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

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you from my usual boring wordiness, but also to protect the rights of authors of these presentations from having their unpublished material shared without their permission.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!

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

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:

1. an SEM method that visualizes very small portions of the tooth at a high magnification
2. 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