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A metallic Triceratops, photographed on the grounds of a Minneapolis mansion. Photo by Mark Ryan.

I never would have thought of Minnesota as a hot spot for dinosaurs, but reader Mark Ryan keeps sending in sightings from the Gopher State. His latest submission is of one of several metallic dinosaurs that once graced the lawn of a mansion in uptown Minneapolis. The question is, what dinosaur was it? It clearly had the elongated frill and brow horns of what has previously been called Torosaurus, but the solid frill is a dead giveaway for Triceratops. Given the new debate over whether “Torosaurus” is really just an adult Triceratops, perhaps this sculpture can be seen as a sort of transitional growth phase, though—since it was built many years ago and has recently disappeared from the lawn—I wouldn’t bet on it.

Have you stumbled across a dinosaur in an unexpected place? If you have, and have a photo of the encounter, send it to us via dinosaursightings@gmail.com!

Skeletal restorations of Utahceratops (left) and Kosmoceratops (right). The yellow bones are those that have been recovered for each species. From Sampson et al., 2010.

At the height of the golden era of dinosaur science, it takes something special for a newly described dinosaur species to stand out. Dinosaurs with dual sickle claws, humps,  or unexpected bristles more readily grab the attention of the public than more familiar-looking forms, but looks aren’t everything. A pair of horned dinosaurs described today in PLoS One are noteworthy for reasons that go beyond their strange appearances.

A few months ago, I was fortunate enough to visit the Utah Museum of Natural History’s paleontology field crew at their camp in southern Utah’s Grand Staircase-Escalante National Monument. The arid, rocky landscape was rich in dinosaur fossils, but 75 million years ago this same place would have looked very different. During that time in earth’s history, near the close of the Cretaceous, a shallow sea over the center of North America divided the landmass into two separate continents: Appalachia to the east and Laramidia to the west. The area which is today Grand Staircase-Escalante National Monument was in the middle of the thin western continent, and according to Scott Sampson, University of Utah paleontologist and lead author of the new paper, the place was “a wet, swampy setting akin to present-day northern Louisiana.” Crocodiles, turtles, and at least 16 unique species of dinosaurs thrived here, including the two horned dinosaurs announced today.

Named Utahceratops gettyi and Kosmoceratops richardsoni, respectively, the two dinosaurs belonged to a subdivision of the horned dinosaur family called chasmosaurines. Roughly speaking, this group of horned dinosaurs can often be identified by their large brow horns and their wide, squared-off frills, and both Utahceratops and Kosmoceratops fit the classic chasmosaurine type. Nevertheless, both were distinct from species previously recognized and were significantly different from each other. While Utahceratops had relatively short brow horns in front of a large frill that was slightly indented inwards along its top margin, the slightly smaller Kosmoceratops had longer brown horns and an array of spikes that spilled forwards over its frill like a chasmosaurine comb-over.

In contrast to more familiar chasmosaurines like Triceratops, though, the browhorns in both Utahceratops and Kosmoceratops were oriented out to the side rather than forward. Why this should be so is unclear. Co-author Andrew Farke of the Raymond M. Alf Museum of Paleontology says, “it’s hard to know for sure, but in modern horned animals horn orientation usually relates to horn function.” Perhaps Utahceratops and Kosmoceratops had similar styles of combat with members of their own species, Farke hypothesizes, or maybe the peculiarity was inherited in both from a common ancestor. Likewise, according to Sampson, the sideways orientation of these horns is also seen in another horned dinosaur from Coahuila, Mexico, and may be a common characteristic of chasmosaurines from this part of Laramidia. Among these dinosaurs, “the sideways-oriented horns offer another means to lock heads and engage in contests of dominance,” Sampson says; “they would also have made effective visual signals, particularly in Kosmoceratops.”

Utahceratops and Kosmoceratops were also very different from the horned dinosaurs that lived in the same area a few million years earlier. While both of the new dinosaurs came from the Kaiparowits Formation, horned dinosaurs of a different sort have been found in the national monument’s 80-million-year-old Wahweap Formation. These older dinosaurs, such as the many-horned Diabloceratops, belonged to another branch of the horned dinosaur family tree called the centrosaurines. “If you were to line up the skulls [of the Wahweap and Kaiparowits dinosaurs] side by side,” Farke says, “they would look strikingly different!” especially since the two newly described dinosaurs had relatively larger and more ornamented frills.

Given the degree of completeness of both dinosaurs (entire skulls for both, the majority of the skeleton of Utahceratops, and the skeleton except the tail, feet, and forelimbs in Kosmoceratops), their description is a major contribution to our understanding of ceratopsid anatomy and diversity. What makes them especially noteworthy, however, is that they confirm the existence of disparate pockets of dinosaur evolution along the western continent of Laramidia. These genera were not evenly spread from Mexico to Canada, but were distinct from the horned dinosaurs that lived at the same time in the northern part of the continent. This is not just an accident of sampling, the authors of the new study propose, but a signal of a real biogeographical phenomenon.

The picture that emerges from the distribution of the horned dinosaurs around 75 million years ago is that there were at least two separate centers of chasmosaurine evolution on the western continent. Where there were Chasmosaurus, the recently-described Mojoceratops and Vagaceratops (previously Chasmosaurus irvinensis, but renamed by the authors of this study) to the north, Utahceratops, Kosmoceratops and Pentaceratops lived in the far south. Based on the distribution of these dinosaurs in space and time, Sampson, Farke and their colleagues propose that about 77 million years ago there was a barrier that separated chasmosaurines in the north from those in the south. This barrier would have precipitated the divergent evolution of the northern and southern groups identified in the study, though the close relationship of Kosmoceratops and Vagaceratops found by the scientists suggests that these dinosaurs shared a close common ancestor that spread after this impediment was removed about 75.7 million years ago. As Sampson states by e-mail, the recognition of this patten raises some important questions about dinosaur evolution on Laramidia:

The implications of this finding huge, given that Laramidia was a landmass about one-third the size of present day North America, and much of this area was likely off limits to large dinosaurs because of large mountain ranges to the west.  Today we have a handful of rhino-to-elephant sized mammals living on Africa.  At present, it seems that there were at least 15-20 rhino-to-elephant sized animals living on Laramidia 76 million years ago, despite the fact that it was less than one-fifth the size of Africa.  How did so many species of giants co-exist on such a small chunk of land?  The answer may relate to available fodder (more biomass than at present) and/or to metabolic rates (slower in dinosaurs than in mammals).  Either way, these finding suggest that the hothouse world of dinosaurs was, at least in some respects, very different than the one we know today.

Furthermore, if the pattern of evolution in these horned dinosaurs really was influenced by the existence of an ancient barrier, then the same signs of isolation should be seen among other dinosaurs, as well. Hadrosaurs and tyrannosaurs probably would have been isolated in the same way, and the discovery and description of additional dinosaurs from Grand Staircase-Escalante National Monument will be pivotal in further tests of this idea. Determining just what the barrier might have been, though, is another mystery. At present there is no sign of an actual physical barrier, though the authors of the new study suggest a previously-unidentified mountain range, temporary flooding by the nearby sea, a turbulent river system, or some kind of ecological barrier as possibilities.

The story of Laramidia will not be resolved by one paper alone, but will take years of study by many paleontologists. This is a good thing. Through something as simple as the description of two dinosaurs, paleontologists have placed the fauna of an entire lost continent in a new context, and, armed with a new set of questions, paleontologists can return to the strata of southern Utah in search of answers.

References:

Sampson, S., Loewen, M., Farke, A., Roberts, E., Forster, C., Smith, J., & Titus, A. (2010). New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism PLoS ONE, 5 (9) DOI: 10.1371/journal.pone.0012292

If paleontologists have said it once, they have said it a hundred times: non-avian dinosaurs and humans never coexisted. Most people who insist otherwise are creationist cranks who believe that evidence of a living dinosaur would somehow undermine evolutionary theory, but I understand that Hollywood has to play by different rules. Dinosaurs are just not as exciting without people to menace, and so it has been traditional to use time travel, the existence of prehistoric “lost worlds,” fertilized eggs preserved for over 65 million years and genetic engineering experiments gone awry to bring dinosaurs and people together. But none of these options worked for the creators of the 1970 Hammer film When Dinosaurs Ruled the Earth. They wanted dinosaurs and other prehistoric monsters to attack scantily-clad cavepeople, and so they made a film that a biblical fundamentalist could take as a documentary rather than fiction.

When Dinosaurs Ruled the Earth doesn’t begin with a shot of a steaming, primeval forest, but of a gaggle of tanned and oiled cavepeople who have crawled out of their cliffside dwellings to engage in their regular “let’s pick which blond woman we want to sacrifice” ritual. Naturally, the prospective victims are not very happy about this—one throws herself off a cliff—but when they try to escape they are hindered by the fact that they are wearing prehistoric underwear so skimpy that it actually makes it more difficult for them to run away. It would have made more sense for them to lose the push-up bras and just bolt for it, though I imagine going streaking during prehistory would have presented its own unique risks.

In any event, one of the Cenozoic supermodels—named Sanna—does manage to escape by jumping into the sea and is promptly rescued by a conveniently placed group of fishermen whose unfortunate garments remind us why it’s never wise to wear thongs in a windstorm (I wish I were talking about sandals here—yikes). It is among this group of unfortunately attired men that we meet Tara, our film’s scruffy male lead. Meanwhile, back at the ranch, the musclebound leader of the cavepeople is clearly upset that the sacrifice did not go as planned; he shouts incomprehensible phrases and gestures widely to get people to go do whatever it is they do. Maybe this was intended as a bit of fun for the audience—make up your own dialogue as you go along—especially since words like “akita” appear to mean: “Over there”; “Stop”; “Give me that”; “Come over here” and “Let’s have pancakes for dinner tonight.”

For me, though, the film’s real stars are the prehistoric creatures that help to thin out the cast, and the audience’s first look at one of the film’s exquisite stop-motion monsters comes when the fishermen return with the woman to their camp. While the dudes were out fishing, someone brought a plesiosaur (which is, of course, not a dinosaur) to the big clam bake, but damned if they knew what to do with the thing. It was too angry to just stick an apple in its mouth and start slow-roasting it, and when half the village runs over to examine their new visitor their dinner tries to make a break for it. Unfortunately, though, the plesiosaur wanders right into a mess of fluid the tribe uses for lighting fires, and soon the only question on anyone’s mind is: “White meat or dark?”

Things don’t look so rosy the next day. The cliffdwellers are still miffed that their sacrifice just up and left, and Tara’s wife isn’t too happy that he came back with a new, blond girlfriend. When Sanna’s captors show up, she makes a break for it, and thanks to an assist from an angry Chasmosaurus she gets a little extra time to get away. That does little to help the fisherman and his friends, though—when they set out after her the same dinosaur causes them a spot of trouble before throwing itself into what sounds like a bottomless pit (lots of roaring, but no crash). Sanna also encounters some of the dangerous local fauna when she finds herself being enveloped by a carnivorous plant, although I would not recommend her escape technique of reaching outside to stab inwards at the plant’s tough outer hide (pointsy towardsies = bad).

The remainder of the film is little more than an excuse to watch Victoria Vetri run around in an embarrassingly small bikini. Thankfully, there are a few more prehistoric critters to help break the movie’s naked tedium. A newly-hatched baby something-o-saurus and its mother (which look like cousins of the Beast from 20,000 Fathoms) provide a brief bit of comic relief as they try to figure out whether Sanna is friend or food; an attack by an oversized Rhamphorhynchus livens things up a bit, and when Tara returns home to find that his tribe doesn’t think it’s cool that he ran off with someone else’s sacrifice, they try to serve him up on a raft to the local Tylosaurus. (The marine reptile responds by tossing him off the raft. “Yecch! Human? No thanks – I’m trying to cut back on junk food.”) Given how good these stop-motion creatures look, though, it is sad that the film also resorts to gluing plates and spikes on alligators and monitor lizards and making them fight, a practice that is despicable as it is lazy.

In the end, a giant tidal wave wipes away the coastal village but delivers our heroes to a mountaintop to observe a lunar eclipse. Dumb, but attractive, they would go on to found a settlement along the southern coast of California which would eventually be named Los Angeles. What happened to all the prehistoric monsters is unclear, though. Perhaps they got so tired of the cavepeople’s shenanigans that they eventually died of boredom—a risk I certainly felt while watching this vintage 1970s schlock.

The reconstructed skeleton of the Tyrannosaurus rex specimen known as "Black Beauty". From Wikimedia Commons.

Tyrannosaurus rex was an obligatory inclusion in every book and documentary about dinosaurs I saw as a kid. It was the tyrant king of all dinosaurs, the supreme predator of the end-Cretaceous, but for all its majesty no one could explain where it had come from. Along with its kin—such as Albertosaurus and Tarbosaurus—Tyrannosaurus simply seemed to be the culmination of a trend towards larger size and ferocity among predatory dinosaurs, but plotting the succession of giant theropods during the course of the Mesozoic did not seem to provide many clues about the origins of the tyrannosaurs.

As summarized in a new Science review by a team of tyrannosaur experts, however, new discoveries made in the last decade have finally placed Tyrannosaurus in its proper evolutionary context. In the past year alone, no less than six new tyrannosauroids have been either discovered or identified from previously-known specimens, and this growing knowledge of tyrannosaur evolution has confirmed that the largest predators of Late Cretaceous North America started off small. The first tyrannosaurs were not derived from already-large Jurassic predators such as Allosaurus, but instead were relatively small coelurosaurs, with small heads and long arms, which evolved during the Middle Jurassic more than 165 million years ago. Proceratosaurus, a crested dinosaur from England once believed to be closely related to Ceratosaurus and other early theropods, was just recently found to be one of the first tyrannosauroids. At a glance, Proceratosaurus and similar tyrannosaurs would have looked more like “raptors” than like their more famous relatives. Exceptionally-preserved specimens of the Early Cretaceous tyrannosauroid Dilong from China show that, like their relatives among the coelurosauria, these dinosaurs were covered in feathery dino-fuzz.

After almost a century of uncertainty, it was finally confirmed that enormous Late Cretaceous tyrannosaurs evolved from small, elaborately-ornamented coelurosaurian ancestors. The approximately 80 million years between the first tyrannosaurs and the radiation of truly giant forms is still relatively sparsely known, though. The recent discovery of the long-snouted genus Xiongguanlong and the announcement of the miniature tyrant Raptorex have illustrated that there was no single, slow evolutionary march towards the Tyrannosaurus rex body form. Instead there was a radiation of relatively small genera which preceded the development of large body size, and there are probably a number of strange Late Jurassic and Early Cretaceous tyrannosaurs waiting to be found.

There is more to recent tyrannosaur research than just filling out evolutionary trees, though. Not only is Tyrannosaurus rex the most famous of all dinosaurs, but thanks to numerous specimens and decades of scientific study it is also the most extensively studied. Bite forces, brain anatomy, running speed, growth rates, bone microanatomy, biogeography and other aspects of its paleobiology have all been—and continue to be—extensively investigated. The abundant remains of some of its close relatives, such as Albertosaurus, have even allowed paleontologists to see how different the last tyrannosaurs were; paleontologists could hardly wish for better fossilized records of these dinosaurs. Research will continue, and new discoveries will continue to revise our understanding of tyrannosaur evolution, but it is wonderful that a more complete history of the tyrannosaurs is beginning to come together.

References:

Brusatte SL, Norell MA, Carr TD, Erickson GM, Hutchinson JR, Balanoff AM, Bever GS, Choiniere JN, Makovicky PJ, & Xu X (2010). Tyrannosaur Paleobiology: New Research on Ancient Exemplar Organisms. Science (New York, N.Y.), 329 (5998), 1481-1485 PMID: 20847260

A reconstruction of Hesperosaurus on display at the Museum of Ancient Life at Thanksgiving Point, Utah.

Measuring diversity in the fossil record can be a tricky task. Short of inventing time travel, there will be always be some uncertainty about how many species of dinosaur existed at any one place and time, and as we learn more about the fossil record it may turn out that what we once thought to be distinct species or genera really belonged to already-known taxa (or vice versa). Stegosaurs are not immune from such lumping and splitting, and in his contribution to the stegosaur issue of the Swiss Journal of Geosciences, paleontologist Ken Carpenter used the debate over Hesperosaurus to dig into what distinguished this armored dinosaur from Stegosaurus.

Earlier this week I wrote about a new study describing skin impressions and other soft-tissue traces of the stegosaur Hesperosaurus mjosi. What I did not mention was that some paleontologists have proposed that this dinosaur was actually a smaller species of the more famous Stegosaurus genus, which would make its name Stegosaurus mjosi. Carpenter, who was one of the scientists who named Hesperosaurus in 2001, disputes this, but notes that whether the contentious stegosaur falls into one group or the other relies on more than anatomy alone.

Back in the Bone Wars era, when Stegosaurus was first described, paleontological rivals E.D. Cope and O.C. Marsh were in uncharted territory as far as taxonomy was concerned. The bits and pieces of the fossil animals they found had not been seen before, so it is not surprising that they created a vast accumulation of names to label them all (to say nothing of the competition between them that likely influenced their scientific practices). Given what we know now, though, any paleontologist who applied a new name to every bone scrap they found would be derided by the paleontological community. The naming of a new species—or the synonymy of two old ones—must be explained in minute detail, but even then different scientists have different perspectives on how different two fossils have to be in order to be designated as two different species.

That different species of dinosaur actually existed is immediately obvious. Tyrannosaurus rex and Stegosaurus stenops were so different from each other that it is at once apparent that they were two distinct species of dinosaur. Where a scientist’s personal views come into play are cases where there are two groups of animals which are only slightly different from each other. Do these two groups represent different growth stages of the same animal, different populations of the same species, different species of the same genus, or well-distinguished genera which can readily be told apart? Since, as Carpenter notes, dinosaur taxonomy is based on the comparison of bones alone, disputes can easily arise over how much variation a species had and what falls outside that range.

As for Hesperosaurus, the debate over its validity has been greatly influenced by the material O.C. Marsh used to create the name Stegosaurus armatus in 1877. The fossils were very scrappy, and compared to skeletons discovered since the 19th century, are not very useful in distinguishing these bones from other better-established Stegosaurus species such as S. stenops and S. ungulatus. This means that almost any restoration of the first species Marsh described, Stegosaurus armatus, is going to be a composite of other specimens and therefore obscure the defining characteristics of Stegosaurus as seen in the other species. As a result, it would be possible to lump almost any dinosaur with characteristics similar to the sparse materials Marsh found into the genus Stegosaurus, and it was on that basis that Hesperosaurus was proposed to be a unique species of Stegosaurus.

As Carpenter (and, in the same volume, Peter Galton) argues, however, Stegosaurus armatus is not the best dinosaur to use for determining differences between Stegosaurus species. If the more complete Stegosaurus stenops is taken as representative of the genus, it clearly differs in enough characteristics from Hesperosaurus for both to be considered separate genera. In fact, the differences between them have only become more apparent since more complete specimens of Hesperosaurus have become known.

Overall, I think Carpenter makes a solid case for Hesperosaurus; when compared to the better-known species of Stegosaurus, it was clearly a very different animal. Nevertheless, the fact that two groups of animals were easily distinguishable from each other does not tell us whether we should group them as different species or genera. That is something that is proposed, debated and revised according to the ideas of scientists, and there is no doubt that paleontologists will continue to play the dinosaur name game as research continues.

References:

Carpenter, K. (2010). Species concept in North American stegosaurs Swiss Journal of Geosciences, 103 (2), 155-162 DOI: 10.1007/s00015-010-0020-6