Friday, October 30, 2009

Toro! Toro! Toro!

Above: Ceratopsian skull specimen AMNH 5116. Triceratops, Torosaurus... or both? Read on...

By now, all dino fans have probably heard the buzz on the indicator: Jack Horner and team are working on a paper which attempts to prove that Torosaurus and Triceratops are the same thing, and that in general, growth series in dinosaurs are often misinterpreted as numerous similar species (something that has long been acknowledged in pterosaurs and recently in early birds like Archaeopteryx and, probably, Confuciusornis).

Here's the quick and dirty background: Triceratops was named by O.C. Marsh in 1889 based on a pair of horns and skull roof collected in 1887 from Colorado. Numerous complete specimens followed, making Triceratops the archetypal horned dinosaur with its two long forward-pointing brow horns and single short, forward-pointing nose horn, in front of a relatively short (by ceratopsian standards), solid frill. The frill is notable: most ceratopsians, including close relatives of Triceratops, have long frills with large openings, or fenestrae, in the bone.

Torosaurus was described a few years later in 1891, also by Marsh, based on two skulls. Unlike Triceratops, the Torosaurus skulls had long frills with the standard fenestrae. Its frill was also smooth around the edges: many Triceratops specimens show that they had small, bony scutes adorning the frill's edge, called epoccipitals.

According to Horner's talks at SVP, which he also summarized in an interview on the podcast The Skeptic's Guide to the Universe (available here), those differences are not due to species variation, or even sexual dimorphism as previously hinted. Rather, Torosaurus is nothing more than the most mature growth stage of Triceratops. The paper isn't out yet so all the data isn't available, but presumably Horner will demonstrate based on microscopic bone growth studies that all the specimens currently assigned to Triceratops are not fully mature, and that like modern birds, some secondary sexual characteristics (such as the expanded, chasm-filled frill) pop up quite suddenly at the 'last minute' in the animal's growth, after it has already reached nearly adult size.
Above: Diagram of a 'classic' Torosaurus skull. By William Diller Matthew, 1915. Public domain.

We can already see heaps of major changes taking place as Triceratops grows. Juveniles have backward curving horns, which completely change to point forward during growth. Remember those epoccipital fringes, the lack of which is so diagnostic of Torosaurus? We already see them becoming reduced from tall, pointed osteoderms in younger forms to smooth and rounded, and finally merging with the frill itself and smoothing out so as to be almost invisible. Indeed, in these oldest individuals, the bone in the center of the frill can also be seen to thin like a man's receding hairline. Given that we already know all of this about Trike's growth, it's not a very huge leap to recognize a long, smooth, holy frill as the next logical step, and those just happen to have been named Torosaurus for 110 years.

The goss has been flying over this online, and a few interesting tidbits have come up. Having grown up in the Northeast US, the most interesting to me concerns the mistaken identity of some specimens of Triceratops. For me, the quintessential Triceratops is the one in the American Museum of Natural History (specimen AMNH 5116). However, as many have pointed out on DinoForum and elsewhere, it's also among the most... well, un-Triceratops like.

Above: Triceratops skull 'classic' vs. specimen AMNH 5116. By Ed T. and Michael Gray (right), licensed.

Compare the images above. On the right is my beloved AMNH Trike. On the left is a 'classic' Triceratops skull. The frill on the AMNH specimen is longer, and lacks epoccipitals. The frill is also tall and back-swept, not flared out to the sides, as in most Triceratops skulls. Not only that, but as you can see in the image at the top of this post (which is a more contrasty view of the same AMNH skull), almost all of the frill has been restored in plaster to conform with what a Trike should look like. There are significant gaps in the middle of the frill entirely filled with plaster... exactly where the fenestrae of Torosaurus go. If Torosaurus and Triceratops are indeed separate species, the AMNH Trike is no Trike at all... it's a Torosaurus in disguise!

Thankfully, it's more than likely that there is no such thing as Torosaurus, any more than there was a Brontosaurus. It's all Triceratops baby, and we can conclude that this famous last of the ceratopsians was indeed last, the only one of its kind in the Lance and Hell Creek Formations that date to the very end of the Mesozoic era.

But... wait... isn't there another named ceratopsian from the same time and place? Named BEFORE Triceratops?? If there was only one Lance/Hell Creek ceratopsian, then Torosaurus get sunk into Triceratops as a synonyms. Does Triceratops then have to be abandoned in favor of... Agathaumas!?
Above: Painting of Agathaumas by Charles R. Knight, 1897. Public domain.
Dun dun duuuuuun!


  1. it is all very interesting stuff...

    we have been prepped for revolations like this from the hell creek before though. the nanotyranus saga has hopefully taught us that looks can be deceiving when it comes to various similar animals in the same formation (in this case the exact SAME formation ;p). normally i don't agree with horner's theories, but these growth series ones of his are sounding pretty convincing to me. especially given the lack of proper young animals of the bigger "species". there really should be some baby t-rexs and pachyelosaurs along side the nanotyranus and stygimolochs to prove they were different coexisting animals...

    though the name Agathaumas is not so catchy, i do love the charles knight painting of it. that has always been one of my favs of his.

    anyways i'm very interested to see how this plays out

  2. This still does not explain material from utah and texas. And how do they explain the greater number of epioccipitals in torosaurus vs. triceratops or the presence of the midline epiparietal that triceratops has and torosaurus does not?

  3. Have to WFTP about the epoccipitals and epiparietal. As for the Texas/Utah material, do you mean the supposed juvenile or sun-adults? AFAIK, the identification of all that material collectively as Torosaurus is based on two skulls, both adult. The referral of juvenile/subadult material to Torosaurus is based on proximity to adult skulls identified as Torosaurus. If adult Torosaurus = adult Triceratops, the problem goes away.

  4. Yes. But they came from a mono-specific bone bed, which typically are of the same species. And these are t. utahensis, not latus, so couldn't t. utahensis still be valid, even if they think latus is not? You can't sink the whole genera with just looking at things found in the north. I think there needs to be a larger sample size before people can make such a brash decision.

  5. Again, I haven't seen the paper, but I understand they're taking the supposed specific/geographic differences into account. WFTP.

    As for the monospecific bonebed... what does that have to do with Horner's hypothesis? He's saying all these things are monospecific, and the differences are due to ontogeny. A monospecific bonebed containing two "Torosaurus" skulls has no bearing on the question either way, since the postcranial material is all even more similar than the skulls anyway.

  6. To be more clear, one thing the paper will (hopefully) address is whether T. utahensis and T. latus are actually different species at all, and if so how these relate to Triceratops prorosus and T. horridus (assuming these are in fact separate species as well, which seems pretty unlikely).

  7. "the nanotyranus saga has hopefully taught us that looks can be deceiving when it comes to various similar animals in the same formation"

    But Nanotyrannus is distinct. No one has ever shown that it is a juvenile T. rex, only hypothesized it was. And it is not.

    BTW, I usually don't buy Horner's theories either, but I think he's right on the money with this Torosaurus = Triceratops thing. The Dracorex = Stigimoloch = Pachycephalosaurus I'm not so sure about - I'm on the fence at the moment.

  8. I think the whole deal with the Pachycephalosaurs is pretty clear, its juvenile, sub-adult and adult, the bone grows that way, good bye Stygimoloch, you were cool. Dracorex, you were used by Bakker as a way to get kids into dinosaurs, so, bye shortlived publicity stunt.

    Nanotyrannus, well, it IS a juvenile, it is not fully grown. Also, the difference is based on, what, BRAIN CASE SHAPE BEING CLOSER TO TARBOSAURUS? Are we even sure that Tarbosaurus is a distinct genus? Better yet, a juvenile, so, 2 species of giant Tyrannosaurines in Hell Creek? Mmmm, I beg to disagree...

    Also, let's see how this ends up, I'm interested. I've also heard this process to be on the verge of happening to plenty of other genus (Lambeosaurus/Corythosaurus/Hypacrosaurus, I'm looking at you.)

  9. Considering the evidences for ontogeny on different pachycephalosaurs "species" are as solid as a rock I can precede the same will happen with the Toro = Trike paper.

    And isn't anyone writing a paper on Nano = T. rex yet?

  10. I have no opinion on the Triceratops vs. Torosaurus issue, but Agathaumas interests me. What I hope to see happen is an explicit comparison to the diagnostic areas in Triceratops, with note of an upcoming ICZN petition if it comes to that (since nobody's going to sink Triceratops). What I unfortunately expect to happen is that they will either not mention it, or else state ceratopsid postcrania are undiagnostic at genus level (which has never been demonstrated, merely assumed) and cite a Dinosauria chapter in support.

  11. Greetings,

    Thom Carr back in 1999 (and subsequently with Tom Williamson in 2004) published his evidence that Nanotyrannus is the juvenile stage for T. rex. While not positively settled (if such a thing were possible), it has by no means been overturned. The decisive evidence has yet to be discovered: either an adult Nanotyrannus which is clearly distinct from Tyrannosaurus rex or a juvenile T. rex of the same ontogenetic stage as Nanotyrannus which is disctinct from Nanotyrannus. Until that time, the hypothesis that Nano is just a baby rex is definitely in play.

    Good catch on the Agathaumus issue. I have the dread sensation of a future in which we consider Manospondylus as the major predator of Agathaumas and Thespesius, the two most common Lancian big herbivores...

  12. But if juvenile T. rex of the same age as the Nano holotype *are* in fact indistingishable from Nanotyrannus, won't this "debate" simply go on forever as long as the Nano, er, "supporters" refuse to accept the most parsimonious position? I assume this is the problem illustrated by Jane, which is either a Nano or a T. rex depending on who you talk to. I guess it'll take a complete growth sequence showing N. lancensis -> T. rex in order to settle it. Unless/unil such a thing is found, I agree the only reasonable thing to do is treat Nano as a juvenile T. rex pending evidence to the contrary.

    Mickey: I also doubt they'll touch Agathaumas, unfortunately, but maybe we'll be pleasantly surprised. Incidentally, is Tyrannosaurus "oficially" a nomen conservandum or did Manospondylus squaeak past the ICZN rule that makes disused 100 year old names automatic nomina oblita?

  13. Manospondylus is supposedly a nomen oblitum so Tyrannosaurus doesn't need a petition. I was wondering if Agathaumas could be a nomen oblitum too, but while it has not been used for 50 years, it has been used as a valid taxon after 1899 (e.g. Hayk 1902; Lull, 1906; Hatcher et al., 1907; Zittel, 1911; Russell, 1930; Romer, 1956). Interestingly, Manospondylus has also been used as a taxon since 1899 in some of those same references. So perhaps it's not really a nomen oblitum.

    As for Nanotrannus vs. Tyrannosaurus, I'm a supporter of synonymy especially since we now have two similar juvenile skulls. People claim the newly discovered braincase differences are too great, but what's our objective metric and just how many theropods have we examined for braincase ontogenetic changes?

  14. I find it funny how everyone puts stock in papers that are not even in print yet, just because they heard someone give a talk about it. If anyone other than Horner had done this they would have been laughed at.

  15. Sounds like the whole aforementioned "Nanotyrannus saga" all over again. ;P One thing I don't understand is why people keep attacking Horner. It seems he lost ALL of his reputation with his theories on T. rex and people forgot that he is one of the great ones alongside Bakker! I mean, this IS his expertise. He DID discover Maiasaura and kin. (The M. peeblesorum adults and nest in the 1970s.)

  16. "remember those epoccipital fringes, the lack of which is so diagnostic of Torosaurus? We already see them becoming reduced from tall, pointed osteoderms in younger forms to smooth and rounded, and finally merging with the frill itself and smoothing out so as to be almost invisible."

    Only if you consider T. prorsus to be a growth stage of T. horridus. Horner is a notorious lumper, and the type of T. prorsus is an old adult, so...

    "Considering the evidences for ontogeny on different pachycephalosaurs "species" are as solid as a rock"

    Says who? You? Who are you?

    "Unless/unil such a thing is found, I agree the only reasonable thing to do is treat Nano as a juvenile T. rex pending evidence to the contrary."

    Uh... There is evidence to the contrary... Read work from people other than Carr and Horner, will ya?

    Oh I give up. If you sholarly acedemic folk want to be wrong, be wrong. Mislead people, disguise fantasy as truth, pretend that things are settled when they are not, sink perfectly valid taxa, continue with that cladistics garbage you LOVE, ruin paleontology for future generations, do whatever the hell you feel like.

    But you can't conceal the truth, no matter how much you wish to.