19 August 2015

Fossil Vertebrate of the Month: Mammuthus columbi

The Latah Mammoth looming above other Pleistocene megafauna
The Field Museum
There are many magnificent fossils from the Northwest, from the Cambrian wonders of the Burgess Shale to the Cenozoic animals and plants of the John Day Basin.  Many of these specimens are visually spectacular, quite a few have figured into major debates in paleontology, and all have a fascinating story to tell, but it is unlikely that any have as large an audience as a mammoth uncovered over a century ago outside of Spokane.  The specimen in question was found in a bog on the property of the Coplen Family along Latah Creek in 1876.  Following its excavation, the fossil began an odyssey that has been eloquently described by writer Jack Nisbet.  Along the way, it crossed paths with no less a figure than Thomas Condon, the father of paleontology and geology in the Northwest, and was identified first, incorrectly, as a woolly mammoth and later as a Columbian mammoth, Mammuthus columbi.  In the end, the Latah Mammoth landed in Chicago, where it was owned by the Chicago Academy of Sciences, displayed at the World's Columbian Exhibition, and was finally reposited in the Field Museum.  It remains on display there today, one of the more impressive specimens in one of the world's more impressive fossil collections.  Last year alone, more than a million visitors had an opportunity to view this former resident of the Palouse, making it probably the most visited fossil ever uncovered in the Northwest.  While they were far from the first proboscideans in North America, mammoths were tremendously successful after migrating from Asia at the beginning of the Irvingtonian Land Mammal Age.  Unlike woolly mammoths, which had a holarctic distribution, Columbian mammoths were endemic to North America, and their phenomenal success is attested to by a rich fossil record from the edge of the continental ice sheets to Central America.  While the Latah Mammoth is the most familiar mammoth to have been uncovered from the Northwest, several other fossils of note have been uncovered here that have received varying degrees of scientific and popular attention.  The only specimen to achieve anything near the fame of the Latah Mammoth is the Seattle Mammoth excavated early last year.  The specimen is just a tusk, considerably less impressive on the surface than the Latah skeleton.  However, rather than having been found along a remote creek in eastern Washington, it was uncovered while constructing a new office building in the South Lake Union "neighborhood" of Seattle.  The finding of the remains of so iconic an animal in the midst of one of the fastest-growing parts of a major city and a very successful educational campaign by the Burke Museum have done much to generate enthusiasm for and appreciation of paleontology among Seattleites.  More recently, mammoths were among the animals analyzed as part of an study establishing a chronology of megafauna in the Willamette Valley following the devastation of the Missoula Floods, allowing a more rigorous analysis of the impacts of human activity and climate change than had previously been possible in the region.  Mammoths have long been among the more charismatic of extinct animals, and their popularity was recognized in Olympia in 1998 when a 2nd grade class from Cheney petitioned the state legislature to name Mammuthus columbi the Washington State Fossil, making it an official symbol of the Evergreen State along with apples, hemlocks, and rhododendrons (and, for that matter, petrified wood).

10 July 2015

Fossil Vertebrate of the Month: Bretzia pseudalces

Bretzia pseudalces antlers (on an Odocoileus skull)
From Gustafson (2015)
As I'm returning to blogging and to life as a Washingtonian after a hiatus from both, it seemed appropriate to feature an animal first described from the Evergreen State and that was recently the subject of a monograph in a journal emerging from a long hibernation.  The animal in question is Bretzia pseudalces, a deer uncovered from the Pliocene Ringold Formation of eastern Washington (while other species of Bretzia have been found across western North America, B. pseudalces is known from the Pasco Basin, along the Columbia River north of the Tri-Cities).  The Pliocene age of the Ringold Formation is significant: while deer are abundant across the continent today, they are in fact relatively recent arrivals in North America.  Much as another iconic American animal, the bison, would do in the Pleistocene, deer migrated to the continent only at the very end of the Miocene, just over 5 million years ago (as an aside, of the animals mentioned in 'Home on the Range,' only the pronghorn "antelope" has a deep evolutionary history on the North American plains).  This makes B. pseudalces one of the oldest cervids in North America and part of the first radiation of New World deer.  Superficially, it would have appeared similar to another member of this radiation, the still-extant Odocoileus.  In fact, several features differentiate the two genera, with the most readily apparent of these being the antlers.  While modern white-tailed and mule/black-tailed deer have antlers that are a series of branching tines, the antlers of Bretzia were palmate (that is, shaped like the palm of a cupped hand, as in modern moose).  Precisely how Bretzia was related to other deer remains unclear, though hopefully this will change with future research; an assessment of how the genus fits into the broader picture of cervid evolution could, among other things, help refine our understanding of how immigrant taxa respond to new environments on a large scale, a non-trivial thing in an age during which species are shifting their ranges and being introduced into new environments at unprecedented rates.  Fortunately, the groundwork for such a study has been admirably laid by the University of Oregon's Eric Gustafson, who earlier this year published a monograph on the anatomy and taxonomy of B. pseudalces in Volume 25 of the UO Museum of Natural & Cultural History Bulletin.  This makes the monograph remarkable not only because of Gustafson's scholarly achievement, but because Volume 24 was published in 1983.  Given that the earlier run of the bulletin included such highlights as the description of the saber-toothed salmon and a number of papers by the great Oregon paleontologist and pioneering paleoecologist J. Arnold Shotwell, its reemergence is both exciting and a testament to the vibrancy of paleontology in the Northwest.

25 June 2015

Kelipi

The title of this post means 'Return' in Chinook Jargon, a mix of Native American languages, French, and English that served as the lingua franca of the Northwest from roughly the period of European contact through the end of the 19th Century.  As astute as my readership is, I'm sure you've also noticed that the title of the blog is now in Chinook Jargon as well and that the appearance of the whole page has changed.  Why these changes and why the use of a somewhat obscure language?  Well, just as life, climate, and Earth itself change through time, this blog has evolved since first being founded.  Think of its first iteration, The Oregon Trail, as its Paleozoic, a long interval during which it looked fairly different from its current form but that laid the foundation for what has come since.  The real Paleozoic, of course, ended with Permian Extinction, in turn ushering in the Mesozoic; the epochal event in this blog's history was my move to Cornell College, marking its change to The Mammoth Prairie.  The sudden end of the Mesozoic was marked (and probably caused) by a bolide impact; the similarly unexpected event in my life was a change of scenery from Iowa to Gonzaga University in Spokane.  This has ushered in the third stage in the history of my blog, and just as the Cenozoic is the most interesting period of Earth history, I trust the current iteration of my blog will reach new heights over the coming months.  So much for all the changes and for my recent hiatus; so why all the Chinook Jargon?  In part, because I was returning to the Northwest, I wanted something in keeping with the region's history.  While I've lived a good portion of my life west of the Cascades, my research and current job are both centered in the dryer country to the east, so I wanted to pick something with relevance to both the Pacific and Inland Northwest.  At its peak, Chinook Jargon was spoken widely from the Rockies to the Pacific and from Alaska to the "State" of Jefferson, nicely approximating the boundaries of the Great Northwest.  Beyond simply being locally relevant, though, my choice of a Chinook Jargon name reflects a subtle shift in my goal for this blog.  As the insidious spread of climate change denialism and creationism attest, public understanding of natural science are at or near an all time low.  I and other paleontologists have long viewed our field as a "gateway science" to biology, geology, and even climatology, but in an age where science - at least in the US - is effectively under attack, our role as scientific ambassadors has become increasingly important.  In light of this, my career has drifted more and more towards education and I intend for this blog to follow suit.  Just as I still conduct research of my own, I'll still be posting Fossil Vertebrates of the Month and sharing my thoughts on recent publications from time to time, but there are many other blogs out there that do so more frequently, more eloquently, and with more authority than mine.  I hope that as a research scientist writing about education and fostering appreciation for the natural sciences I will be filling a niche that is less populated and very important.  Just as I hope that this blog will serve as a useful resource for those who want to establish a dialog between scientists and non-scientists, Chinook Jargon was a language that (probably) first developed to facilitate discourse between the multilingual nations of the Northwest and later evolved to allow communication between these nations and European interlopers, making it an appropriate choice for naming this blog.
After all this, though, you may still be wondering what the new title means.  As a trade language, words such as 'paleontology' and 'fossil' are unsurprisingly absent from Chinook Jargon.  However, there is a word for knowing or understanding (kumtuks) and a word for yesterday (tahlkie); put them together and you get "understanding yesterday" (or, if you want to play fast and loose with translation, "understanding the past"), a phrase that not only sums up the goal of my research, but describes what I aim to foster through education.  It's also a nod to a quote from Confucius that's one of my favorites because it so succinctly makes the case for why we should care about paleontology and other historical sciences: "Study the past if you would define the future."

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!