Fossil Vertebrate of the Month: Nothrotheriops

Nothrotheriops in the Nevada State Museum, Las Vegas
John Orcutt, 2011

Sloths have figured prominently on this blog lately (see my posts on Megatherium and Megalonyx from the past year).  That theme continues this month with Nothrotheriops, a genus of ground sloth that has been found throughout the southwest US and northern Mexico (and at one site in Florida), including within the Phoenix metro area, site of this month's Western Association of Vertebrate Paleontologists annual meeting.  There are two known species: N. texanus and its apparent descendant N. shastensis, both of which lived during the Pleistocene.  While my previous sloth posts have focused primarily on the taxon's place in the history of science, Nothrotheriops is remarkable as an example of how paleontological data can inform our knowledge of both paleo- and modern ecology.  This is in large part because it lived primarily in arid climates and apparently frequented caves, possibly even using them as sites for dens, meaning that Nothrotheriops has a fantastically high preservation potential and that preserved soft tissue and dung are not uncommon.  Analysis of the dung has been particularly informative, providing direct evidence of the plants eaten by the sloth (primarily desert globemallow) as well as of interactions with other organisms (fungus gnat larvae fed on vegetable matter in the dung, which also contains traces of parasitic nematodes).  Perhaps the most remarkable aspect of Nothrotheriops ecology, though, is its connection to Joshua trees.  Despite being icons of the Mojave Desert, Joshua trees may be doomed to extinction (or at least widespread local extirpation) due to their extremely slow dispersal rate keeping them from shifting their range in response to climate change.  Based on relatively large amounts of Joshua tree material having been found in Nothrotheriops dung, it is not unreasonable to assume that the sloths, in eating and excreting seeds, served as important dispersal agents for the trees.  A recent paper has suggested that the extinction of sloths and other desert megafauna made the Joshua tree an effectively immobile species.  While this hypothesis awaits a rigorous paleontological test, if it proves to be correct (as seems very likely) it will have important implications for the conservation of Joshua trees, underscoring the importance of fossil data in predicting and mitigating the effects of future climatic change.

Fossil Vertebrate of the Month - Lystrosaurus

One hundred years ago this month - on January 6th, 1912 - Alfred Wegener presented his idea that the continents had once all been joined (in a supercontinent he termed Pangaea) and were slowly floating apart as part of a process he called continental drift.  His hypothesis was largely derided at the time, but would eventually evolve into plate tectonics, which is now the unifying theory of geology.  Numerous lines of evidence were brought together to establish the validity of plate tectonics, but among the most convincing was the presence of remarkably similar fossils on distant continents.  Perhaps the most famous of these organisms was the Permo-Triassic dicynodont Lystrosaurus.  First described from South Africa, the discovery of Lystrosaurus fossils in Antarctica in the 1960s showed beyond a reasonable doubt that the two continents must have been joined (it has subsequently been uncovered in India, East Asia, and Europe, driving home the reality of plate tectonics even further).  Besides its utility as a biogeographic marker, Lystrosaurus is remarkable for being one of the few survivors of the Permian-Triassic Extinction, which, by some estimates, wiped out over 90% of life on Earth.  Why it was able to survive this cataclysm and to prosper in its aftermath is something of a mystery, as in many ways Lystrosaurus is a very unimpressive animal (they are often referred to as the pigs of the Triassic).  In fact, my original dissertation project (before I was romanced by its distant mammalian relatives) was to be a test of the hypothesis that Lystrosaurus, as a burrowing animal, was adapted to the low-oxygen conditions that may have characterized the Early Triassic.  In another Oregon-related note, the picture above is of a model from Prehistoric Gardens, south of Coos Bay, one of the more atmospheric and well-preserved "dinosaur parks" in the world.

Fossil Vertebrate of the Month: Shonisaurus popularis

Earlier this month, the Society of Vertebrate Paleontology held its annual meeting in Las Vegas.  The conference logo - one of the best I've ever seen for an SVP meeting - featured the ichthyosaur Shonisaurus, Nevada's state fossil (shown in the picture at left in the new Nevada State Museum, Las Vegas).  Shonisaurus was a remarkable animal.  Dating from the Late Triassic, it was not only one of the earliest ichthyosaurs, but at 15 meters in length was also among the biggest (the largest known ichthyosaur was the Triassic Shastasaurus, which has been reported from Oregon, British Columbia, and Northern California, among other places).  Shonisaurus skeletons have been found in large numbers - and in remarkably good condition - in Berlin-Ichthyosaur State Park southeast of Reno, making it among the best-known early ichthyosaurs.  The concentration of skeletons at the locality has been interpreted several different ways through the years.  It was originally thought to represent a stranding site, but the lithology and paleontology of the site indicate a deep water environment.  It has also been interpreted as evidence of an ichthyosaur breeding ground, though the lack of juvenile specimens contradicts this hypothesis.  The generally accepted explanation for the bone bed is that it represents an area of upwelling that would have brought nutrients up from the deep sea, supporting a diverse ecosystem in which Shonisaurus would have been the top predator.  Unfortunately, Shonisaurus has also been the subject of an exceptionally high-profile and exceptionally shoddy study this year that used the arrangement of skeletons as "evidence" of an exceptionally intelligent cephalopod; the readiness with which a talk on the subject was accepted by the Geological Society of America and the eagerness with which it was reported by the media are black eyes for paleontology and for scientific journalism.

The Manis Mastodon

While growing up in Seattle, I often lamented the lack of dinosaurs from the Pacific Northwest, but I always took some solace in the fact that we had some pretty cool mammal fossils.  I was a regular visitor to the Burke Museum to see the Blue Lake Rhino and the Sea-Tac Sloth, and my family indulged me enough to take me on trips to Ginkgo State Park, Republic, and the John Day Fossil Beds.  One of my particular favorite Northwest fossils was the Manis Mastodon, found near the town of Sequim, on the Olympic Peninsula, because, as a proboscidean, it was big, and therefore akin to the dinosaurs I so desperately wanted to study.  Now, of course, things have come full circle, and I'm living in the Northwest again and studying mammal paleontology.  I have a new appreciation for all the fossils I visited as a child (the John Day fauna has, in fact, become a huge part of my research), and it turns out that one of my old favorites was even more important than I realized.  The Manis Mastodon wasn't just big: it turns out that it's one of the only specimens in North America that preserves evidence of humans butchering a mastodon.  It had long been suspected (at least by some) that a bone point embedded in one of the mastodon's ribs was a broken-off projectile point, which would imply that humans not only scavenged mastodon carcasses, but might have actively hunted them as well.  This hypothesis was recently put to the test by a group of researchers that includes WSU's Carl Gustafson, the scientist that conducted the initial study of the site.  Scans of the rib confirm this hypothesis, but perhaps the most exciting finding of the study was that the Manis site was far older than had been expected: about 13,800 years old.  This revelation has two major implications.  First, it supports the evidence of the so-called "Kelp Highway" hypothesis (the main research focus of Oregon's own Jon Erlandson) that humans populated the Americas by travelling south along the West Coast.  Second, it suggests that humans were hunting large animals prior to the development of stone Clovis points, which may itself have implications for the extinction of the North American megafauna.  The moral of this story?  Never let anyone (even a younger version of me) tell you that there aren't any interesting fossils in the Northwest; as long as our region continues to yield finds like the Manis Mastodon, there will be plenty to keep paleontologists here busy for a long time.

Addendum: Adding to the Manis Mastodon's Northwest cred, Knute Berger, my favorite Seattle journalist has supplied a brief article on the subject.

Fossil Vertebrate of the Month - Terror Bird

This is the largest group of organisms I've ever featured as a FVOTM, but given that we're coming up on Halloween, it seemed appropriate to spotlight a family whose common name is based on how terrifying they were.  Terror birds (or, more correctly, phorusrhacids), represented by the LA County Museum's mount of Paraphysornis in the picture at left, were a group of giant, flightless birds related to living seriemas, most of which have been uncovered in South America.  Flightless birds are not unusual, as anyone who's seen an ostrich, emu, or rhea (or fossils of elephant birds, moas, or mihirungs) can attest.  However, phorusrhacids were different in one key respect: they were carnivorous.  Carnivory has been suggested for some other land birds - chief among them the Eocene Gastornis, itself a possible terror bird ancestor - but the huge size, robust build, and raptor-like beaks of phorusrhacids leave no doubt.  In fact, the near absence of large mammalian carnivores in South America for most of the Cenozoic indicates that the top predator niche on that continent was occupied by terror birds (they would have preyed upon one of the strangest herbivore faunas in the world, composed of, among other things, meridiungulates, xenarthrans, and - somewhat inexplicably - platyrrhine primates and hystricomorph rodents).  Phorusrhacids were key players in the American Biotic Interchange; once thought to have gone extinct when mammalian carnivores (including the iconic Smilodon) moved in from the north, it is now known that terror birds actually expanded onto the Gulf Coastal Plain in North America, where they were represented by Titanis, one of the largest birds ever to have lived (though it was not the largest phorusrhacid - that honor is currently bestowed on the recently-described Kelenken from Argentina).

Fossil Vertebrate of the Month: Megalonyx jeffersoni

This month's (somewhat belated) fossil vertebrate is a long-time favorite of mine: Megalonyx jeffersoni, a Pleistocene ground sloth.  The reasons for it being one of my favorites are prosaic enough: there was a skeleton of one in Seattle's Burke Museum while I was growing up (a specimen that was discovered during the construction of Sea-Tac Airport, which I always felt would make it a good candidate for Washington State Fossil, an honor that's since been bestowed on the Columbian mammoth).  Ground sloths are one of the great evolutionary success stories to come out of South America, having been among the first animals from the formerly island continent to expand into North America after the formation of the Isthmus of Panama about 3 million years ago (ground sloths actually seem to have made the jump to North America well before the isthmus was fully formed, suggesting that they, like modern sloths, were very capable swimmers).  Ground sloths thrived in North America until the Pleistocene megafaunal extinction, around 13,000 years ago, that also sounded the death knell for mammoths, horses, camels, and many other types of mammal on the continent.  Megalonyx has the distinction of being the only fossil vertebrate to have been described by a President of the United States: Thomas Jefferson, who described a specimen from a cave in West Virginia as a kind of lion.  The great anatomist Caspar Wistar subsequently reidentified it as a sloth, named the species after the then ex-president, and is thought to have suggested to Meriwether Lewis that he keep a weather eye open for living megafauna, such as Megalonyx, during his expedition west with William Clark.

Orcutt & Hopkins, 2011

It's been a long time coming, but as of today, my first paper is officially published.  It's in this month's Journal of Vertebrate Paleontology and has the thrilling title 'The canid fauna of the Juntura Formation (Late Clarendonian), Oregon.'  It's far from groundbreaking work, as most of it is a redescription of misidentified specimens, but it does have its noteworthy elements.  It includes the description of a jaw of the giant dog Epicyon saevus found during our lab's field work in 2008.  It provides information on the postcrania of the even more giant E. haydeni and the much smaller (but previously unknown from the Northwest) Carpocyon.  Perhaps most importantly, it's the first publication to come out of the Hopkins Lab's Juntura Project.  The Juntura Basin east of Burns in southeast Oregon was the research focus of the pioneering paleoecologist J. Arnold Shotwell (also of the U of O) until the 1970s, but has been largely neglected since Shotwell left the field.  Our lab's field work in the area has been the first concerted research project there in nearly forty years, and if nothing else my paper stands as the first fruits of what will hopefully (and presumably) be a very fruitful paleontological endeavor.