Cambridge University Press, Cambridge, 250 p.

Mauck, B., U. Eysel, AND G. Dehnhardt. 2000. Selective heating of vibrissal follicles in seals (Phoca vitulina) and dolphins (Sotalia fluviatilis guianensis). The Journal of Experimental Biology, 203(14):2125-2131.

Mazin, J.-M. 2001. Mesozoic marine reptiles: an overview, p. 95-117. In J.-M. Mazin and V. d. Buffrénil (eds.), Secondary Adaptation of Tetrapods to Life in Water. Verlag Dr. Friedrich Pfeil, Munchen.

Mazin, J.-M., AND V. d. Buffrénil. 2001. Secondary Adaptation of Tetrapods to Life in Water. Verlag Dr. Friedrich Pfeil, Munchen, 367 p.

Mihlbachler, M. C., AND N. Solounias. 2006. Coevolution of Tooth Crown Height and Diet in Oreodonts (Merycoidodontidae, Artiodactyla) Examined with Phylogenetically Independant Contrasts. Journal of Mammalian Evolution, 13:11-36.

Nummela, S., J. G. M. Thewissen, S. Bajpai, S. T. Hussain, AND K. Kumar. 2004. Eocene evolution of whale hearing. Nature, 430(7001):776-778.

Ortiz, G. G., A. Feria-Velasco, R. L. Tarpley, O. K. Bitzer-Quintero, S. A. Rosales-Corral, I. E. Velázquez-Brizuela, O. G. López-Navarro, AND R. J. Reiter. 2007. The Orbital Harderian Gland of the Male Atlantic Bottlenose Dolphin (Tursiops truncatus): A Morphological Study. Anatomia, Histologia, Embryologia, 36(3):209-214.

Pabst, D. A., S. A. Rommel, AND W. A. McLellan. 1999. The Functional Morphology of Marine Mammals, p. 15-72. In J. E. Reynolds III and S. A. Rommel (eds.), Biology of Marine Mammals. Smithsonian Institution Press, Washington, DC.

Purves, P. E., AND G. Pilleri. 1973. Observations on the Ear, Nose, Throat and Eye of Platanista indi, p. 13-57. In G. Pilleri (ed.), Investigations on Cetacea.Volume V. G. Pilleri, Berne (Switzerland).

Rubega, M. 2000. Feeding in Birds: Approaches and Opportunities, p. 395-408. In K. Schwenk (ed.), Feeding: Form, Function, and Evolution in Tetrapod Vertebrates. Academic Press, New York.

Schwenk, K. 2000. Feeding: Form, Function, and Evolution in Tetrapod Vertebrates. Academic Press, New York, 537 p.

Smith, C. U. M. 2000. Biology of Sensory Systems. John Wiley and Sons, New York, 300 p.

Stebbins, W. C. 1983. The Acoustic Sense of Animals. Harvard University Press, Cambridge, MA, 168 p.

Theodor, J. M., AND S. E. Foss. 2005. Deciduous Dentitions of Eocene Cebochoerid Artiodactyls and Cetartiodactyl Relationships. Journal of Mammalian Evolution, 12(1/2):161-181.

Thewissen, J. G. M., L. N. Cooper, M. T. Clementz, S. Bajpai, AND B. N. Tiwari. 2007. Whales originated from aquatic artiodactyls in the Eocene epoch of India. Nature, 450(7173):1190-1194.

Waller, G. N. H. 1983. Is the blind river dolphin sightless? Aquatic Mammals, 10:106-108.

Zapico, T. A. 1999. First documentation of flehmen in a common hippopotamus (Hippopotamus amphibius). Zoo Biology, 18(5):415-420.

Paleobiology, the best excuse to have a broad focus

2009-06-24T21:15:00.001-04:00

Ok, to start I would like to present something that I see as a fundamental aspect of the profession of being a paleontologist - the opportunity to delve into many aspects of science, in a word, being a polymath. I am no polymath, and I don't think that most people that would claim to be should be doing so, but it is unavoidable and irresistible to learn and practice the various disciplines of science when one is a paleontologist.

Although most of us would say that isn't so, perhaps after years of focus describing the same group(s) of fossil animals, there are many fields of science one has to be familiar with to gain any competency in that. Among the skills needed, one must be a an anatomist, geologist, evolutionary biologist, and often practice many other skills such as spelunking, camping (and its various skills of its own), illustration (long gone are the days in which most professionals have illustrators that work for them full time), microscopy, and statistics.

But paleontology isn't restrained to those disciplines either. I recall telling my father many years ago, when he asked, "Are you sure you want to be a paleontologist?", that I commented that in a way, because paleontology is simply the record of the history of life, that it is justifiable to use all means and methods at better understanding that history. If something deemed it necessary for one to understand physiology or chemistry or contact mechanics to figure out how something an ancient organism was like, one could and should. Obviously we cannot all do everything, and for efficiency's sake, we need to collaborate with other specialists when those needs arise. But if there are topics outside the mainstream of classic paleontological methods, such as finding fossils, comparative anatomy, and systematics, the opportunity to subspecialize is there.

Most museum curators do not, and probaly should not, distract themselves from the business of "normal" paleontology, but there are many, many more positions for paleontologists in other fields in academia in which this sort of uniqueness may prove an advantage.

So why would I post this on a blog about Aquatic Amniotes? Well, if there is one "group" of vertebrates that is optimal for exploring paleobiological methods and questions, it is the aquatic amniotes. They are NOT a phylogenetic grouping, but a grouping unified by common physiological, mechanical, and anatomical problems of being in an aqueous environment. Though they appear to often find solutions to these problems that appear convergent, often they are not. In these cases, they provide an excellent opportunity to explore functional morphology, adaptation, and evolutionary developmental biology.

I hope to follow this post up with some fun examples of how a variety of scientific disciplines can be utilized to understand aquatic amniote evolution. I'll try to bring in some work by others on such fields as geochemistry, modeling, materials science, and pathology to illustrate how diverse the fields being used to study aquatic amniotes are. I hope that at least some of the students that may read this will find it encourages them to broaden their horizons, explore other methods and topics, to make them better paleontologists for the future.

Hippos prancing about underwater (Hippo-Ecomorph Rant #1)

2009-06-22T13:41:00.000-04:00

The origin of most marine mammals invokes some imaginary semiaquatic transitional form. In the last decade, many of these transitional forms have actually been found, including the semiaquatic sirenian, Pezosiren portelli, which I had the honor of collecting with my master's advisor, Daryl Domning, in Jamaica at the end of my undergraduate studies and beginning of my MS in Anatomy at Howard University. Likewise, in 2001 two papers were published in the same week that described fossil ankle bones of whales that conclusively linked the origins of the Cetacea to the Artiodactyla. I remember that day, I think it was Sept 21, 2001, a Friday, because I was interviewing at Johns Hopkins that day. Shawn Zack (now at Marshall) picked me up at the train station and asked me if I had seen the paper by Thewissen and colleagues published on Thursday, and then said that there was another paper published that Friday by Gingerich and colleagues. Since then, the molecular phylogenetic assertions that hippos are the most closely related modern mammal to the Cetacea has gained much more backing, evn though these original papers in 2001 never inform us of what fossil group they are more closely aligned to. Some recent finds in Pakistan by Thewissen and colleagues have claimed an ancestor in an unusual group of terrestrial mammals known as raoellids, though further analysis by Geisler & Theodor calls some questions to exactly which fossil groups are related to cetaceans and which are not. Yet despite this rigor of questioning what are the real sister taxa to cetaceans, the message most in the public and media have gotten is that there is some connection to hippos. Unfortunately, the connection to hippos also leads some people to examine hippos as examples of what the origins of whales were like, even though the fossil record of hippos goes only into the Miocene and the understanding of whether these earliest forms were semiaquatic or not is still very rudimentary.

Hippos, in my opinion, should be considered the poster-child for how paleontologists take their overgeneralized views of modern animal biology/ecology and infer it for fossil organisms without much, if any fustification. I wont go into this too much further, as a hippo-ecomorph rant(s) is certainly already partly written and worth spending some time on.

But, in the hopes of starting the hippo discussion, how they might relate to cetacean origins and better understanding their roles as examples of the semiaquatic "transitional" mammal, and to relate to a very recent paper recently brought to my attention, it is worth discussing one key point, underwater locomotion in hippos.

A recent paper by Coughlin and Fish (2009) about underwater locomotion in the modern common hippo is an informative look at what many people often see as a "transitional state" for the terrestrial to aquatic transition. This paper is excellent, and in an elegant way really get to the heart of how hippo underwater locomotion is unique, and perhaps a good, or not so good, example of how transitional forms may have made it into the water. I am not sure the parallels they draw between hippos as raoellids, or Pezosiren portelli for that matter, are sufficiently supported, but they gently bring it up as a future avenue for research and should be commended for calling attention to the subject in a rigorous way.

The funny thing is, I have seen these sorts of results from a study of this sort many years ago in the work of a master's student from the University of Florida, Matthew Mihlbachler. In his work, notably done on a budget with a stopwatch and VHS recorder, Matt was able to come to much of the same conclusions as Coughlin and Fish (2009). Though his thesis entailed multiple aspects of the paleobiology of some fossil rhinos (which includes some interesting work about paleodemography) Mihlbachler has only published a small amount of this data in a paper about a fossil brontothere with curiously similar short limbs he named Aktautitan hippopotamopus (NOTE: hippopotamopus is not a typo, see the paper for the etymology).

The best part about these two studies is that they ultimately come to the same conclusion - when you look at hippo underwater locomotion, they are unique. Though there may be some parallels to be found in the hydrostasis controls found in either group someday (as Mihlbachler hints at with some data in his thesis), at present all we can say is that, if hippos are a good example of a transitional semiaquatic mammal (which I am not sure I would claim they are), then many of the characteristics we see in whales that lead from that negatively buoyant transitional form need to be further explored (although Sandy Madar has done some excellent work along these lines, as has Lisa Cooper).

All in all, hippos are an excellent source of information for trying to understand how large mammals might adapt to a life that involves more regular use of water, and in that way they may be good examples of the "transitional form" - BUT the notion that the ancestor of cetaceans was a hippo in the way they are today, or worse, the way we THINK they are today, is poorly conceived and unrealistic.

fake Open Access publication

2009-06-18T07:09:00.000-04:00

What can I say? This news from The Scientist was both so shocking yet so believable, that I feel a need to report it here, even though it has nothing to do with aquatic amniotes. I won't do this frequently, as I'd rather keep this focused on ideas and research, but this cannot be ignored. As the editor of an open access journal, PalArch's Journal of Vertebrate Palaeontology, an online, open-access peer-reviewed journal based in the Netherlands (that does not charge anything), I am more than a little interested in the world of open access journals.

Recently, a couple of graduate students from Cornell tested the peer review in the journal, The Open Information Science Journal, published by Bentham Publishers. They submitted a completely fake paper to the journal and without ever hearing any reviews, got a message back that their paper had been reviewed and was accepted. Then the journal asked for the processing fee of $800, which is when these students decided to withdraw the manuscript and avoid paying the money (they are graduate students, after all). This has loads of interesting implications, though I would urge caution in equating suspicion with wrongful or unethical acts. The workings of a journal can be complex and without further comment from the journal in question, I would argue that it is best to assume an error occurred until further information comes out.

Though I think this is either an anomaly from the normal workings of this journal, or only a problem within this journal alone, it does stimulate a question that I am sure is one many people's minds when one is faced with the page charges of many journals, including open access ones. Mainly, the notion of paying to publish a paper suspiciously sounds like a business practice that would work in opposition to editorial inclinations to reject papers, or even delay publications. From a purely business standpoint, when worries of reputation are excluded, it makes more sense to do less work for each paper, which could/should result in a reduced rigor of peer review. I doubt that is occurring with many of our esteemed open access journals, primarily because of the ethics on which they were started, but as open access journals become more common and numerous, the "pay-to-play" option should cause us all to be cautious. This problem is not new, and the idea of paying to publish papers in some journals, or even simply the politics of publishing in some high-profile journals, should have always caused us to wonder about how peer review varies from journal to journal, and even editor to editor. Publishing, just like science, is a human endeavor fraught with error and often bias. But that should encourage caution and discussion and NOT cause us to stop progress in a stalemate of suspicion.

For more on this story, see the report by The Scientist.com

Aquatic Mesozoic Mammals

2009-06-12T20:31:00.000-04:00

I have been working on a Mesozoic mammal with some colleagues in Kansas (Michael Engel) and China (Dong Ren) and cannot help but comment on the strangeness that is the world of Mesozoic mammals, in particular those that are deemed "semiaquatic".

The poster-child for aquatic Mesozoic mammal is Castorocauda, the beaver-like docodontan from the Middle Jurassic Daohugou Beds of Liaoning Province in northern China. This is the same locality that has had the earliest gliding mammal, Volaticotherium, as well as some weird feathered dinosaurs like Epidendripteryx, and the mammal I am studying with Engel and Ren (I promise to share more about this critter when the paper is published). Castorocauda is an interesting animal, if anything because it shows few specializations for an aquatic life other than a beaver-like tail, unusual limb proportions, and larger than normal body size for a Jurassic mammal.

Back in 1994, Fred Szalay proposed that stagodontid marsupials, found in the Cretaceous of North America, were aquatic, based on the morphology of the bones in the ankle. In 2005 Nick Longrich presented an abstract at the meeting, Evolution of Aquatic Tetrapods in Akron, OH (hosted by Hans Thewissen at NEOUCOM), detailing how stagodontids might have been durophagous and semiaquatic, based on aspects of their dentition and postcrania, especially a caudal vertebra that resembled those dirsoventrally compressed caudal vertebrae of beavers which are also found in Castorocauda. Recent studies of stagodontids (Fox & Naylor 2006), however, have discredited these claims of being stagodontids as aquatic, although it would be interesting to see if some of Longrich's ideas can be further explored.

So, if semiaquatic mammals are rare in the Mesozoic, why? It has been fairly well documented that being semiaquatic (whatever that means - I'll rant on this some more in the future to be sure) is energetically more costly than being either fully terrestrial or fully aquatic (Williams 1999), so that may have been a hurdle impassible for them, but then why would so many other mammal groups manage it in the Cenozoic even strictly in freshwater, from a variety of body sizes such as desmans to beavers? Mesozoic mammals had been pegged as limited to smaller body sizes in the past, but it is increasingly evident that this was not the case.

I would suspect it is something altogether much less exciting, and much more mundane, expected, and depressing - the fossil record. The "pull of the recent" strikes again, and this time I wouldn't be surprised that because the fossil record of Mesozoic mammals is limited by exposures and the longer periods of time in which fossils may have been destroyed, we simply have fewer of them.

Plus, it is really hard to recognize some of the subtler aspects of adaptations for being semiaquatic in gorups which are still fairly rarely known from anything more than fragmentary teeth and jaws. Hell, if you had a river otter jaw in your hand, would you know it was semiaquatic? No, at least not until we start getting to understand the finer relationships of the skeletal and dental adaptations of aquatic and semiaquatic mammal mammals in a broader context.

Hmmm.... that is a tempting distraction from Mesozoic mammals, isn't it?

update on Cetacean response to climate change

2009-06-09T07:46:00.000-04:00

I was just reading over another recent paper that may also prove relevant to this post as well as the previous one, so I thought I would post an update.
Site fidelity in cetaceans is not new, but a recent paper by Valenzuela et al (2009) does an excellent job showing that for at least some large mysticetes, site fidelity is a matter of cultural inheritance, and can cause a lack of flexibility (at least in the geologically speaking 'short term') of feeding grounds for some taxa even in bad years.
Obviously, this report does not bode well for balaenids in the oncoming global warming situation, though it may be another facet worth exploring when considering prehistoric cetacean distributions. It may ultimately be outside the realm of possibility to answer such questions, particularly when we still don't have good estimates of simple things like body size of fossil groups (though I know one person is working on that) or how far different taxa may have regularly migrated (which may or may not be consistently related to body size).

Cetacean response to climate change

2009-06-08T13:41:00.000-04:00

A very recent review paper by Colin McLeod (see here for Univ Aberdeen press release) in Endangered Species Research, titled, "Global climate change, range changes and potential implications for the conservation of marine cetaceans: a review and synthesis", raises some critically important points about the distribution of whales and how that is likely to be affected by expected changes in global climate. Obviously, this is very, very important for all of us that care about modern Cetacea as well as the health of the world's oceans in general.

But I would also urge marine mammal paleontologists to consider something else about this paper. Note that McLeod goes through and meticulously reviews the preferred habitats of most modern cetaceans. One should not be surprised to find that very few of these have a fossil record that goes back to the middle Miocene, when the world was much warmer, and the typical polarized distribution of modern cetaceans is, in reality, an effect of the repeated expansions and contractions of many cetaceans that have evolved in favor of colder waters (and its associated productivity) several times within the last 2-3 million years. This antitropical distribution splits sister species from each other by a warm patch of water in tropcical (and sometimes even subtropical) zones.

The conundrum in making the fossil record of whales informative of the problems we are facing today is that the fossil record of cetaceans is best for the Miocene, from a time when they were experiencing a cooling trend, not a warming. The fossil record of cetaceans during the Pliocene and Pleistocene may be better suited for such a comparison to the modern situation, but it is simply not as well studied (or perhaps as abundant) as the Miocene fossil record is. In that way, if one were to try to predict how marine mammals would respond to a warming trend, it would probably be ideal to very carefully explore how they handled this during glacial-interglacial cycles.

BUT, one edge that the Miocene (and likewise late Eocene) has over these glacial times is some insight in the way that cetaceans interact in marine ecosystems that are warm, like those that will eventually come with the changes being wrought on our world. If one wants to best understand how cetaceans may interact when warmer waters dominate the ocean landscape, the Miocene is perhaps a better model system than even the present day. Granted, modern animals are still FAR more important to understanding their future than any fossil taxon (with its own phylogenetic baggage to deal with that could influence the data), the total community structure, distribution patters, and even physical interactions may be in part better understood when looking at an almost worldwide warm world full of cetaceans in the Miocene. For instance, there are clear differences in the distributions of platanistids and eurhinodelphids in the West Atlantic during the Miocene, and better understanding why such similar animals would have latitudinally partitioned a very warm coast is almost impossible to understand from today's taxa, even though it may happen to many of today's species in the not too distant future.

If there are any graduate students looking for projects out there, one I can easily see would be ones utilizing some of Colin McLeod's other work on correlations of prey size and osteological correlates to answering these sorts of questions. Likewise, other groups that have a different response to climate change, seacows, may be a worthwhile avenue to explore some of these questions as well. I wish I could do it all, and though I am trying to get a start with the Sirenia part of the equation, in the end there are too many questions for one person to ask in a lifetime, and I hope someone out there will give some of these studies with cetaceans a try.

Preservation biases of fossil cetaceans

2009-06-04T07:35:00.001-04:00

I have been quietly writing a series of posts for this blog, lengthy and full of figures, and now that I am close to posting some of them, I came across something short and sweet that I cannot resist posting about. So, I guess the longer posts will have to wait.

This morning, when I read the newest MarMamm listserv posts, I came across a new paper on minke whale habitat preferences off the coast of Scotland. Several years ago I would never have read that paper, mainly out of a lack of interest in focusing on baleen whales. Since then I have had the pleasure of working more closely with Alton "Butch" Dooley of the VMNH (see his blog). Butch has been finding numerous, well-preserved, mysticete skulls and skeletons in the Miocene age rocks of Carmel Church Quarry in Virginia. These animals are quite a puzzle at times, mainly because of their size they are rarely so well preserved, and the logistics of collecting them has deterred many in the past and resulted in specimens that a few and far between. Anyone working on dinosaurs may know how it feels, but suffice it to say that if you are interested in really understanding fossil species, preservation and sample sizes matter. As a paleobiologist, what Butch is collecting in VA is an ideal and rare opportunity.

Ok, back to the paper of the morning. Kevin Robinson and colleagues in Scotland and Wales very recently published a paper on the habitat preferences of modern minke whales in the journal, Journal of Coastal Conservation. In it, they present a consistent link between the distribution of minke whales (Balaenoptera acutorostrata) and habitat details, such as seafloor physiography and sediment type.

I know this is a stretch, but I cannot help but think that this close connection of some, but perhaps not all, mysticetes to a habitat type might be useful in explaining the distribution and preservation of large fossil cetaceans. I don't mean to push it too far, but this could serve a role similar to the way terrestrial paleo folks regard the lack of montane taxa preserved (or at least, they all should). I know it is logical, but it is nice to find modern support for the idea that the record of fossil mysticetes may be biased to those that prefer habitats that preserve well.

This may also be a point of curiosity regarding how/why we get physeterid fossils, even though physeterids are supposedly more pelagic. I don't mean that fossil physeterids were not pelagic, but it is worth considering all the possible influences on distribution of fossil cetaceans, and maybe use taphonomy to better understand what animals are part of a local fauna, and which are bodies washing into it from afar.

These are all things to think about, although perhaps nearly impossible to approach as a study due to the complications involved in confirming this sort of data widely for modern mysticetes, and even more difficult for attempting to link studies of physiography and sediment types with meticulously collected fossil mysticetes. But, I hope it is an entertaining thought for the day and look forward to any comments you all might have.
Cheers,
Brian

Yes, another blog....

2009-03-07T18:21:00.000-05:00

Ok, I know the world does not need another blog, but I find myself interested in keeping one so that I can share news and ideas more broadly than just with the Aquatic Amniote Paleobiology group I created on facebook.
You are welcome to join that if you wish, but not everyone wants to join facebook, and this way I hope to reach a broader audience. If would really like this to become a place to exchange ideas and discuss matters of aquatic amniote evolution, and evolutionary biology and paleobiology, especially methods and philosophy, openly.
The first real post will be up soon.
Thanks!
Brian