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The skull of Nedoceratops in oblique view, snout-view, and a line drawing (with grey areas denoting where the skull was reconstructed). From Farke, 2011.

What is Nedoceratops hatcheri? That depends on whom you ask.

For over 120 years the problematic skull of this horned dinosaur has been bounced around the literature under different names and attributions. While it was originally described as a distinct genus, Diceratops, some paleontologists later lumped it under Triceratops, at least until recent work raised the possibility that it really was a unique dinosaur. Then there was the problem of what to call it. The dinosaur’s original name was occupied by a wasp, and two different publications proposed two different replacement names, with Nedoceratops just beating out the proposed name Diceratus.

Then came last year’s controversial paper hypothesizing that the dinosaur Torosaurus was truly the adult stage of Triceratops. In this growth series, Museum of the Rockies paleontologists John Scannella and Jack Horner proposed, Nedoceratops represented a transitional stage between the young adult (Triceratops) and old adult (Torosaurus) stages, meaning that Nedoceratops should really be called Triceratops, too. But ceratopsian expert Andy Farke of the Raymond M. Alf Museum of Paleontology disagrees. In a recently-published PLoS One paper, Farke at long last gave Nedoceratops a detailed description and found that it stands apart from other horned dinosaurs.

Determining the identity of Nedoceratops is important for figuring out how many kinds of horned dinosaurs there were at the end of the Cretaceous, as well as testing ideas about the growth of Triceratops. The trouble was that very little had actually been written about this dinosaur. “[N]obody had ever published a full scientific description of the [Nedoceratops] skull,” Farke explained via e-mail, “so it was an opportunity ripe for the taking.”

What makes Nedoceratops unique—and has made it so frustrating to assign—is a mosaic of features on its skull. This dinosaur lacks a nasal horn, has brow horns that stick up almost vertically, and slot-like openings in its frill. The only known Nedoceratops skull also has uneven openings on its squamosal bones that make up the sides of its frill which have puzzled scientists for years.

“[N]obody has been able to decide if these features are just the results of injury, abnormality, individual variation, or genuine differences between species,” Farke says, but he makes a compelling case that the first three traits might be indications that Nedoceratops was unique. They do not seem to overlap with known specimens of Triceratops or Torosaurus. The openings in the squamosal bones are another matter. As interpreted by Farke:

The old thought was that these holes were the result of accidental “gorings” during horn-to-horn combat between rival dinosaurs. But, Darren Tanke and I recently noted that most aspects of the fenestrae argue against them being the result of injury. Instead, we think they were probably just the result of bone resorption in an area of the frill that was already thin to begin with. No horn thrusts required.

Additionally, the texture of the bone and the degree of fusion between the parts of the skull appear to indicate that this Nedoceratops skull represents an old individual.  This makes it unlikely that it represents a transitional growth stage of Triceratops.

If Nedoceratops isn’t really a pathological or young adult Triceratops, what does this mean for the still-debated “Toroceratops” hypothesis? Well, for one thing, the proposed Triceratops-Torosaurus continuum would lose its intermediate stage. More than that, though, Farke points out that the degree of changes required to turn a Triceratops skull into a Torosaurus skull are unknown in any other horned dinosaur, particularly the addition of bony knobs around the edge of the frill (epiossifications) and the opening of holes in the frill’s parietal bones late in life. If these modifications actually occurred, Triceratops had an extremely unusual growth series. And, the icing on the cake, Farke mentions that a juvenile Torosaurus may have been hiding in plain sight for decades in a specimen called YPM 1831. Provided that further study confirms this identification, it would support the idea that Triceratops, Torosaurus and Nedoceratops truly were different dinosaurs.

The existence of three different horned dinosaurs in western North America at the same time would be important to investigations about the ecology and evolutionary history of the dinosaurs just before the mass extinction that wiped them out. Asked whether this indicates that dinosaurs were still going strong at the end of the Cretaceous or already dwindling, Farke replied:

I would suggest that dinosaurs were still going strong, but of course our view is very skewed towards western North America (where these horned dinosaurs lived). We know next to nothing about what was going on with dinosaurs elsewhere in the world at that time! Even within North America, many important dinosaur specimens from the end of the Mesozoic (including that of Nedoceratops) weren’t collected with full geological data. Better field protocols are changing this (especially through ongoing work at Museum of the Rockies), but we have a long way to go yet.

Not everyone is going to agree with the new paper’s conclusions, of course, but Farke is not exactly locking horns with his colleagues about this. There were no rumbles at the annual Society of Vertebrate Paleontology meeting last October, and as Farke documented on his own blog, the new Nedoceratops paper was actually improved through conversations with Scannella and Horner.

That is not to say that these scientists agree, though. When asked about whether Nedoceratops should be separated from Triceratops, Scannella replied:

The hypothesis that the single specimen of ‘Nedoceratops‘ represents a distinct genus of horned dinosaur is based on noting how it differs from other specimens. If you’re looking for differences between specimens, they’re easy to find—but differences can’t tell us anything about relationships; only similarities can do that. No evidence was presented which indicates ‘Nedoceratops‘ was more mature than any other young adult Triceratops and its tiny parietal fenestra is what you would expect if it was in the process of developing large ‘Torosaurus‘ fenestrae.

Furthermore, there may be additional evidence that Nedoceratops really does fall within the range of variation seen among Triceratops. Over the past decade the Museum of the Rockies has excavated multiple Triceratops specimens from the famous Hell Creek Formation, providing paleontologists with a way to determine just how much individuals varied from one other. According to Scannella, “There are numerous Triceratops specimens that overlap in anatomical traits with ‘Nedoceratops,’” although these specimens have yet to be fully described.

I also asked Scannella about one other related point. When the public controversy over the Toroceratops hypothesis blew up last year, many critics on the Internet stated that Triceratops was larger than Torosaurus, and therefore the Torosaurus specimens could not be adult forms of Triceratops. I asked Scannella to respond to this point:

I am a lot taller than my Dad, but that doesn’t make me older. When you have a huge sample size, like we now do for Triceratops, it is possible to see just how much variation is present. One of the things that varies is size. There are young Triceratops which are very large and there are more mature ones that are quite small. The sources of this variation may include things like ontogenetic variation, stratigraphic variation, sexual variation, and individual variation—so there is a lot to take into account.

The debate over the fate of Nedoceratops and Torosaurus is not over. Not by a long shot. No single paper is going to make all the difference here. Each academic article is another part of an ongoing discussion about how to identify dinosaur species and the implications those rearrangements might have. Being that Farke’s paper is one of the first—but surely not one of the last—replies in this debate, I’ll give him the last word:

Undoubtedly, many other paleontologists will have something to say about these issues. Some will agree, some will disagree, some will show parts of my paper are incorrect, and others will present more supporting data (at least I hope, on all counts). I suspect the next few years will feature much, much more discussion on these fascinating horned dinosaurs!

(Farke has also chronicled the process of writing the Nedoceratops paper in a three-part series at The Open Source Paleontologist: Part I, Part II, Part III.)

References:

Farke, A. (2011). Anatomy and Taxonomic Status of the Chasmosaurine Ceratopsid Nedoceratops hatcheri from the Upper Cretaceous Lance Formation of Wyoming, U.S.A PLoS ONE, 6 (1) DOI: 10.1371/journal.pone.0016196

Scannella, J., & Horner, J. (2010). Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny Journal of Vertebrate Paleontology, 30 (4), 1157-1168 DOI: 10.1080/02724634.2010.483632

A line drawing of the Teratophoneus skull (a) and the skull of Albertosaurus for comparison (b). From Carr et al., 2011.

It missed the 2010 Utah dinosaur rush by nearly a month, but a new tyrannosaur from the southern part of the beehive state makes up for its tardiness by helping to fill a gap in the famous group’s evolutionary history.

Almost one year ago, paleontologists Thomas Carr and Thomas Williamson described Bistahieversor sealeyi, a tyrannosaur from New Mexico and the first representative of this group to be described from the American Southwest. Now, in the journal Naturwissenschaften, Carr and Williamson join colleagues Brooks Britt and Ken Stadtman in describing a second southwestern tyrannosaur. They have named it Teratophoneus curriei, and  it was a different sort of predator from its larger, northern cousins.

Found in the 75-million-year-old rock of Utah’s Grand Staircase-Escalante National Monument, Teratophoneus is known from a partial skull and additional elements from the rest of the skeleton. Its head was short—a departure from the typically long-snouted profiles of other tyrannosaurs—and it was a close relative of the northern forms Daspletosaurus and Tyrannosaurus. Based on its anatomy and its geographic place, Teratophoneus appears to be part of a unique radiation of southern tyrannosaurs.

Paleontologists have seen this pattern before. Just last year scientists described two new horned dinosaurs from the same place—Utahceratops and Kosmoceratops—which indicated that dinosaurs in the American Southwest evolved differently from their cousins to the north. There must have been some sort of barrier that kept dinosaur populations separate and caused the northern and southern groups to evolve in distinct ways. The peculiar anatomy of Teratophoneus adds further support to this idea.

Given its name—Teratophoneus roughly translates as “monstrous murderer”—you might think that this predator was a terrifying giant, but the new tyrannosaur was not quite as imposing as the famous Tyrannosaurus. Although it was a bit larger than the long-snouted genus Alioramus from Asia, Teratophoneus is estimated to have weighed about three quarters of a ton—about one tenth the mass of an adult Tyrannosaurus. (As the authors note, though, this first Teratophoneus specimen was a subadult, so they did grow a little bigger.) Just what it preyed on is as yet unclear, but hadrosaurs and horned dinosaurs have already been described from the same rock formations. Juveniles of these herbivores, at least, would have almost certainly been on the menu.

And Teratophoneus was not the only tyrannosaur found within the fossil-rich Grand Staircase-Escalante National Monument. During the 70th annual Society of Vertebrate Paleontology meeting, Utah Museum of Natural History scientist Mark Loewen introduced attendees to an older and even stranger tyrannosaur found there. This creature has yet to be fully described, but, along with Teratophoneus and Bistahieversor, it is one of the many specimens that is rapidly altering what we thought we knew about the evolution of the tyrant dinosaurs.

References:

Carr, T., Williamson, T., Britt, B., & Stadtman, K. (2011). Evidence for high taxonomic and morphologic tyrannosauroid diversity in the Late Cretaceous (Late Campanian) of the American Southwest and a new short-skulled tyrannosaurid from the Kaiparowits formation of Utah Naturwissenschaften DOI: 10.1007/s00114-011-0762-7

Interpretive Dance: Everything Dinosaur recounts an unusual class project that is curiously reminiscent of many off-off-Broadway productions: “The children…(aged 5-6) put on a dancing display as they interpreted how they thought the dinosaurs met their demise…. at first they pretended to be different types of dinosaurs….As the music grew louder….the ‘dinosaurs’ became scared and started running around in a panic.  At the crescendo of the music, the asteroid hit the Earth and all the children fell down and stayed very still, indicating the demise of the Dinosauria.”

And, Speaking of Mass Extinction: The Dinosaur Fossil Blog presents this video (in Danish, above) showcasing a cake that recreates the asteroid impact that is believed to have wiped out the dinosaurs. The paleo-baker also “found room to add an erupting volcano that represents the alternative theory – that the ashes and gasses from a giant eruption was the actual cause of the extinction.”

The Top Ten Dinosaurs That Could Eat Han Solo: I’m glad that’s finally settled.

Yes, But Can They Eat Han Solo? At Bob’s Dinosaur Blog, the Top Ten Dinosaurs By Continent.

Size Matters: At SV-POW!, Matt Wedel presents this excellent tutorial on how to determine the mass of a dinosaur.

Artistic Statement: At Flying Trilobite, Glendon Mellow contemplates why science often inspires visual art, but visual art rarely inspires science: “I criticized the idea underlying a symposium discussing ‘Art as a Way of Knowing.’  I said that art is more a Way of Exploring. It doesn’t provide new knowledge, only creates new, imaginative, metaphorical links between areas of knowledge.”

An Albertosaurus scares off a smaller predatory dinosaur in this Royal Tyrrell Museum diorama. Large tyrannosaurs would have competed with smaller carnivores for carcasses to scavenge. Image from Flickr user mcwetboy.

Was Tyrannosaurus rex a fearsome hunter or a scavenger? The answer is “both.”

In the early 1990s, the paleontologist Jack Horner popularized the idea that Tyrannosaurus fed entirely on carrion. The idea that this dinosaur—the “prize fighter of antiquity“—could not catch or kill other dinosaurs was shocking. Reporters and documentary-makers ate it up, but other paleontologists were quick to respond with evidence that Tyrannosaurus truly was the apex predator of its time. The academic debate over whether Tyrannosaurus was capable of bringing down live prey has been over for years now, and a study published today in the Proceedings of the Royal Society B finds new support for Tyrannosaurus as one of prehistory’s super-predators.

In order for Tyrannosaurus to have made a living as an obligate scavenger, tons of dinosaur carcasses would have to have been scattered over the Cretaceous landscape. If there were enough dead dinosaurs, Tyrannosaurus could have hypothetically gotten by through scavenging, but the trouble is that it was not the only carnivore around. Smaller, more numerous carnivores would have seriously limited its feeding opportunities.

As tabulated by paleontologists Chris Carbone, Samuel Turvey and Jon Bielby in their new study, there were as many as nine other species of meat-eating dinosaurs alongside Tyrannosaurus during the Late Cretaceous of North America. They ranged in size from the large tyrannosaur Albertosaurus down to the six-foot-long “raptor” Dromaeosaurus. (The authors count the supposed “pygmy tyrant” Nanotyrannus on their list, but these specimens are probably juvenile Tyrannosaurus and do not belong to a distinct genus.) Altogether, there was an entire guild of meat-eating dinosaurs that would have competed for carcasses, just as we see mammals of different sizes competing for carcasses on the African savanna today. In order to subsist on carcasses alone, adult Tyrannosaurus would have been in intense competition with multiple, smaller predators, including their own offspring.

A graph showing the relative abundance of carnivores (blue) and herbivores (red) in the ecosystems where Tyrannosaurus rex lived. From Carbon et al., 2011.

After compiling a list of carnivorous species and prey species, Carbone and colleagues used information about the ecology of modern ecosystems to estimate the number of available carcasses on the landscape and the ability of the carnivores to detect them. The carcasses of small herbivorous dinosaurs would have been relatively abundant, but an adult Tyrannosaurus would have had to walk for days to reach a large carcass. In fact, the researchers estimate that an individual Tyrannosaurus would have had to search for nearly a year before finding a five-ton carcass, and it would have had to rely upon more frequent and less-filling meals.

Unfortunately for Tyrannosaurus, more abundant carnivorous dinosaurs probably would have arrived at the carcasses first. Many small mouths can destroy a body faster than one big one. For example, let’s say that a Triceratops weighing about 8,500 kilograms keels over and dies. Based upon the estimates of search time and carnivore abundance used in the new study, about 1,000 Dromaeosaurus-level carnivores could have reached the carcass in the same amount of time that it would take one Tyrannosaurus to find it. There were simply more of them spread over the landscape.

Overall, the best bet for a scavenging Tyrannosaurus would be to find smaller carcasses more frequently, but even these were probably consumed before it could reach them. As the authors of the new study state, “it is extremely unlikely that an adult T. rex could use scavenging as a long-term sustainable foraging strategy.”

Tyrannosaurus was the biggest meat-eating dinosaur within its ecosystem and certainly would have dominated any carcass it came across, but the likelihood of it reaching a carcass before its destruction at the jaws of smaller, faster dinosaurs was low. We know from fossil evidence that Tyrannosaurus cannibalized carcasses of its own species, and that its cousin Tarbosaurus wasn’t above scavenging, but in order to survive the tyrant king had to hunt. That it did so is clear from its anatomy—Tyrannosaurus was well-adapted for delivering devastating bites that would have felled the large herbivorous dinosaurs of its time. The hunting method of this dinosaur, how often it had to hunt, whether it hunted in groups, and other questions remain, but there can be no doubt that Tyrannosaurus was a formidable predator.

References:

Carbone, C., Turvey, S., & Bielby, J. (2011). Intra-guild competition and its implications for one of the biggest terrestrial predators, Tyrannosaurus rex Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2010.2497

A reconstruction of the skeleton of Linhenykus. The lighter (white) elements represent what was actually discovered. From Xu et al., 2011.

When it was first described in 1993, Mononykus was one of the strangest dinosaurs known. It had the slender, light build of some of the “ostrich mimic” dinosaurs, yet it possessed two stubby, one-clawed hands and a few other subtle characteristics that placed it in a new group called the alvarezsaurs. Since that time, multiple species of alvarezsaur have been found, and the latest discovery has just been announced in the journal PNAS.

Named Linhenykus monodactylus, the new dinosaur is known from a partial skeleton found in the 84- to 75-million-year-old fossil deposits of Inner Mongolia. It was not a very large dinosaur—as Dave Hone commented at Archosaur Musings, “the living animal would probably have been able to s[t]and comfortably in the palm of your hand”—but what makes it stand out are its heavily built forearms.

Like many of its close relatives, Linhenykus had only one functional finger—a single, stout digit tipped with a heavy-duty claw. Where Linhenykus differs, however, is that it lacked any additional fingers. Other alvarezsaurs discovered so far had tiny, vestigial fingers that were still retained alongside the primary finger. Even in Mononykus, where only the functional finger has been found, there were small indentations in the bone of the hand which suggest that it also had two additional, tiny fingers. Not so in Linhenykus. There is a small, second bone of the palm of the hand next to the large finger, and since this small bit of bone could not have supported a finger we can say that Linhenykus is the first one-fingered dinosaur known.

Curiously, however, the loss of the additional fingers in Linhenykus was not the culmination of a long-term evolutionary trend among the alvarezsaurs. When compared to other members of this group, Linhenykus fell out closer to the base of the family tree than species which retained the vestigial fingers. This means that the anatomy of Linhenykus represents a pattern of mosaic evolution: It retained a suite of archaic characteristics seen among early members of the group, but it also had peculiar specializations not seen among later species such as Mononykus. The loss of the vestigial fingers in Linhenykus was a specialization not yet seen among any other alvarezsaurs.

Further discoveries and future analyses will flesh out the evolutionary pattern seen among these dinosaurs, but one of the recurring questions is why alvarezsaurs had such unique forelimbs. How did they evolve, and what were they used for? These are two distinct questions—even if we can determine the function of a particular trait, that does not necessarily explain how that trait evolved in the first place.

At the moment, the favored hypothesis is that Mononykus, Linhenykus and their relatives used their claws for digging into ant and termite nests. As pointed out by Phil Senter in a 2005 Paleobiology study, the forelimbs of Mononykus were modified so that the palms of their hands faced downward and they were capable of scratch digging with their functional fingers. No one had yet found a preserved termite or ant nest that was raided by an alvarezsaur, but, given the similarity of their claws to those of modern anteaters and pangolins, the idea that these dinosaurs feasted on insect colonies remains the most popular explanation for their unique anatomy.

References:

Xu, X., Sullivan, C., Pittman, M., Choiniere, J., Hone, D., Upchurch, P., Tan, Q., Xiao, D., Tan, L., & Han, F. (2011). A monodactyl nonavian dinosaur and the complex evolution of the alvarezsauroid hand Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1011052108

Senter, P. (2005). Function in the stunted forelimbs of Mononykus olecranus (Theropoda), a dinosaurian anteater Paleobiology, 31 (3), 373-381 DOI: 10.1666/0094-8373(2005)031[0373:FITSFO]2.0.CO;2