"Knowledge is good." -Faber College Motto

13 March 2015

Delayed Discourse on Diplodocine Discontinuation

Dippy the Diplodocus
The Natural History Museum
It's been another cold, dark winter both literally and, as far as this blog is concerned, figuratively.  I've just returned to Iowa following Cornell's Spring Break and as the snow is melting, the flowers are sprouting, and the weather is warming, I thought it was high time to wake the Mammoth Prairie from its hibernation.
While the winter has been a quiet one in regards to my writing (or at least my writing here; there's been plenty of application and manuscript prep), as per usual paleontology has been making headlines.  There's not much in addressing most of these after the fact, but there was one story that hit a nerve both personally and professionally that I felt was worth revisiting.  I'm betting that the majority of what's left of my audience knows that back in January London's Natural History Museum announced that Dippy, the Diplodocus skeleton that's been the centerpiece of their main hall for nearly four decades is going to be replaced by a blue whale skeleton as part of the museum's renovation project.  I've written before about the personal significance of Dippy to my own development as a paleontologist (the brief synopsis is that he was the key figure in my origin story) and so, like a whole generation of paleontologists, my first reaction was one of dismay.  However, approaching things from a museological standpoint, it's not too hard to come up with a whole list of reasons why a blue whale makes for a better centerpiece.  It's bigger, first of all; bigger, in fact, than any dinosaur or any other vertebrate that has ever lived (unless you buy the upper limits of the mass estimates for some sauropod species, of which it is wise to be extremely skeptical given the scrappiness of the material and the corresponding degree of extrapolation necessary in most cases).  This may sound trivial, but the NHM's central hall was clearly envisioned by its founder Richard Owen and architect Alfred Waterhouse to evoke the style of Europe's great cathedrals, and it has stood the test of time as one of the most spectacular examples of monumental museum architecture in the world.  Diplodocus was undeniably a big animal, but was quite svelte for its size, meaning that Dippy has always been dwarfed by his surroundings; architectural sketches seem to suggest that the whale will fill the space better.  Also, Dippy hails from Wyoming, while the blue whale was found beached in Ireland, meaning that while the star of the museum's show still won't be English, it will at least be from the British Isles.  Dippy, for all his fame, is a cast of a specimen housed in Pittsburgh, while the whale will be the genuine article.  Even the argument that Dippy should be retained because he is the museum's traditional centerpiece don't hold water, as a whale skeleton occupied the space well before the dinosaur made its debut.  And so, despite my personal attachment to Dippy, from pretty much practical and educational standpoint, the whale makes much more sense.
Illustration of the NHM Blue Whale
The Natural History Museum
Professionally, though, there is one aspect of the NHM's plans that troubles me more than it probably should.  The museum has stated that part of its motivation for bringing in the blue whale is to emphasize their focus on the ecology and conservation of modern ecosystems.  Without a doubt, studying and mitigating the impacts of human activity on the natural world is the most important goal of natural science, and in that sense the museum's motivation is laudable.  However, it doesn't necessarily follow that an emphasis on ecology and conservation should displace displays of fossils.  Paleontology suffers from a widespread and misguided perception of obsolescence.  The word dinosaur has, after all (and, again, misguidedly), come to mean something outmoded and inferior and even recently extinct organisms have come to be synonymous with being outdated (see 'gone the way of the dodo').  I don't for a moment suppose that the exhibit designers involved have an anti-paleontology agenda, nor does the displacement of one dinosaur by one whale mean that one of the world's largest fossil repositories will be subbing in pandas, insects, and sea turtles for their ground sloths, ammonites, and plesiosaurs.  However, one cannot help but worry that this will only help reinforce the artificial line between "practical" neobiology and "impractical" paleobiology when in fact, paleontology is (or at least should be) an integral part of ecology, evolutionary biology, and even conservation biology.  I could selfishly point to a paper on which I was a co-author that came out during my blogging hiatus that shows how important paleoecology can be in formulating and testing models of the effects of future environmental change, but for the sake of argument lets stick to whales.  Cetacean paleobiology is a flourishing branch of paleontology, and with good reason.  Between heavy bones, wide distributions, and living in a top-notch preservational environment, whales have a magnificent fossil record that, more clearly than in any other organism, tracks the evolution of land-living animals into marine taxa.  This is most famously illustrated by Phil Gingerich's work on Eocene cetaceans from Pakistan and Egypt, where a spectrum of fossils lying between fully terrestrial cetaceans to seagoing whales with vestigial hind legs have been found.  Elsewhere in the world (my Northwest pride compels me to note that this encompasses the Washington and Oregon coasts) other major transitions, such as the evolution of baleen or the bizarre morphology of river dolphins, are clearly documented by cetacean fossils.  Just as fossils demonstrate how whales have evolved, so too do they reveal how whales have shaped and been shaped by the organisms and environments with which they interact.  Whale paleocology is perhaps best illustrated by the study of whale fall communities, long one of the most important deep-sea ecosystems.  This field of study has yielded myriad papers by researchers from across the globe, one of which (Pyenson & Haasl 2007) is one of the neatest examples out there of how ecology profits when both paleoecological and neoecological data are considered.  So how is this exceptional fossil record relevant to whales now and in the future?  First of all, it shows us how the diversity and ecology of modern whales came to be, putting modern forms in their proper evolutionary context.  Beyond this, understanding when and in which groups major evolutionary or ecological changes occurred allows us to approach the question of which forces have driven whale diversification and extinction and how these changes have affected other organisms, a field of study that has been most prominently (but by no means exclusively) explored by Ewan Fordyce.  Understanding the forces that have shaped whale evolution, particularly during periods of time that differ climatically from today, could in turn play a huge role in predicting the effects that warming oceans, fluctuating food supplies, and interactions with human activity may have on whales and on the organisms and environments with which they interact.  A blue whale, then, is a fantastic choice for conveying the magnificence and precariousness of life on Earth today, but is also just one player in a vast evolutionary saga that can only be fully told by including fossil data.  Put in the proper context, the NHM blue whale could become the world's most prominent illustration of how the big questions about life on Earth both today and in the future are best answered by integrative science that incorporates data from neontologists, paleontologists, climatologists, geologists, and many, many others.  Displayed out of context, it could further reinforce the harmful impression that science operates within compartmentalized disciplines, some of which are more "valuable" than others.  Here's hoping they do the right thing.

03 July 2014

Fossil (Gondwanan) Vertebrate(s) of the Month: Palorchestes & Diprotodon

'Giant Kangaroos & Wombats' by Charles R. Knight
Field Museum of Natural History
When the great paleoartist Charles R. Knight painted the mural at left in the 1920s, he thought he was depicting two unrelated marsupials from the Pleistocene of Australia.  Certainly the two animals would have been familiar to Knight's audience of natural history dilettantes at Chicago's Field Museum; they were among the first fossils ever to be described from Australia - by no less a luminary than Sir Richard Owen - and had become icons of Victorian paleontology.  This is particularly true of Diprotodon, the animal lumbering into view on the right hand side of the mural, which remains one of the most familiar members of the Australian megafauna.  Diprotodon is often referred to as a giant wombat, which is not too far from the truth, as its closest (though still somewhat distant) living relatives are koalas and wombats, and it certainly was a behemoth.  In fact, at around the same size as a large rhinoceros, it was the largest marsupial ever to have lived.  When Owen described Palorchestes 1873, it seemed like a similarly superlative animal: a giant kangaroo, hence its genus name, meaning 'Ancient Leaper' and its appearance in Knight's mural.  Owen was the greatest comparative anatomist of his day and once famously reconstructed the appearance of a moa on the basis of a single bone, but even the best get it wrong sometimes.  It took nearly a century, but in 1958 the Australian paleontologist Jack Woods recognized that the teeth of Palorchestes indicated that it was not, in fact, a kangaroo, but a fairly close relative of Diprotodon.  If an ancient Australia without giant kangaroos seems dull, don't fret: there WERE truly enormous kangaroos in the Pleistocene, and subsequent discoveries have shown that Palorchestes was even weirder than first thought.  The structure of its nasals suggests that the skull supported a tapir-like trunk to go along with its tapir-like teeth, though its elongated, powerful forelimbs, large claws, and grooved lower jaw apparently indicative of a long, flexible tongue impart an appearance that defies comparison to any living mammal (the closest comparisons that spring to mind are extinct ground sloths and chalicotheres).  Incidentally, palorchestid and diprotodontid fossils are often found near billabongs and other bodies of fresh water (possibly due to congregation and mass mortality during droughts), and it's been suggested that their fossils gave rise to the bunyip legend and thus, indirectly, the greatest childrens' book of all time.

15 June 2014

An Exhibit for the Ages: 100 Years of the Laysan Cyclorama

Laysan Cyclorama
Courtesy International Panorama Council
Exactly 100 year sago, on June 15th, 1914, the University of Iowa opened a new exhibit: a cyclorama of the wildlife of Laysan, an atoll at the tail end of the Hawaiian Islands and, at that time, a major seabird rookery.  Many other displays have come and gone at the UI Museum of Natural History, some of which - most notably Rusty the Giant Sloth - have replaced the Laysan albatrosses and frigatebirds as the public "faces" of the museum, but the centenarian exhibit remains the most remarkable of the bunch.  There are probably as many ideas about what makes a great natural history exhibit out there as there are natural historians and museologists, but in my estimation there are five criteria for a really outstanding display, and the Laysan Cyclorama meets each and every one.


  • Historically interesting - The Laysan Cyclorama really got its start in 1902, when UIMNH director Charles Nutting visited the island.  He was enchanted by the nesting birds he saw there and in 1911 he sent taxidermist Homer Dill on an expedition to Laysan (an expedition that was, delightfully, funded in part by proceeds from a skit put on by the football team).  When the specimens collected in 1911 were put on display three years later, the cyclorama became the first exhibit in the museum to depict an entire ecosystem.  This may not sound terribly remarkable, but given that Carl Akeley had only just introduced the concept of creating dioramas that represented ecological snapshots rather than simply displaying individual animals in glass cases, the Laysan Cyclorama was, in fact, part of the leading edge of a major change in the way natural history exhibits were designed.
  • Scientifically important - When the UIMNH expedition visited Laysan in 1911, it was already a dying ecosystem.  The introduction of rabbits to the island in 1903 wreaked havoc on the native plant, insect, and bird life.  Most severely affected were the endemic species that had depended on the vegetation that was decimated by the rabbits.  Three species - the Laysan rail, millerbird, and honeycreeper - went extinct and two - the Laysan finch and duck - survived but remain endangered to the present day.  Specimens of these species on display in the cyclorama and preserved in the collections of the UIMNH and a handful of other museums are the last remaining evidence of the extinct birds and a source of valuable information about the surviving taxa.
  • Educationally effective - The gorgeous, narrow, wood-panelled passageway that leads into the cyclorama leaves little doubt as to the vintage of the exhibit, but the display was ahead of its time in its efforts to teach visitors about the effects of human activity on island ecosystems.  Perhaps the most remarkable thing about about the Laysan Cyclorama is that age has made it an even more valuable educational tool.  Over the course of the intervening century, the last remaining rabbits have been extirpated from Laysan, some native species have begun to recover, and the island has become a natural laboratory for studying the ecology of island ecosystems.  Instead of a window into a lost world, then, the cyclorama represents a look at the beginning of an ecological epic that continues to unfold today.  The modern signage in the exhibit does a nice job showing how this story has developed since 1914 and very effectively demonstrates that ecosystems are not static and that time is an important variable in biology (a lesson near and dear to my heart as a paleontologist).
  • Aesthetically pleasing - A trend in modern biodiversity exhibits is to develop large, walk-through environments rather than classic "window on the world" dioramas (and lest you all think I'm being characteristically curmudgeonly, I think this is generally a trend for the better).  The cyclorama format of the Laysan exhibit anticipates the immersive exhibits of today, but it also retains the artistry and almost obsessive attention to detail that characterize the great dioramas of the early 20th Century.  Dill didn't just bring back bird specimens from his expedition: he brought back sand from Laysan's beaches and rocks, which would literally form the groundwork of the exhibit.  The authenticity of the cyclorama is augmented by the background mural by Charles Corwin, who was not only a talented painter but also a member of the 1911 expedition.  The end product is not only very authentic, but extremely detailed (if you ever have a chance to visit, see if you can pick out the nesting sea turtle) and beautiful to look at.  The intent of the exhibit was to make visitors to feel as though they'd been transported to Laysan, and the fact that it conveys that feeling even today is a testament to how well the designers succeeded.
  • Unique - Other museums have dioramas depicting Pacific island rookeries (the Denver Museum of Nature & Science has a particularly impressive example), but both the cyclorama format and Laysan setting of the UIMNH exhibit make it unique.  Many natural history exhibits are repeated between museums, the best example being the "African watering hole" diorama pioneered by the aforementioned Carl Akeley in Chicago and New York and then repeated ad nauseum by museums across the globe; each iteration is impressive, but the sheer number of them makes each less remarkable than it would otherwise be.  The uniqueness of the Laysan Cyclorama makes it truly stand out.  Not only is the exhibit groundbreaking, important, and educational, but it's something that can only be seen in Iowa, and if you're ever in the area you should do yourself a favor and pay it a visit.
As mentioned above, everyone with an opinion on such things probably has a slightly different idea of what constitutes a great natural history exhibit, and I welcome peoples' comments on favorite displays and criteria for evaluating them.  However, regardless of how you judge exhibits, it's hard to imagine that anyone would find the Laysan Cyclorama to be anything less than remarkable.  So, join me in wishing a Happy 100th Birthday to an exhibit that was ahead of its time, that has told generations of Iowans an important ecological parable, and that looks as good today as it did a century ago!

08 May 2014

Fossil (Gondwanan) Vertebrate of the Month: Thylacosmilus atrox

Thylacosmilus atrox
By Mauricio Antón
Some animals are not as weird as we often think they are (zebras, for example, are really just horses with stripes, a not-uncommon color pattern among mammals).  Some animals are far stranger than people tend to realize (elephant trunks are like no other structure that has ever evolved).  Among my favorite animals, though, are those that people tend to recognize as being strange but that are, in fact, even more bizarre than they might appear at first glance.  The prime example among living animals is the platypus, which is aberrant in almost every single way possible.  This month's featured fossil vertebrate provides a nice paleontological example of an animal who's outer coating of weirdness just hides more profound weirdness underneath.  Thylacosmilus atrox lived in the savannas of South America in the Mio-Pliocene of South America.  A reasonably well-known fossil mammal, it is often referred to as the marsupial sabertooth, a name that highlights the two superficially strange things about it.  Thylacosmilus had among the largest sabers of any predator ever to have lived, and this trait has drawn comparisons to saber-toothed cats and to the cat-like Barbourofelis.  Unlike cats and barbourofelids, though, Thylacosmilus was not a carnivoran.  In fact, it wasn't even a placental mammal, but rather a metatherian more closely related to kangaroos and opossums than to cats.  So, was Thylacosmilus a marsupial that evolved convergently with cats on a continent without carnivorans?  This is certainly how it is often described and depicted (perhaps most notably by the great Czech paleoartist Zdenek Burian), but this view of Thylacosmilus does not do its weirdness justice.  To begin with, it wasn't actually a marsupial, but a member of the Order Sparassodonta a group of stem metatherians endemic to South America.  This means that, while Thylacosmilus was more closely related to marsupials than to placentals, it and its sparassodont kin were only distantly related to both groups.  Secondly, while Thylacosmilus certainly had its share of cat-like features, it was not a perfect felid analog.  As Julie Meachen has shown, there is more than one way to be a sabertooth: some carnivorans have sturdy sabers and gracile arms, while some have long, delicate sabers and robust arms, and some (such as Xenosmilus) don't fall neatly into either category.  With its long, thin sabers, it is tempting to think of Thylacosmilus as the South American version of Smilodon or Barbourofelis, but does the rest of the body follow suit?  As mentioned in a previous post, my student Laurel Perper has been looking into this question by visiting the type specimen of T. atrox at the Field Museum.  Her results show that some aspects of the forelimbs of Thylacosmilus are similar to those of saber-toothed cats, but the robustness of its humerus turned out to be literally off the charts, meaning that Thylacosmilus had arms so beefy that they compare better to those of bears than to even the burliest of cats.  So why is Thylacosmilus so similar to cats in some ways but so different in others?  Is it because it was descended from a very different group of mammals, from which it would have inherited a very different "evolutionary toolkit" than did cats?  Were differences in the environment and climate between North and South America responsible for the weirdness of Thylacosmilus?  Were its robust arms an adaptation to preying upon the unique megafauna of the Pampas, which would have included armored glyptodonts, enormous toxodonts, and sloths and rodents orders of magnitude larger than their living relatives?  Perhaps Thylacosmilus evolved as it did because of competition with other South American predators, most notably the giant "terror birds."  Between the measurements Laurel has made at the Field Museum and those that I intend to make in my upcoming trip to South America, my students and I are hoping to have sufficient data to be able to start answering these questions soon, so if they piqued your curiosity as much as they did mine, stay tuned!

04 May 2014

An Appreciation of Mexican Fossils

It's May 5th, or, if you prefer to use Spanish, el Cinco de Mayo, which means it's time for perhaps the stupidest of all "holidays" (Mexico has a cultural and historical legacy that we in the US can only dream of and yet, generally speaking, the only time we celebrate our neighbor to the south is by getting drunk on cheap margaritas, bad tequila, or Corona on what is not even a major holiday in the country the day allegedly honors).  That said, there are many aspects of Mexico that deserve to be celebrated: the dazzling scientific achievements of the Maya, the monumental architecture and sculpture of the Aztecs, the stunning Baroque design of Spanish colonial buildings, and the powerful modernist art of Diego Rivera, Frida Kahlo, and their contemporaries all spring to mind.  However, Mexico has a heritage that predates its oldest archaeological artifacts.  I can hardly do justice to the entire Mexican fossil record in one off-the-cuff blog post, but here are some highlights of the country's 200+ million year history of vertebrates :

Helicoprion by Ray Troll
The oldest vertebrate fossil in Mexico (or at least the oldest that I could find in the Paleobiology Database) is a specimen of the whorl-toothed "shark" Helicoprion.  Not only is the age of the specimen noteworthy, but the location from which it was recovered, in the central Mexican state of Puebla, is as far south as this most bizarre of chondrichthyans has ever been found, making it geographically superlative as well.

Huehuecuetzpalli mixtecus from Reynoso 1998
Puebla is also home to the most spectacularly-preserved fossils in all of Mexico.  Tlayúa Quarry near Tepexi de Rodríguez represents a Cretaceous reef and preserves a primarily marine fauna, though a few terrestrial vertebrates have been found there as well.  Tlayúa has drawn comparisons to Solnhofen, which is very high praise.  While visiting the collections at the Universidad Nacional Autónoma de México a few years ago, I was fortunate enough to be able to be able to view some of the specimens from this site, and I can vouch for the fact that they are nothing short of spectacular.  The bulk of the vertebrate fossils from the site are fish, but several reptiles have been uncovered as well.  UNAM has a long-standing research program at the site and has established a museum there as well, making this one of the best-studied localities in the country.  The icing on the cake of this spectacular site is that many of the new genera and species from Tlayúa have been named in Nahuatl, giving them marvelous names to match their marvelous preservation; my personal favorite is the early iguana relative Huehuecuetzpalli mixtecus.

Baja California in the Cretaceous, by William Stout
The best place to find dinosaurs in Mexico is the north, particularly in Baja California and Coahuila.  This dinosaur fauna dates to the latest Cretaceous and is dominated by hadrosaurs, some of which grew extremely large.  Incidentally, if this post gets you really excited about Mexican fossils but you lack a passport or the money or time to fly south of the border, you can always check out the Fossil Mysteries exhibit at the San Diego Natural History Museum, the Cretaceous section of which focuses on fossils from the Two Californias (Alta and Baja) and features an excellent mural of Mexican dinosaurs by William Stout.

Mexican fossil horses, UNAM Museo de Geología
Volcaniclastic sediments throughout Mexico preserve a Miocene fauna of which the most impressive and abundant members are horses.  When I travelled to UNAM, it was these fossils that I was visiting, as they were part of my dissertation research on body size evolution in mammals.  Interestingly, and counter to any predictions that one would make based on modern mammals, horses in central Mexico and Oaxaca were much more similar in size to those from Oregon than to those from California or Nevada (an observation for which I have - as yet - no good explanation, though it is intriguing that both landscapes are highly volcanic).  However, my work is just a small, fairly inconsequential drop in the bucket of Miocene mammal studies in Mexico; the one person who has done more to fill the bucket than anyone else is Ismael Ferrusquía-Villafranca, whose lab is responsible for much, if not most, of what we know about the Mexican Neogene (who, besides being a hugely important figure in the field, also happens to be a really nice guy to whom I am still exceedingly grateful for allowing me to work with the collections he has helped amass).

Mexican megafauna mural by Iker Larrauri
Museo Nacional de Antropología
When the Isthmus of Panama closed, Mexico became part of the land bridge connecting North and South America.  Much of the wildlife that migrated north colonized Mexico before the rest of the continent, meaning that South American migrants such as sloths and glyptodonts are well-represented in the Mexican Pleistocene, as are native taxa such as mammoths and saber-toothed cats.  This Panamerican fauna forms the bulk of the displays in the UNAM's fantastic Museo de Geología, as magnificent an example of a classic academic museum as you will find anywhere (also the home of most of the important works of José María Velasco, who really should be one of your favorite old-school paleoartists).  Mexico's Pleistocene fossil record also overlaps with the country's incomparable archaeological record.  To cite just two examples, a mammoth skeleton from Santa Isabel Iztapan shows evidence of butchery by humans, while a camel sacrum from Tequixquiac carved to resemble the head of a wolf or coyote represents one of the earliest works of art in Mesoamerica.

01 May 2014

Conference Review: North Central GSA

Smilodon Mosaic in the Nebraska State Capitol
Ask a random person on the street what state they most closely associate with fossils and, after having stared at you you just long enough to determine just what kind of lunatic you are for asking such a bizarre question, they will probably respond with one of the Northern Rockies states (I'd bet that the most common response would be Montana, though I have no actual data to back this up).  However, a case could be made that they all should be answering Nebraska, which is probably the best place on Earth to find Cenozoic mammal fossils (it's also very good for Cretaceous marine fossils, if that's the sort of thing that floats your boat).  This is best illustrated by proboscideans, which have been found in 91 of the state's 93 counties, but mammals of all kinds have been found throughout the state.  The University of Nebraska has had an active paleontology program since E.H. Barbour's arrival in 1891, and the quality of the collections and research at the university have made Lincoln a paleontological mecca ever since.  Needless to say, then, when the Geological Society of America holds a regional meeting in town, paleontology is going to headline the program.  I attended the North-Central GSA in Lincoln last week, and here are some of my thoughts on the paleontology currently being conducted in the middle part of the continent (the abstracts and presentations can be viewed here if you want more detailed information on any of the talks):

  • Nebraska professor Jason Head spoke about a subject very near and dear to my heart: how the fossil record can inform models of future ecological change.  Ecological niche models take the climatic conditions in which an organism lives today and use these to predict where the range of that animal might shift as climate warms in the future.  However, many studies have shown that these models generally fail (sometimes spectacularly) to predict ranges of species during periods of past climate change.  Jason Head's study was interesting because he used fossil occurrence data and paleoclimatic reconstructions for boid snakes to augment ecological niche models, and found that the models that included paleoecological data predicted somewhat wider ranges for rubber and rosy boas in the future than did models based purely on modern data.
  • Did you know sloths have an especially high rate of dental anomalies (i.e., they frequently have either fewer or extra teeth)?  I didn't until I saw Robert McAfee's talk last week.  What's more, not only do living tree sloths often have abnormal numbers of teeth, but so did extinct ground sloths.  In fact, McAfee suggested that rates of caniniform tooth loss in Paramylodon from Rancho La Brea were so high that the population may represent the beginning of a speciation event that was nipped in the bud by the Pleistocene megafaunal extinction.
  • Joseph Peterson spoke about dinosaur paleopathology, and in particular on the use of 3D reconstructions of a hadrosaur vertebra with tooth marks on it (as well as theropod jaws) to determine the identity of the animal that bit the vertebra.  Turns out it was most likely a juvenile Tyrannosaurus.
  • My old officemate Jonathan Calede spoke about his dissertation work in the Cabbage Patch Beds of Montana.  The Cabbage Patch Fauna (named after a bar, not the creepy dolls, to paraphrase Jonathan) has been uncovered from several sites, which Jonathan found to be broadly similar in terms of geology and quality of preservation, suggesting that any trends observed between these sites represent genuine ecological patterns rather than taphonomic bias.
  • Nebraska's Shane Tucker discussed one of the coolest fossil sites of which I've ever heard: the Happy Jack Mine in the central part of the state.  The tunnels of the mine intersect infilled rodent burrows from the Miocene, allowing the 3D structures of these burrows to be observed.  On balance, the burrows most closely match those of ground squirrels, though gophers may have been responsible for some.  Shane and George Corner also presented talks about Miocene faunas from elsewhere in the state, underscoring the absurd richness of the Nebraska fossil record.
  • Ross Secord and his student Tom Baldvins both spoke about isotopic records across two important intervals of climate change: the Paleocene-Eocene Thermal Maximum and the glacial-interglacial cycles of the Pleistocene, respectively.  I was particularly interested in Baldvins' talk, which showed that C4 grasses were more abundant in the northern Great Plains during interglacial periods.  More intriguingly (to me, at least) his analysis of horse body size from the same sites showed a positive correlation with temperature (i.e., horses were larger in warmer climates).  Always nice to see another study that shoots holes in Bergmann's Rule, though I'd be curious to see if the trend would persist with a larger sample size and using tooth-based estimates of body size.
  • An entire session was devoted to the White River Group and its fossils, which was not only interesting in and of itself, but gave some great ideas for the design of the Sedimentology & Stratigraphy class I'll be teaching next year.  Particularly intriguing to me was Kurt Spearing's talk on the first evidence of inner ear bones in nimravids.  Ear morphology is hugely important in carnivore phylogeny, and I have high hopes that more nimravid ear ossicles will turn up in the coming years, which could potentially help determine where in the feliform tree these enigmatic animals belong.
  • I also spoke at the conference (on the humerus morphology of felids and whether or not it can be used to identify the huge cat that was present in the Late Miocene of western North America), but perhaps more importantly, for the first time I had a student presenting.  Laurel Perper discussed some of the early findings of our project comparing the morphology of the bizarre South American marsupial sabertooth Thylacosmilus, the subject of this month's upcoming Fossil Vertebrate of the Month feature.
Carnivore reconstructions by Mark Marcuson
I would be remiss if I finished this post without mentioning that, as expected, the University of Nebraska was an excellent host.  Besides pulling off a very well-run conference, Lincoln remains an excellent place to spend a few days (if nothing else, it's one of the only places in the northern Plains where you can reliably find good food and drink after 8:00).  As I always do when I'm in town, I spent some time in the University of Nebraska State Museum, home of, among many other things, the largest collection of fossil proboscideans in the world.  They were also featuring an exhibit on the paleoart of Mark Marcuson, whose murals I'd seen in the museum before but with whom I had been largely unfamiliar.  Another paleoartistic effort of which I'd previously been ignorant but that I visited this time on the suggestion of Nick Famoso is the mosaic on the floor of the Nebraska State Capitol (see picture above), which depicts reconstructions of fossils animals from trilobites to mammoths.  Any state that puts prehistoric life front and center in the rotunda of its capitol is a good one in my book, and as far as I'm concerned cements Nebraska's status of most fossily of fossiliferous states.

08 April 2014

Fossil (Gondwanan) Vertebrate(s) of the Month: Notosuchia

I'll be heading to the Southern Hemisphere twice this (northern) summer, in honor of which my Fossil Vertebrates of the Month between now and August will all be from Gondwana, the former southern continent of which Australia, South America, Antarctica, Africa, India, Madagascar, and New Zealand are the primary remnants.  I was going to start this series in May, but this recent publication inspired me to start this month.
Pakasuchus, among the most mammal-like notosuchians.
The traditional story of vertebrate life on land in the Mesozoic is a relatively simple one, particularly in regards to mammals (small and shrew- or rat-like according to this view), dinosaurs (diverse and dominant), and crocodilians (aquatic ambush predators, then as now).  The beauty of nature, of course, is that it is seldom simple, and one of the more exciting accomplishments of paleontology in recent decades has been the elucidation of the glorious complexity of ecosystems from the woefully misnamed "Age of Dinosaurs."  Several mammalian paleobiologists, spearheaded by Zhe-Xi Luo, have shown that mammals were much more diverse than had previously been thought (some of them even preying upon dinosaurs).  Even crocodiles, long used as the exemplar of a group that found its niche early on and succeeded by staying there, were not all swamp lurkers in the Mesozoic.  In fact, one group of Cretaceous crocodilians on the southern continents evolved to inhabit ecological roles generally associated with mammals today.  Known as notosuchians (literally 'southern crocodiles'), their most remarkable features can be found in and around the jaws.  Much has been made of the complex teeth of mammals and how this allowed them to diversify to take advantage of a wide variety of diets, but notosuchians show that our own class does not have a monopoly on such adaptations.  Unlike most reptiles, many notosuchians had heterodont dentition, as do mammals, and the wide ranges of niches into which the group evolved led to some of the strangest animals that have ever lived.  Some members of the group were likely predatory, making them at least superficially similar to living crocodilians, but other members of the group have been interpreted as omnivores or even herbivoresMalawisuchus likely processed food through a forward-backward motion of the jaw, Anatosuchus had a duckbill, Yacarerani had huge, procumbent incisors, and the eponymous Notosuchus may have had cheeks and a pig-like snout.  Not all bizarre adaptations among notosuchians were related to eating: as its name suggests, Armadillosuchus evolved interlocking, flexible armor that anticipated that evolved by armadillos millions of years later.