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The reconstructed skull of Eotriceratops. The actual specimen is not complete, but, based on the recovered elements and the dinosaur’s relationships, we know the dinosaur would have looked similar to Triceratops. Photo by Roland Tanglao, image from Wikipedia.

Triceratops is among the most cherished of dinosaurs. Even that might be a bit of an understatement. Fossil fans threw a conniption when they mistakenly believed that paleontologists were taking the classic “three-horned face” away, after all. But where did the charismatic chasmosaurine come from? Triceratops didn’t simply spring from the earth fully formed–the ceratopsid was the descendant of a long tail of evolutionary forerunners. And in 2007, paleontologist Xiao-chun Wu and collaborators described a 68-million-year-old dinosaur that might represent what one of the close ancestors of Triceratops was like–Eotriceratops.

In 2001, while on an expedition to search the Horseshoe Canyon Formation around the Dry Island Buffalo Jump Provincial Park in Alberta, Canada, Glen Guthrie discovered the partial skeleton of a huge ceratopsid dinosaur. This was the first identifiable dinosaur skeleton found in the top quarter of the formation, and, as Wu and coauthors later argued, the bones represented a new species. They called the animal Eotriceratops xerinsularis.

Paleontological devotees know that “eo” translates to “dawn.” The tiny mammal Eohippus was the “dawn horse” (which Victorian anatomist Thomas Henry Huxley famously characterized for the steed of a tiny “Eohomo“), and there are plenty of dawn dinosaurs such as Eoraptor, Eodromaeus, Eobrontosaurus and Eolambia. The prefix is a kind of honorific, used to indicate the hypothesized beginning of a major lineage or significant change. In the case of Eotriceratops, Wu and colleagues found that the dinosaur was the oldest known member of the evolutionary ceratopsid club containing Triceratops, Torosaurus and Nedoceratops (which, depending on who you ask, may or may not be the same dinosaur).

The individual Guthrie found had fallen apart between death and burial. Aside from some vertebrae, ribs and ossified tendons, the scattered specimen was primarily represented by a dis-articulated skull. When reconstructed, though, the head of Eotriceratops stretched almost ten feet long–about a foot longer than the largest-known Triceratops skull. And while different in some characteristics, Eotriceratops had the same three-horned look of its later relatives Triceratops and Torosaurus.

This isn’t to say that Eotriceratops was directly ancestral to Triceratops, Torosaurus, Nedoceratops or whatever combination of the three paleontologists ultimately settle on. Eotriceratops could be the closest relative of Triceratops to the exclusion of Torosaurus, which would support the idea that those later dinosaurs were separate genera.  Then again, Wu and coauthors pointed out that Eotriceratops might be the most basal member of the subgroup, which would make sense given that it was older than the other three genera. In either case, Eotriceratops can give us a rough idea of the Triceratops and Torosaurus prototype, but we lack the resolution to know if Eotriceratops was ancestral to any later dinosaur. Eotriceratops undoubtedly had some significance in the evolution of the last three-horned dinosaurs, but we need many more fossils to know this little-known dinosaur’s role in the story. Every dinosaur paleontologists find comes with a handful of answers and a myriad of new mysteries.

This post is the latest in the Dinosaur Alphabet series.

Reference:

Wu, X., Brinkman, D., Eberth, D., Braman. 2007. A new ceratopsid dinosaur (Ornithischia) from the uppermost Horseshoe Canyon Formation (upper Maastrichtian), Alberta, Canada. Canadian Journal of Earth Sciences 44: 1243-1265

A sculpture of Torosaurus—or, according to some, a mature Triceratops—outside Yale's Peabody Museum of Natural History. Photo by the author.

I wish I could take dinosaurs away from the media for a while. Someone certainly should. Lazy journalists and unscrupulous documentary creators have amply demonstrated that they just can’t play nice with Tyrannosaurus, Triceratops and kin.

In the past month and a half, we’ve seen aquatic dinosaur nonsense resurface in shoddy news reports, a brief media invasion of hyperintelligent alien dinosaurs and stinky stories about dinosaur farts, not to mention the bizarre creationist/extraterrestrial conspiracy-theory mashup on Ancient Aliens. I’m almost surprised that this glut of utter dreck wasn’t followed by reports of dinosaurs who used their noxious flatulence to propel themselves through space. To paraphrase the immortal words of Ozzy Osbourne, it would seem that dinosaur news has gone off the rails on a crazy train.

And the distortions keep coming. The sci-fi and science news aggregator io9 just drew on a ceratopsid misunderstanding I thought had been left behind two years ago. Yesterday afternoon Ed Grabianowski posted an article titled “Everything you need to know about the scientific controversy that could destroy Triceratops.” The article was meant as a quick survey of recent, and quite controversial, research about whether the horned dinosaurs called Torosaurus and Nedoceratops are really more mature forms of ol’ three-horned face, Triceratops. The general idea is that the solid, rounded frill of Triceratops changed shape and developed two large holes, called parietal fenestrae, relatively late in life, when the dinosaur hit skeletal maturity. What were previously considered to be three different dinosaurs might actually just be three growth stages of the same genus.

Whether this was truly the case is a matter of debate. And while Grabianowski produced a fair review of the research, the post repeated the hyped—and entirely wrong—idea that paleontologists might soon be sinking Triceratops. “If you cried over the sick Triceratops in Jurassic Park, or just loved this horned dinosaur as a kid,” Grabianowski wrote, “there’s one scientific controversy you need to understand right now—it’s the one that may wind up demonstrating that Triceratops never existed.”

Here’s the thing. Triceratops is totally safe. It’s only the dinosaur die-hards who adore Torosaurus and Nedoceratops who have anything to worry about. I covered this two years ago, when the publication of the first paper in this ongoing debate kicked off a wave of ill-informed hysteria. (Although I must say that the Triceratops-Pluto shirt design was pretty cool.)

If—and I emphasize if—Triceratops, Nedoceratops and Torosaurus turn out to be growth stages of a single dinosaur, then the name Triceratops has priority. Paleontologist O.C. Marsh named Triceratops in 1889, and he followed that with the first description of Torosaurus in 1891. Nedoceratops is a newcomer name for a single skull that has been given many monikers over the past century; A.S. Ukrainsky coined the name in 2007. Given the taxonomic arcana that govern the proper scientific names for organisms, Triceratops would remain the proper name for the dinosaur since it was established first.

(“Brontosaurus” was put to bed for the similar reasons. Brontosaurus is a synonym for a dinosaur O.C. Marsh named earlier—Apatosaurus—and paleontologist Elmer Riggs recognized this state of affairs more than a century ago. But Brontosaurus still has a great deal of cultural cachet because museums, books, documentaries, writers and paleontologists keep reminding everyone of the name change. Brontosaurus still lives because we keep reminding people that it didn’t really exist.)

No matter what happens, Triceratops isn’t going anywhere. What we think we know about the dinosaur’s biology might change, but the classic name will stay. I pointed this out on Twitter shortly after the io9 post appeared, and, to io9′s credit, science editor Analee Newitz quickly changed the headline and introduction. I appreciated the speedy edit. The body of the post was a good summary of the argument as it presently stands, but it was painful to see the same “ZOMG, THEY’RE TAKING AWAY TRICERATOPS!” myth used to frame the article.

I’m thrilled that dinosaurs are so popular. Discoveries are coming so fast and furious that it is almost impossible to keep up, and a new wave of cultural dinomania seems to be swelling. That’s why I get so frustrated by misrepresentations of what we’re actually learning about dinosaur lives. We don’t need embellishment—whether it’s teasing us with the false threat of a beloved dinosaur’s disappearance or the idea that sauropods farted themselves into extinction. The wonderful resolution we’re gaining into dinosaur biology and evolution is best communicated simply, directly, and without having to find some snarky or inaccurately comedic hook that ends up distorting what we actually know. And I would be remiss if I didn’t point out that scientists sometimes play this game, too. Chemist Ronald Breslow tried to use armchair speculation of space dinosaurs to give an otherwise mundane paper a little spice—a ham-fisted and ill-executed grab for attention that I sadly saw some other writers agree with. There’s no such thing as bad publicity, right?

Of course, I realize that simply shaking my fist in the air and frustratedly growling “Do better!” isn’t going to fix the problem. There are seemingly innumerable internet news outlets, and never enough professional science writers, so it’s all too easy for dumbed-down churnalism and other misconstrued reports to richochet around the web. Maybe we’ve seen the last of dinosaur farts and space tyrannosaurs, at least for a while, but places like the Daily Mail, FOX News, and the various outlets that pass off barely modified press releases as news will undoubtedly come up with another headache-inducing hook in the not-too-distant future. If it’s not too much to ask, though, I’d like it if the usual suspects gave it a rest. Dinosaurs are amazing enough without the sensationalism.

Another year, another fantastic spate of dinosaur discoveries. Even as 2011 draws to a close, the findings keep rolling in—from the way Deinonychus used its killer cutlery to the first record of sauropod dinosaurs from Antarctica and sexual selection among dinosaurs. There has been such a glut of interesting papers that it would be impossible to mention every bit of dinosauriana from this year, but here is a partial listing of some of the stories that caught my eye.

Dinosaur Growth

Everyone knows that there are lots of unknown dinosaur species left to be discovered. What has become increasingly contentious is the question of how many species can be counted among what has already been collected. This year saw a continuation of the 2010 “Toroceratops” debate with a paper on the enigmatic Nedoceratops by Andrew Farke early in the year, followed by a response to his paper by John Scannella and Jack Horner this month. Likewise, paleontologists suggested that the hadrosaur Anatotitan and the tyrannosaur Raptorex were really just growth stages of other known dinosaurs (the latter being similar to Tarbosaurus, a juvenile of which was also described this year).

Dinosaur senses

How did dinosaurs perceive their world? Two significant papers approached this question—one focused on smell (see the video above), and the other vision. As with studies of dinosaur growth, though, investigations of dinosaur senses can be controversial. Last week’s issue of Science included a comment and reply about the idea that the bony rings preserved in the eyes of some dinosaurs might be used to reconstruct the time of day when the animals were most active.

Archaeopteryx

This year marked the 150th anniversary of the discovery of Archaeopteryx. But 2011 has been full of ups and downs for the Urvogel. Even though an 11th specimen of the feathered dinosaur was announced, a controversial paper proposed that the creature was not an early bird but rather a non-avian dinosaur more distantly related to the first birds. Exactly what Archaeopteryx is and what that interpretation means for our understanding of bird evolution will continue to be debated.

New species

New dinosaurs are named just about every week, but two in particular caught my eye: Brontomerus, a sauropod whose name translates to “thunder thighs,” and Teratophoneus, a short-snouted tyrannosaur. (I just realized that both were found in Utah, though, so perhaps I have a bias for my adoptive state!)

That is just a smattering of findings from 2011. Shout out your favorite 2011 dinosaur discoveries in the comments. And, if you want to see how 2011 compares to previous years, see my lists from 2010 and 2009.

A comparison of Triceratops (left) and Nedoceratops (right). From Scannella and Horner, 2011.

When the “Toroceratops” controversy broke in the summer of last year, I felt sorry for Nedoceratops. Hardly anyone said a word about this unusual horned dinosaur. Fans of Triceratops wept, wailed, and gnashed their teeth at their misapprehension that Museum of the Rockies paleontologists John Scannella and Jack Horner had exterminated the beloved horned dinosaur while paleontologists wondered if this dinosaurian mainstay of the Late Cretaceous could have grown into what had previously been called Torosaurus. But no one shed a tear at the proposition that Nedoceratops, too, might have been just a growth stage of Triceratops.

Known from a solitary skull on display at Smithsonian’s National Museum of Natural History, Nedoceratops has perplexed paleontologists since it was first described more than 100 years ago. The skull was found from the same end-Cretaceous strata that yielded Triceratops and Torosaurus, yet the dinosaur eventually labeled Nedoceratops was different from both. The skull had the general Triceratops-Torosaurus shape, but was distinguished by the lack of a nasal horn, a small opening in the preserved parietal portion of the frill, and two asymmetrical holes in the wing-shaped squamosal bones which made up the border of the frill. (These holes were thought to be old battle scars from some Cretaceous clash, but later studies showed these unusual perforations to be natural parts of the animal’s bone growth.) Scannella and Horner disagreed. Some of the unusual features, such as the apparent absence of a nasal horn, fell within the expected variation of Triceratops, and they interpreted the small hole in the parietal to be an early stage of the larger, rounded openings seen in the elongated frills of Torosaurus. Therefore, Scannella and Horner proposed, the Nedoceratops skull was a dinosaur virtually caught in the act of transitioning between the traditional Triceratops and Torosaurus forms, linking all three animals together into a single, late-life growth series.

Andrew Farke, a ceratopsian expert at the Raymond M. Alf Museum of Paleontology, came to a different conclusion when he published a reanalysis of the Nedoceratops skull earlier this year. The mix of features exhibited by Nedoceratops distinguished the dinosaur from both Triceratops and Torosaurus, Farke argued, which would remove the form with transitional features from the growth series. More than that, Farke offered up additional criticisms of the growth series Scannella and Horner proposed—Torosaurus might not be sunk, after all.

Now Scannella and Horner have published a response to Farke’s response. To an outsider, this might look like an echo of the 19th century “Bone Wars,” when the cantankerous naturalists Edward Drinker Cope and Othniel Charles Marsh battled each other in print over the proper identification and interpretation of dinosaurian remains. The headline for LiveScience’s report on the new paper states that the “debate rages,” though the argument is probably better cast of a difference of opinion that has generated some friendly competition. Farke and Scannella are close colleagues, and as Farke mentioned in a behind-the-scenes post on his Nedoceratops work, the paleontologists have helped critique and strengthen each other’s arguments prior to publication. The paleontologists are not about to assault each other at the next Society of Vertebrate Paleontology meeting, either.

Despite the collegiality between the parties, however, Scannella and Horner object to Farke’s critique. For one thing, the Montana-based researchers argue, each of the seemingly unique features of Nedoceratops can be found within the variation of Triceratops (which they count as including Torosaurus-type animals). Though Triceratops is classically portrayed as being a “three-horned face,” when I asked about the apparently absent horn of Nedoceratops, Scannella pointed out that “there are many Triceratops specimens which show similar low, subtle nasal ornamentation—not quite to the degree seen in ‘Nedoceratops’ but certainly approaching that state.” Alternatively, the nasal horn of Nedoceratops might have been broken off or lost after death since the horn does not actually fuse to the nasal bones until late in life. At the moment no one knows for sure whether the horn was lost or was simply never there, but Scannella emphasizes that none of these scenarios hinders the idea that Nedoceratops might be better categorized as a Triceratops.

And that’s not all. Some of the features thought to mark the Nedoceratops skull as an old individual that had finished growing are ambiguous, Scannella and Horner say. The rough bone texture and fusion between certain skull bones—thought to be indicators of maturity, and even old age—are variable in Triceratops and don’t necessarily represent the age range of the animal accurately. They uphold their original interpretation of the dinosaur as a Triceratops, and I have to admit that I was amused that Scannella and Horner pointed out that Nedoceratops translates to “insufficient horned face” in their paper. Though this refers to the apparent lack of a nasal horn, there is a certain poetic justice to it in a paper which seeks to sink the name. “I think ‘insufficient horned face’ is a very appropriate name given that the genus likely represents variation within Triceratops,” Scannella said.

Scannella and Horner offer an explanation for the slit-like opening on one side of the specimen’s frill. (The completed Nedoceratops skull on display was partially reconstructed, so we don’t know for sure if there was a matching hole on the other half.) The projected sequence of transformation from Triceratops to a Torosaurus-type form predicts that there would be a stage in which the solid frill of Triceratops would develop depressions or holes that would eventually open to create large, circular fenestrae. Scannella explains the transformation happening like this:

As Triceratops matured, the parietal developed increasingly thin areas which eventually formed the holes previously thought to be characteristic of “Torosaurus.” If you take a typical Triceratops with a thick, solid frill and have it undergo this transformation to “Torosaurus,” there’s going to come a point where the parietal is going to begin to develop openings. These openings will likely start off rather small and continue to grow as resorption continues and the parietal expands. This is what we see in “Nedoceratops“—it’s a fairly mature specimen, the squamosals are slightly elongate (approaching the morphology observed in “Torosaurus“), and the parietal has a small opening in the same place where in Triceratops we see thinning occurring and in “Torosaurus” we see holes. So—one possibility is that this is a distinct genus of dinosaur that has tiny holes in its parietal. Another is that this is simply a Triceratops caught in the act of becoming “Torosaurus.” Jack and I favor the hypothesis that “Nedoceratops” is actually a transitional morphology, between Triceratops and “Torosaurus.”

One of the areas of debate has been the number of triangular, bony ornaments called epiossifications around the border of the Triceratops frill, which is composed of the parietal and squamosal bones. Previous studies have established that these bones start off being prominent, pointed ornaments, but as Triceratops aged these bones flattened out until they were barely visible. The question is whether the number of some of these epiossifications could change during growth, thus bridging the gap between the different number of these ornaments on the parietals of Triceratops and Torosaurus.

While Triceratops typically has five or six of these bones, called epiparietals, Torosaurus have been found with spots for 10 to 12, requiring the number to double if Scannella and Horner are right. This kind of addition has not been seen in well-sampled populations of horned dinosaurs before, but Scannella and Horner propose that such changes were indeed possible. As evidence, they cite a single epiossification marked by two peaks, which they hypothesize is an ornament in the process of splitting into two. Additional specimens will be needed to determine whether this double-peaked adornment truly was splitting during a transformative growth stage or is an unusual and unique variant. While Farke cautions that he hasn’t seen the specimen in question himself, he does offer an alternative interpretation. The double-peak shape “could also just be resorption of the tip without splitting a single element into two,” he says. “This is relatively common in ceratopsids—many of them tend to resorb the tips of the ‘high points’ on the skull, and that may be what is happening here.” If this is the case, then the epiossification would be part of the typical transformation into flatter adornments and not indicative of splitting.

This aspect of debate brings up the question of how useful epiossification counts might be for identifying distinct ceratopsids in the Hell Creek Formation. Individual variation, changes in growth and possibly even variation from one slice of time to the next might complicate matters. “As we are finding more and more Triceratops in the Hell Creek Formation of Montana,” Scannella says, “we are seeing specimens with quite a bit of variation in both the number and position of frill epiossifications–a finding which urges caution before considering epiossification number and position a set in stone indicator of taxonomic identity, at least in taxa closely related to Triceratops.” Farke takes a different view. “[Scannella and Horner are] almost certainly correct that there is stratigraphic variation in epiossification count (presumably related to evolutionary change in a lineage),” he says, but points out that “This would strengthen the argument that epiossification count has phylogenetic significance … [I]f early Torosaurus have one count and late Torosaurus have another count, this would suggest that this trait changes through time and we can use epiossification count to distinguish different species.” Though all this argument over ceratopsid ornaments might seem esoteric, it is a key part of the discussion over what Nedoceratops and Torosaurus truly were. Did some ceratopsid dinosaurs add—and even double— frill ornaments as they matured? The answer to that question will have a major influence on the future of this debate.

What was Nedoceratops? That still depends on who you ask, and there is more than one possible answer. Farke, while noting that “Scannella and Horner raise some valid critiques of my diagnosis of Nedoceratops” in the new paper, still doesn’t see the dinosaur as an intermediate growth stage. “[W]e do still disagree on the taxonomic relevance of things like the parietal fenestrae,” Farke says. “[T]hey cite [the fenestrae] as transitional morphology between the Triceratops-morph and the Torosaurus morph of a single animal’s growth trajectory, whereas I would posit it as the end-member morphology for whatever Nedoceratops is.” And these aren’t the only options. “Of course, Nedoceratops might be an unusual or pathological individual of Triceratops. I’m not particularly married to any hypothesis at this point,” Farke says.

If Nedoceratops is an intermediate growth stage between the classic Triceratops and Torosaurus body types, further sampling of the Hell Creek and Lance Formations should eventually turn up still-growing Triceratops with similar features. Then again, if Nedoceratops is a distinct genus we would expect to eventually find juvenile individuals which share specific features with the single known skull to the exclusion of Triceratops and Torosaurus. Or maybe Nedoceratops is just a weirdo Triceratops.

This isn’t just a bit of paleontological arcana. The scientific conversation about Triceratops growth emphasizes the difficulties of recognizing prehistoric species and understanding their biology. What were once considered to be different species may just be growth stages or variants of one dinosaur, and these revisions affect our understanding of dinosaur evolution, biology, and ecology. I asked Scannella for his thoughts on the implications for his hypotheses, particularly given the fact that many dinosaurs are known from single, and often partial, specimens:

Increasingly, we are learning that many skeletal features in a wide variety of dinosaurs change throughout development.  There is also individual variation to consider. If all the differences between specimens are considered taxonomically informative, then it is easy to see how 16 species of Triceratops were named based on small differences in cranial morphology. Dinosaurs changed as they grew—and so, we need to evaluate which features are the most taxonomically informative. This can be hard to do if there is only one specimen of a particular dinosaur. We can start by examining developmental trends in dinosaurs thought to be closely related to that one specimen – as we’ve done with “Nedoceratops.” Examination of the bone microstructure is also important, in order to get an idea of relative maturity.

Paleontologists have recognized the problems of identifying slightly different specimens as new species before, but the debate over Triceratops—as well as Tyrannosaurus, Pachycephalosaurus, and other Hell Creek dinosaurs—has helped reinvigorate interest in how little dinosaurs grew up. Paleontologists are still in the relatively early phases of this investigation, and there are far more questions than there are definitive answers. The clues that will resolve the question of whether Triceratops was the lone ceratopsid of the Hell Creek still wait in museum collections and the expansive fossil graveyard that is the badlands.

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

Scannella, J., & Horner, J. (2011). ‘Nedoceratops’: An Example of a Transitional Morphology PLoS ONE, 6 (12) DOI: 10.1371/journal.pone.0028705

A drawing of the skull of Nedoceratops (left) and a restoration of the dinosaur's head (right). From Lull, 1905.

What is Nedoceratops? That depends on who you ask. The single known skull could represent a transitional growth stage between Triceratops and Torosaurus head shapes in a single species of dinosaur, or it might be a unique species of horned dinosaur that lived alongside its better-known relatives.

The suggestion that Nedoceratops was truly a Triceratops caught in the act of rearranging its skull has sparked a renewed interest in this dinosaur. Though known to paleontologists for over a century, the dinosaur was often viewed as an oddball and did not even receive a full redescription until about a month and a half ago. Nedoceratops has never been as popular or well-known as its relatives Triceratops and Torosaurus, and so I was surprised to learn that a life restoration had once been made of this peculiar creature.

A paper on the restoration accompanied a 1905 scientific description published by Richard Swann Lull but mostly written by John Bell Hatcher. This was not a bit of scientific claim-jumping. Hatcher had been working towards completing a massive monograph on horned dinosaurs. It had been started by his former boss, O.C. Marsh, who died of typhus before he could finish the book. The task of wrapping it all up went to Lull, who decided to publish Hatcher’s description of the Nedoceratops skull separately in 1905. (At the time, Lull proposed that the dinosaur should be called Diceratops, though the name has been changed multiple times.)

Lull’s restoration was of a battered animal. Unlike other horned dinosaurs, Nedoceratops had two unequally-shaped holes in the squamosal bones on the sides of its frill. Hatcher thought these might be natural holes in the skull, but Lull argued that, since Triceratops, Torosaurus and Nedoceratops undoubtedly used their horns and frills like spears and shields, “It seems vastly more probable that [the squamosal holes] are ‘old dints of deep wounds’ received in combat.” The animal survived the presumed injury, and Lull thought some kind of “horny or leathery integument” would cover the gaps in the frill.

We now know that Lull was probably wrong. When I asked paleontologist Andy Farke—who redescribed the skull—what he thought about the strange skull holes of Nedoceratops, he replied:

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.

Even so, Lull’s restoration is remarkable. I cannot recall seeing any other model or sculpture of Nedoceratops, and it is a rare vision this contentious dinosaur in the flesh.

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

Lull, R.S. (1905). Restoration of the horned dinosaur Diceratops. American Journal of Science, 4 (4), 420-422