Monday, September 27, 2010

New Horned Dinosaurs!

Thanks to a recent spate of papers describing new species, 2010 has been unofficially dubbed “the year of horned dinosaurs.” This past week, my colleagues (Mark Loewen, Andrew Farke, Eric Roberts, Joshua Smith, Catherine Forster, and Alan Titus) and I added two more to the list, formally announcing a pair of amazing ceratopsids discovered in Grand Staircase-Escalante National Monument, southern Utah. The giant plant-eaters were inhabitants of the “lost continent” of Laramidia, formed when a shallow sea flooded the central region of North America, isolating eastern and western portions of the continent for about 27 million years during the Late Cretaceous Period. The newly discovered dinosaurs, close relatives of the famous Triceratops, were announced in PLoS ONE, the online open-access journal produced by the Public Library of Science.

The bigger of the two new dinosaurs, with a skull 2.3 meters (about 7 feet) long, is Utahceratops gettyi. The first part of the name combines the state of origin with ceratops, Greek for “horned face.” The second part of the name refers to Mike Getty, paleontology collections manager at the Utah Museum of Natural History and the discoverer of this animal. Mike has been the driving force behind the UMNH paleo field program, and it is a great pleasure to be able to honor him in this way. In addition to a large horn over the nose, Utahceratops has short and blunt eye horns that project strongly to the side rather than upward, much more like the horns of modern bison than those of Triceratops or other ceratopsians.

Second of the new species is Kosmoceratops richardsoni. Here, the first part of the name refers to kosmos, Latin for “ornate,” and ceratops, once again meaning “horned face.” The latter part of the name honors Scott Richardson, the volunteer who discovered two skulls of this animal. In contrast to most scientific disciplines, volunteers make a major, fundamental contribution to paleontology, helping to find and excavate specimens, prepare and curate them in museum collections, and sometimes do the research. Scott Richardson has been a one-man fossil-finding powerhouse in GSENM, discovering stunning new specimens for about a decade.

Like Utahceratops, Kosmoceratops has sideways oriented eye horns, although much longer and more pointed. In all, Kosmoceratops possesses a total of 15 horns—one over the nose, one atop each eye, one at the tip of each cheek bone, and ten across the rear margin of the bony frill—making it the most ornate-headed dinosaur known. This ancient beast is one of the most amazing animals known, with a huge skull decorated with an assortment of bony bells and whistles. For obvious reasons, we avoided use of the term “horniest dinosaur” as a descriptor when announcing this animal. The media, it seems, had no such reluctance and immediately jumped on the opportunity.

Much speculation has ensued about the function of ceratopsian horns and frills, from fighting off predators to recognizing other members of the same species or controlling body temperature. Nevertheless, the dominant—and, to my mind, most likely—hypothesis is that these features functioned first and foremost to enhance reproductive success. Certainly most of these exaggerated bone structures of dinosaurs—including hooks, horns, crests, bosses, and spikes—would have made poor weapons to fend off predators. It’s far more probable that they were used to intimidate or do battle with rivals of the same sex, as well as to attract individuals of the opposite sex. Best we can tell, both males and female ceratopsid dinosaurs had horns. But this relative lack of sexual differences does not take away from the mate competition hypothesis; females of large-bodied (> 300 kg), gregarious, open-living mammals alive today, like bison and caribou, also tend to have headgear similar to that of males, likely to reduce the risk of being preferentially selected by predators.

The dinosaurs were discovered in sediments of the Kaiparowits Formation within Grand Staircase-Escalante National Monument. GSENM encompasses almost two million acres of high desert terrain in south-central Utah. This vast and rugged region, part of the National Landscape Conservation System administered by the Bureau of Land Management, was the last major area in the lower 48 states to be formally mapped by cartographers. Today GSENM is the largest national monument in the United States, and now of the country’s last great, largely unexplored dinosaur boneyards.
For most of the Late Cretaceous, exceptionally high sea levels flooded the low-lying portions of several continents around the world. In North America, a warm, shallow sea called the Western Interior Seaway extended from the Arctic Ocean to the Gulf of Mexico, subdividing the continent into eastern and western landmasses, known as Appalachia and Laramidia, respectively. Whereas little is known of the plants and animals that lived on Appalachia, the rocks of Laramidia exposed in the Western Interior of North America have generated a plethora of dinosaur remains. Laramidia was less than one-third the size of present day North America, approximating the area of Australia.

Most known Laramidian dinosaurs were concentrated in a narrow belt of plains sandwiched between the seaway to the east and mountains to the west. Today, thanks to an abundant fossil record and more than a century of collecting by paleontologists, Laramidia is the best known major landmass for the entire Age of Dinosaurs, with dig sites spanning from Alaska to Mexico. Utah was located in the southern part of Laramidia, which has yielded far fewer dinosaur remains than the fossil-rich north. The world of dinosaurs was much warmer than the present day; Utahceratops and Kosmoceratops lived in a subtropical swampy environment about 100 km from the seaway. It’s strange to contemplate giant dinosaurs making a living in a place that shares much in common with a Louisiana swamp, but that’s the emerging picture.

Beginning in the 1960’s, paleontologists began to notice that the same major groups of dinosaurs seemed to be present all over this Late Cretaceous landmass, but different species of these groups occurred in the north (for example, Alberta and Montana) than in the south (New Mexico and Texas). This finding of “dinosaur provincialism” was very puzzling, given the giant body sizes of many of the dinosaurs together with the diminutive dimensions of Laramidia. Currently, there are five giant (rhino-to-elephant-sized) mammals on the entire continent of Africa. Seventy-six million years ago, there may have been more than two dozen giant dinosaurs living on a landmass about one-quarter that size. How could so many different varieties of giant animals have co-existed on such a small “island continent?” One option is that there was a greater abundance of food during the Cretaceous. Another is that dinosaurs did not need to eat as much, perhaps because of slower metabolic rates intermediate between those of modern day lizards and crocodiles on the one hand, and mammals and birds on the other. Whatever the factors permitted the presence of so many dinosaurs, it appears that some kind of barrier near the latitude of northern Utah and Colorado limited the exchange of dinosaur species north and south. Possibilities include physical barriers such as mountains or, more likely, climatic barriers that resulted in distinct northern and southern plant communities. Testing of these ideas have been severely hampered by a dearth of dinosaurs from the southern part of Laramidia. The new fossils from GSENM are now filling that major gap.

During the past decade, crews from the University of Utah and several partner institutions (e.g., the Utah Geologic Survey, the Raymond Alf Museum of Paleontology, and the Bureau of Land Management) have unearthed a new assemblage of more than a dozen dinosaurs in GSENM. In addition to Utahceratops and Kosmoceratops, the collection includes a variety of other plant-eating dinosaurs—among them duck-billed hadrosaurs, armored ankylosaurs, and dome-headed pachycephalosaurs—together with carnivorous dinosaurs great and small, from “raptor-like” predators to mega-sized tyrannosaurs (not T. rex but rather its smaller-bodied relatives). Also recovered have been fossil plants, insect traces, clams, fishes, amphibians, lizards, turtles, crocodiles, and mammals, offering a direct glimpse into this entire ancient ecosystem. Most remarkable of all is that virtually every identifiable dinosaur variety found in GSENM turns out to be new to science, offering dramatic confirmation of the dinosaur provincialism hypothesis. Previously, our team has described two other dinosaurs from GSENM: the giant duck-billed hadrosaur Gryposaurus monumentensis and the raptor-like theropod Hagryphus giganteus. Several other animals are still under study, and will be announced in the future.

Without doubt, however, many more dinosaurs remain to be unearthed in the Western Interior of North America, once part of the island continent of Laramidia. Equally certain is the fact that some of those dinosaurs will be found within the remote canyons and badlands of GSENM. So stay tuned! (Oh, and for any fans of Dinosaur Train out there, plans are to feature Kosmoceratops early in the second season of episodes!)

Acknowledgements: I would like to express sincere thanks to the Bureau of Land Management and to the National Science Foundation, the pair of federal organizations that supplied the bulk of the funding for this project. Thanks also to the Utah Museum of Natural History for a decade of devoted support, and to all the volunteers and students who worked on this project.

Image Credits:
All dinosaur artwork, both skull images and fleshed out head reconstructions, were skillfully executed by our Italian colleague and friend, Lukas Panzarin. Reconstruction of Late Cretaceous North America by Ron Blakey (http://jan.ucc.nau.edu/~rcb7/RCB.html).

Additional Materials:
Check out the video that describes this story.

7 comments:

  1. Provincialism, territoriality? Species duration, anagenesis? Incredible new species and so many more being prepped and described as we speak. It's absolutely astonishing and just shows that no matter how much we know, there's still an enormous amount that we don't know.
    The more we learn, the less we understand (or is that a dichotemy in terms?). Absolutely awesome.

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  2. Scott, I can buy defense not being a primary means of selection (in fact, I think it likely), but I think many underestimate the utility of those kinds of structures for defensive purposes, even if they weren't primarily selected for that basis. In extant horned or antlered herding animals, observations have shown that a. standing still and b. keeping one's head towards a predator (that is, when it does have horns--for females without, that much is a very bad idea ;-) ) is far more likely to lead to survival than the oft suggested 'running away' idea I've heard about dinosaurian herbivore defense (generally, it's one of the worst things you can do, as it's both easier to bring the animal down and easier to determine which individuals are weakest within the herd). Though I do think Horner is a lot more guilty of this idea than others. Some of the statements of his about 'herbivores never using antlers or horns for defense and preferentially running away and kicking' are flat out unsubstantiated fantasy.

    Caribou, bison, and elk, it holds true. It's why wolves are far more likely to attack bull elk from behind (when they do choose to attack horned animals--most of the time, partly due to their size, and partly due to their defenses, they opt for those less equipped, which they instead attack towards the front, opting for the throat). I don't mean to dismiss the probability of a primarily sexual basis for those structures (as I said, I agree!), but I do feel that some of the literature dealing with herbivore defense tactics has been too often ignored when speculating on prey defense.

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  3. Tor,

    You are absolutely correct. Horned bovids and cervids often face predators head on and attempt to use their horns/antlers to intimidate (and occasionally do combat) predators. Horns and horn-like structures are likely also used to recognize members of ones own species. It is true that paleontologists, including me, have downplayed some of these roles in the past. Nevertheless, my point is simply that all of this dinosaur headgear probably functioned first and foremost in mate competition, just as it does in extant animals with such extreme structures (e.g., not just deer and antelope, but also chameleons, ants, etc.). Mate competition seems like the best explanation to account for the range of ontogenetic (growth) and phylogenetic (species) variation in these organs, which tend to be highly variable yet species-specific, and develop fully only late in ontogeny. Thanks for the input!

    Scott

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  4. I'd say it's difficult to tell what animals were doing with their headgear (especially without living examples). I'd say it should be taken on a case by case basis. For example, i'd say that Utahceratops is better suited for fighting with each other than Kosmoceratops. Because even seemingly mundane structures could have been used for fighting in unexpected ways. One example is the elephant seal. If it didn't exist today and we had a fossil skull, we would have no idea that they fought by goring each other with their canines. Another example is the red river hog aka bush pig. We wouldn't know the odd protuberances on it's skull actually protected the face when males butted each other. Of coarse these animals are vastly different from ceratopsians. I'm just offering random musings.

    also, i notice that in discussions of Laramidia dinosaurs from the west never get mentioned. There were dinosaurs living on the other side of those mountains in what would become California and Mexico. These include a tyrannosaur (tentatively referred to as Albertosaurus), a giant species of Lambeosaurus (though some think it could be a species of Velafrons), small carnivores, and an ankylosaur (Aletopelta coombsi), to name the more definitive ones. But given their fragmentary nature (Aletopelta is considered the most complete, and it consists of the hip regions with legs, plus a few other bits) it doesn't surprise me that they get overlooked.

    Finally, if what you say is true and these dinosaurs lived in a subtropical swamp environment, then it's doesn't surprise me that so many large herbivores could live there. Swamps are among the most productive ecosystems on earth. If these dinosaurs did have slower metabolisms than similar sized mammals, then the sheer amount of biomass characteristic of swamps could very well have sustained them. again, random musings...

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  5. I remember the "oohs and ahhs" from the crowd at the Cleveland Museum of Natural History when you revealed the two (then unnamed) Ceratopsians in your slide presentation.
    I was wondering if you saw where the Salt Lake Tribune used your discoveries in a political cartoon. Very funny.

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  6. Thanks for the heads up Reed. No I haven't seen the cartoon. Will try to find it.

    accpaleo: Thanks for your comments. You are correct about swamp productivity, and also about the fact that we know very little about dinosaurs from the west coast of Laramidia. Time to make some more discoveries!

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