|Pakasuchus, among the most mammal-like notosuchians.|
08 April 2014
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.
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 herbivores. Malawisuchus 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.
03 March 2014
|Sharks jaws (C. megalodon at right)|
Florida Museum of Natural History
23 February 2014
|Conditions in what locals routinely assured|
me was the coldest Florida winter in ages
The State of Florida (Bronze)
|Sunset with gator, Lake Alice|
With all the development that has occurred in parts of Florida and a general lack of topography, it's easy to overlook the fact that the Sunshine State remains one of the great natural areas in North America. Florida wildlife is truly spectacular, which makes it a perfect place for a convention of natural scientists. The host hotel was buzzed by flocks of ibis, vultures, and sandhill cranes, while the pond just across the street was home to a little blue heron that seemed to be very fond of displaying its fish-spearing prowess. I made a couple of trips further into the UF campus, to Lake Alice, where nature puts on such a great show around sunset that you can't help but wonder why anyone ever bothered to build Disney World. Large flocks of waterfowl roost at the lake and return to their trees at dusk, just as the healthy population of alligators (and a few massive soft-shelled turtles) move to within a few feet of shore. The University maintains a colony of Mexican free-tailed bats nearby, and while watching them emerge from the bat houses is spectacular in and of itself, the local red-tailed hawks have figured out that the colony represents a chiropteran smörgåsbord, and the aerial show put on by the raptors and their evasive prey is "red in tooth and claw" nature at its finest. The fossil record of the state is no less impressive. The planners of NAPC took advantage of this by running several field trips to sites throughout the state. I was only able to go on one of these, to a phosphate mine east of Tampa that was rich in shark and ray teeth, dugong ribs, and even a few scattered horses molars. From what I heard of the other trips, they were equally productive, underscoring just how many fossils you can find when you work in a state composed entirely of sedimentary rocks. Of course, the classic allure of Florida is its climate, which was, for the most part, a wonderful distraction from the record-cold temperatures that we've been enduring in much of the country. Ironically, though, it's weather that hurt Florida in the final reckoning, as many flights down were delayed or cancelled due to snow in neighboring states and those of us that stuck around for a few days after the conference were treated to a spectacular and delay-inducing thunderstorm system (that, for the first time, allowed me to experience the pure terror of a zero-second delay between lightning bolt and thunderclap). However, even the arrival and departure chaos had a silver lining, at least for me. My flight down was cancelled and I was rerouted to Tampa, which gave me the opportunity to drive up the Gulf Coast past Crystal River, home of the largest concentration of manatees in the world and a display of cooperative hunting of mullet by dolphins and pelicans that made Gainesville's hawks look like amateurs. As far as the delay in my return to Iowa, well, any day not spent in the snow is a worthwhile one in my book.
The University of Florida (Silver)
|The Hall of Florida Fossils|
I heard from a few people that the UF paleo program saw NAPC as their coming-out party that would establish them as major players on the paleontology scene, both nationally and globally. I found this a little puzzling, as I'd already thought of them in this light for some time, but if this was their goal, they certainly succeeded. The opening event of the conference was held in the Florida Museum of Natural History and while it was under-attended due to delayed flights, the museum is an especially sparkly jewel in UF's crown. I am perhaps a bit biased, as the the exhibits heavily feature Neogene mammals, but I can think of few other places that so effectively combine classic, specimen-heavy displays with interpretation that puts those specimens in context and makes them valuable educational tools (this is even more true of the other exhibit halls, which seamlessly combined ecology and anthropology). At the end of the conference the vertebrate paleontology collections staff at the museum were kind enough to let me in on short notice to photograph cat humeri, in which they are exceptionally rich. In fact, they seem to be exceptionally rich in many types of fossils, from gators to ground sloths. Not only that, but for a collection as massive as UF's, the specimens are remarkably well-curated and organized, making it a pleasure to work there and an even more valuable resource for those of us who conduct collections-based research. In between the ice breaker and my collections visit, this meeting did nothing to alter my opinion that NAPC is the best-run conference in paleontology. Everything from the snacks provided to the registration process had clearly been well thought-out and was efficiently executed. When the aforementioned snowstorm along the East Coast reared its ugly head, the conference organizers rolled with the punches and accommodated presenters that missed their time slots as well as (or, in fact, better than) could be expected. No conference is perfect, and in this case the one flaw was the host hotel, which was isolated from the rest of Gainesville and was operated by staff that were either incompetent or possibly just inflexible. Like a fine Turkish rug, though, no conference should ever be completely perfect, and in any case NAPC can hardly be blamed for the hotel's shortcomings. On the off-chance that any of the organizers read this blog, let me just offer a hearty 'well done.' The 2009 NAPC in Cincinnati set the bar very high, and you met their challenge admirably.
My Fellow Paleontologists (Gold)
|Paleontologists in their element|
Probably the greatest thing about NAPC is that, unlike certain conferences (I'm looking pointedly at you, SVP), it embraces the diversity of backgrounds and interests among its attendees. Instead of shoehorning presenters into sessions based on the organisms they study, NAPC is organized by the overarching questions being asked by paleontologists and by the methods they use to answer those questions. This allows you to interact with people whose work might be related to your own but that you might not normally ever encounter, fulfilling the most important function of a conference: to get lots of paleontologists together to share ideas, collaborate, and advance the science. I always attend fewer talks at conferences than I should, but here are a few highlights of what was being presented this year:
- I was fortunate enough to be selected for a session on large-scale bias and fidelity of the fossil record, a crucially important topic to understand because of its implications for conservation paleobiology, an emerging discipline that focuses on using the fossil record to predict future ecological change. The keynote talk in the session, by Matthew Kosnik, showed that due to mixing of sediments at sites along the Great Barrier Reef, interpreting changes through time in "normal" marine communities may not be as straightforward as it might seem. I followed Josh Miller's talk on comparing live and dead assemblages in Amboseli National Park, Kenya just as I often used to follow his solos back in high school when we played in the same jazz band. Josh is an even better taphonomist than a trumpeter, which is saying something, and his talk was one of the highlights of NAPC. His findings suggest that the traditional view that body size is a huge, if not dominant, determining factor in the preservation of fossils mammals is not necessarily true. In fact, the least well-preserved taxa in his sample were not small mammals as might be expected, but rather cavity-dwelling predators that are active at unusual times during the day, suggesting that when we think about bias in the fossil record we should be thinking in more nuanced ecological terms.
- Rebecca Terry (bizarrely, another graduate of the same fairly small high school as Josh and myself) spoke on small mammal communities in the Great Basin. Because most of the small mammals present in the Pleistocene are extant today, they are often the focus of conservation paleobiological studies of change through time. However, Rebecca suggests that in fact a major ecological restructuring took place in the Great Basin characterized by the preponderance of generalist taxa that may reflect the influence of humans in the area and that underscores the importance of remembering that conditions in the past- including the very recent past - are not always perfect analogs for those of the present and future.
- Both Felisa Smith and Jonathan Marcot spoke on mammal body size, a topic near and dear to me. Smith used body size as an example of an ecological trait that can be studied across large spatial and temporal scales through what she referred to as a "macroscope." Marcot provided a great example of a case study in macroscopic analysis by looking at body size through time in several groups of ungulates and found a roughly synchronous increase in body size in the vicinity of the Oligo-Miocene, suggesting the importance of environmental factors in driving body mass.
- Of all the sessions at NAPC, none was more interesting to me than the one focusing on the evolution and grasslands and grazers and that that neatly integrated talks by researchers working on vertebrates, plants, soils, and geological processes. The recurring theme in this session was that one of the oldest "just-so" stories in paleontology is wrong. Many herbivorous mammals have high-crowned (hypsodont) teeth, and this was long assumed to be an adaptation to eating grass, which contains large amounts of silica in its blades and consequently wears down teeth faster than would a diet of leaves. Paleontologists have been poking holes in this scenario for years, but the flood gates have really opened recently. Several talks by Caroline Strömberg and her colleagues detailed the timing of grassland appearance in the Americas and showed that there is no correlation with the evolution of hypsodonty. Sam Hopkins showed that herbivorous rodents and lagomorphs evolved hypsodonty well before ungulates, suggesting that a grazing diet alone cannot account for high-crowned teeth. Deborah Rook and Richard Madden both looked at mechanisms by which grit, likely an important factor in the evolution of hypsodonty, could be introduced into grassland environments, and Brian Beatty (standing in for Matt Mihlbachler) addressed the phylogenetic and ecological factors that should be taken into account when studying tooth wear in herbivores. Another perspective on hypsodonty was provided by Nick Famoso (presenting in the "Blizzard Session"), who showed that within horses there seems to be no connection between hyposdonty and enamel complexity.
- The grassland session ended with a talk by Lars Werdelin who, along with Mikael Fortelius, is developing a project that will look at the top-down influence of predators in their ecosystems through time. Several major changes have taken place in predator guilds through the Cenozoic, such as the replacement of creodonts by carnivores in North America and the arrival of placental mammals, including carnivores, in South America but studies of how such events have effected other mammals within paleocommunities are lacking. Teasing apart biological interactions such as predation from other potential causal factors can be difficult, but if anyone is up to the task it would be Werdelin and Fortelius and I am enormously excited to see what happens as this project unfolds.
- Probably the most cutting-edge session focused on the use of 3-D imaging in paleontology. Several talks in this session fell towards the implementation end of the spectrum, about which I am not really able to comment intelligently, but both Aaron Wood and Dave Polly provided really interesting examples of how 3-D scans can augment paleoecological analyses.
At this point, my Olympics analogy founders a bit because traditionally this is where a national anthem would be played, and of course there is no anthem for paleontologists...or is there?
04 December 2013
paleoecologist, interactions between animals and their environments are my stock-in-trade. For the most part, paleoecologists study these interactions by observing trends through time in the variables of interest in search of macroscopic patterns. Every now and then, though, a fossil turns up that captures (or at least appears to capture) an interaction between an individual and some aspect of its environment (usually another animal). The most famous examples of this are, unsurprisingly, saurian: I had the opportunity to view the amazing Mongolian "Fighting Dinosaurs" when they were on display in New York a few years back, and another pair has made headlines for all the wrong reasons in recent weeks. However, no specimen provides as good an example of both the power and the pitfalls of "fighting fossils" as a skull in the University of Nebraska State Museum. It is a specimen of Nimravus brachyops, a member of the eponymous Nimravidae. Nimravids are a fascinating group of carnivores in their own right: they are mid-sized saber-toothed predators that were particularly abundant in the Oligocene and are nearly indistinguishable from cats but are probably closer relatives of civets. This specimen, however, is of interest from more than just a scientific point of view. It was found with a canine embedded in the humerus of another N. brachyops, showing that the two individuals had died fighting. That, at least, was the conclusion of the field crew that first uncovered the specimen. This crew included a young Loren Eiseley, who would go on to become one of the most prominent naturalists of the 20th Century. Eiseley was so impressed by the specimen that it inspired him to write one of his most famous poems, 'The Innocent Assassins.' The picture painted by the fossils and by the poem is certainly dramatic, but is it accurate? Paleontology has long been plagued by studies that put good stories in front of the evidence of the fossil record and, unfortunately, this may be one of them. First of all, there is no irrefutable evidence that more than one individual was present (in paleontological parlance, the Minimum Number of Individuals is 1, meaning that it is impossible to disprove that both bones came from the same animal). Of course, no one would suggest that the nimravid bit through its own arm. However, it is possible that the humerus and the canine were driven together after death, either during transport or, probably more likely, during burial. As others have observed, this latter scenario is supported by the fact that the canine, while broken towards its tip, is largely intact. One of the major paradoxes of saber-toothed predators is that elongated canines are, for the most part, exceptionally brittle and would have broken remarkably easily if too much stress were applied to them. It beggars belief that this Nimravus had canines robust enough to not only puncture bone but to remain mostly intact during the struggle that would have followed. Perhaps the Nebraska specimen really does represent a death struggle, but the balance of probability is that taphonomy, not paleoecology, provides the explanation for the association between the two bones. For those of you who find this depressingly banal, I hasten to add that this does not mean that nimravids never fought. A well-known specimen from South Dakota seems to represent a Nimravus skull that has been punctured by the saber of the smaller nimravid Eusmilus, and a talk at this year's Geological Society of America Meeting suggested that such injuries might be more common than previously thought. Nimravids may very well have been preternaturally pugnacious, but for all of Eiseley's eloquence, the true drama of the "Innocent Assassins" specimen lies not in the moment of death but in the evolutionary and ecological story into which the fossil fits.
13 November 2013
|Holyoke Stegomastodon Tusk|
Denver Museum of Nature & Science
Relevance to my family's history is not the only reason I'm featuring Stegomastodon this month. It was among the last of the gomphotheres, one of the most prolific (though probably paraphyletic) groups of proboscideans (despite what the name might suggest, it was neither a close relative of the North American mastodon nor of the Asian Stegodon). Elephants and their relatives are one of the great triumphs of mammal evolution, due in large part to their ability to disperse widely, and Stegomastodon represents an especially important milestone in this history: it was one of only two proboscidean genera to colonize South America during the American Biotic Interchange (the other being Cuvieronius, also a gomphothere). Instead of being just an isolated specimen from eastern Colorado, then, the Holyoke Stegomastodon was part of the last great success story of a once diverse group of proboscideans, a story that unfolded not just on the Great Plains, but across Panama and into the Pampas of South America.
07 November 2013
04 July 2013
John Day Fossil Beds National Monument