Wednesday, October 21, 2009
Adventures in prehistoric animal reconstructions - A preview of a new reconstruction by Carl Buell of a new desmostylian from Vancouver Island!
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!!!).
Wednesday, October 14, 2009
the problem with microwear #1 (of many to come)....or... "if seacows eat seagrass, why can't we consider them grazers?"
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
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.
Tuesday, September 8, 2009
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.
This is just a start, I'll try to have more on this soon!
Wednesday, August 19, 2009
Injured fossil mysticete and an investigation of osteosclerosis (and benthic feeding?) in fossil mysticetes
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
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.
Wednesday, July 1, 2009
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.
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
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.
Denny, M. 1993. Air and Water: The Biology and Physics of Life's Media.
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
Hanken, J., AND B. K. Hall. 1993. The Skull: Volume 3 Functional and Evolutionary Mechanisms. The
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,
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.
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.
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,
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 (
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,
Schwenk, K. 2000. Feeding: Form, Function, and Evolution in Tetrapod Vertebrates. Academic Press,
Smith, C. U. M. 2000. Biology of Sensory Systems. John Wiley and Sons,
Stebbins, W. C. 1983. The Acoustic Sense of Animals.
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
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.
Wednesday, June 24, 2009
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.
Monday, June 22, 2009
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.
Thursday, June 18, 2009
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
Friday, June 12, 2009
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?
Tuesday, June 9, 2009
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).
Monday, June 8, 2009
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.