A month in dinosaurs (and pterosaurs): 3, Minotaurasaurus and giant chasmosaurines


More musings on dinosaury things from January 2009. For the back-story you'll need to see part 1 and part 2, both of which are on theropods (and, specifically, on maniraptorans). This time we look at ornithischians...

One ornithischian in particular has been the subject of much discussion lately. Namely, the Upper Cretaceous Mongolian ankylosaurid
Minotaurasaurus ramachandrani Miles & Miles, 2009. This isn't such an inappropriate name - after all, the holotype specimen does have bull-like horns that project outwards from above its eyes - but it doesn't sound very euphonious... and shouldn't it be Minotaurosaurus anyway? The skull of Minotaurasaurus is pretty neat-looking: it has a broad, squared-off beak, is covered on its dorsal surface by pyramidal osteoderms, sports large horns on the cheeks and rear corners of the skull, and has a series of unusual openings in the nasal region (Miles & Miles 2009) [the drawing above is by Waylon Rowley].


That's all very nice, but there's actually nothing new here if you already know ankylosaurs: Minotaurasaurus is similar to another Upper Cretaceous Mongolian ankylosaurid, Pinacosaurus, specifically to P. mephistocephalus Godefroit et al., 1999 [shown here]. Both share those weird accessory openings in the nasal region, among other things (nobody really knows what these were for, but it's been suggested that they housed glands or erectile tissue). The only real difference between Minotaurasaurus and Pinacosaurus is that the former has that broad, squared-off premaxillary beak whereas Pinacosaurus has far narrower premaxillae (Godefroit et al. 1999, Hill et al. 2003). Minotaurasaurus is also extremely similar to another Mongolian ankylosaurid: Saichania chulsanensis. The two are said to differ in the orientation of the pterygoid, orbit shape and other details. The precise relationship between Minotaurasaurus and/or Pinacosaurus and Saichania needs, I think, some evaluation, but it's surprising that Miles & Miles (2009) didn't even cite Godefroit et al.'s (1999) paper on P. mephistocephalus*.

* Incidentally, I once went to a meeting where a poster announced the discovery of P. mephistocephalus. The amusing thing is that a cladogram included only P. mephistocephalus, a salmon, a lungfish and a cow. This is one of those in-jokes again.

It's not just the phylogenetic affinities of Minotaurasaurus that have been the subject of discussion, but also the provenance and origin of the specimen. Miles & Miles (2009) stated that the specimen was purchased by V. S. Ramachandran (hence the specific name), and we now know that it was, more specifically, purchased at a fossil show. And like lots of specimens sold at fossil shows, it may not have been obtained legally (Dalton 2009). On the one hand, a lack of provenance data and absence of legal documentation doesn't automatically make a specimen scientifically worthless. On the other hand, gone are the days when it was ok to get fossils out of countries without the appropriate permission. We wait and see what will happen in the case of Minotaurasaurus.

Incidentally, for those of you wondering whether I'll get round to doing another Ankylosaur Week this year, I have to say it's looking doubtful.

New news on giant chasmosaurines


Moving now to marginocephalians, ceratopsians have been in the news lately. For starters we have Farke et al.'s (2009) paper on combat in Triceratops. In recent decades it has become increasingly recognised (mostly thanks to comparison with extant horned tetrapods) that the frills and horns of horned dinosaurs predominantly functioned intraspecifically, either in combat or in display. Given the irresistible idea that these dinosaurs grappled with one another over mates or territory or resources or whatever, there has been some interest in testing the possibility of intraspecific combat [adjacent image, from Farke et al. (2009), shows incident rate of cranial lesions on the various skull bones of Triceratops and Centrosaurus].

But how do you test for this in long-dead animals? One possibility is to use models - as in, actual, plastic little dinosaur models - and see how the horns and frills match up when posed in possible combat positions. This is what Farke (2004) did: he concluded that, if Triceratops did fight by locking horns, then injuries on certain regions of the frill, jugal and horncore tip should be present in the fossils. Farke et al. (2009) represents the next logical step in research: the authors looked for, found, and analysed preserved lesions on Triceratops skulls. The lesions in Triceratops were mostly concentrated in the regions where they were previously predicted to be most abundant: their presence in these regions of the skull was statistically significant, ergo the hypothesis that the horns were used as weapons in intraspecific combat is supported (Farke et al. 2009).

The authors also looked at the skull lesions of a ceratopsid that lacked long brow horns (the centrosaurine Centrosaurus). In this taxon, the incidence of lesions was much lower, and those lesions that were present were not concentrated on the frill or cheek region. These data provide further support for the idea that horned dinosaurs with long brow horns fought and injured each other intraspecifically with those horns. In contrast, the forms lacking long brow horns might have mostly relied on display, or may have fought by stabbing or butting the body rather than the head. The latter possibility is in fact supported by the fact that fractured ribs are known for these dinosaurs. Finally on this subject, you'll know already that Andy Farke has his own excellent blog - The Open Source Paleontologist - and here, of course, he discusses this research further.


Also on the subject of giant chasmosaurine ceratopsids, something else we've been discussing a lot this month has been the 'new' name for the chasmosaurine ceratopsid Diceratops hatcheri. Diceratops was first named by Richard Swan Lull in 1905 (this was in John Bell Hatcher's monograph: Hatcher died of typhus before completing the work). Its status as a valid genus has been somewhat controversial: we'll get to that in a minute. Anyway, it was pointed out by Mateus (2008) that Diceratops was preoccupied by an ichneumon named in 1869. The chasmosaurine therefore needed a new name, so Mateus published Diceratus. It now turns out that Ukrainsky (2007) had already done all of this: Ukrainsky's name is (in my opinion) rather poorer than Mateus's but, regardless, it has priority and is therefore the one we have to use. It's Nedoceratops. 'Nedo', Ukrainsky explained, indicates 'insufficiency', though quite why Nedoceratops is insufficient was never explained. Maybe its lacks of a prominent nasal horn makes it 'less sufficient' than Triceratops.

While Nedoceratops is undoubtedly similar to Triceratops, the only known specimen is different enough from its better known relative (and from the other member of the 'giant chasmosaurine' clade, Torosaurus) for at least some horned dinosaur workers to regard it as a distinct taxon. Compared to Triceratops, it has been said to be shorter-faced, and it has more erect brow horns and a rounded stump in place of a nasal horn. It also differs in having a thin parietal with small fenestrae, and in having squamosal fenestrae. In their paper on Eotriceratops, a fourth member of the 'giant chasmosaurine' clade, Wu et al. (2008) regarded all of these genera as distinct, and they further found Nedoceratops and Torosaurus to form a clade.


However, Hunt & Lehman (2008) regarded Nedoceratops as synonymous with Triceratops (as have a few previous authors). Furthermore, I learnt recently (thanks to peer-review) that some marginocephalian workers think that Eotriceratops is of questionable status, and that the characters regarded by Wu et al. (2008) as diagnostic for Eotriceratops are instead merely the consequences of ontogenetic variation within Triceratops. These characters include the shape of the epijugal (the horn-like element that projects sideways from the cheek) and the form of the epoccipitals (the small bones that line the edges of the frill). If Eotriceratops does fall within the range of variation (ontogenetic or otherwise) of Triceratops, what does this mean for Nedoceratops and Torosaurus? I realise that ontogenetic and intra-populational variation might mean that at least some alleged dinosaur taxa aren't 'taxa' at all (Aublysodon, Stygivenator, Nanotyrannus and Dinotyrannus come to mind), but in this case I am - for the time being - inclined to regard all four 'giant chasmosaurines' as distinct [Hunt & Lehman's (2008) Torosaurus reconstruction is shown here. Like other Lehmanesque ceratopsids, note that it's shown with a freaky-short tail. And, incidentally, many of you will know the aforementioned Hunt as ReBecca Hunt-Foster of Dinochick Blogs].

That'll have to do for now on the ornithischians, though I also wanted to discuss Holliday & Witmer's (2008) very neat paper on cranial kinesis in dinosaurs. These authors argue that claims of alleged cranial kinesis in non-avian dinosaurs - such as the maxillary pleurokinesis proposed for iguanodontians and the alleged facial and palatal kinesis reported for some non-avian theropods - don't stand up to scrutiny, and they show that non-avian dinosaur skulls actually lack the requisite details that might have permitted kinesis. The good news (for me) is that you don't need me to discuss this research here: Andy Farke provides a good discuss of it here at The Open Source Paleontologist, and a ton of information (and the paper itself) is available here at Casey Holliday's webpage.

Well, so long Ornithischia (for now). What next?

Refs - -

Dalton, R. 2009. Paper sparks fossil fury. Nature doi:10.1038/news.2009.60

Farke, A. A. 2004. Horn use in Triceratops (Dinosauria: Ceratopsidae): testing behavioral hypotheses using scale models. Palaeontologia Electronica 7 (1): 10p.

- ., Wolff, E. D. S. & Tanke, D. H. 2009. Evidence of combat in Triceratops. PLoS ONE 4(1): e4252. doi: 10.1371/journal.pone.0004252

Godefroit, P., Pereda Suberbiola, X., Li, H. & Dong, Z.-M. 1999. A new species of the ankylosaurid dinosaur Pinacosaurus from the Late Cretaceous of Inner Mongolia (P.R. China). Bulletin de L'Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre 69-Supp. B, 17-36.

Hill, R. V., Witmer, L. M. & Norell, M. A. 2003. A new specimen of Pinacosaurus grangeri (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia: ontogeny and phylogeny of ankylosaurs. American Museum Novitates 3395, 1-29.

Holliday, C. M. & Witmer, L. M. 2008. Cranial kinesis in dinosaurs: intracranial joints, protractor muscles, and their significance for cranial evolution and function in diapsids. Journal of Vertebrate Paleontology 28, 1073-1088.

Hunt, R. K. & Lehman, T. M. 2008. Attributes of the ceratopsian dinosaur Torosaurus, and new material from the Javelina Formation (Maastrichtian) of Texas. Journal of Paleontology 82, 1127-1138.

Mateus, O. 2008. Two ornithischian dinosaurs renamed: Microceratops Bohlin 1953 and Diceratops Lull 1905. Journal of Paleontology 82, 423.

Miles, C. A. & Miles, C. J. 2009. Skull of Minotaurasaurus ramachandrani, a new Cretaceous ankylosaur from the Gobi Desert. Current Science 96, 65-70.

Ukrainsky, A. S. 2007. A new replacement name for Diceratops Lull, 1905 (Reptilia: Ornithischia: Ceratopsidae). Zoosystematica Rossica 16, 292.

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

More like this

and shouldn't it be Minotaurosaurus anyway?

Of course. Except that the ICZN doesn't care (anymore).

BTW, I got the in-joke. :-) :-) :-)

By David MarjanoviÄ (not verified) on 16 Feb 2009 #permalink

Apparently the Minotaur had an undocumented mate.

And, for consistency, shouldn't that have been Nedorogatoglaz, Miciceratops, or Tap[e]inoceratops?

"and shouldn't it be Minotaurosaurus anyway?"

Shhh...don't mention that. Hopefully if the taxon gets sent back to China and renamed, we can still use Minotaurosaurus for something else (though it does fit the ankylosaur).

Nedoceratops...yeah, it is a rather...poor...name. For a menagerie of reasons. Not to mention that according to Dinochick, the paper renaming Diceratops that Ukrainsky claims he wrote has been unable to be found.

On the subject of Nanotyrannus and such, that's a discussion for another day, and a hornet's nest that doesn't need to be stirred up.

Plastic dinosaur models...I knew I picked the right field to go into. I would also think that chasmosaurines bashed horns more likely than centrosaurines, on the basis that numerous chasmosaurines had solid frills (i.e. Triceratops), and centrosaurines had large holes in their frills.

By Metalraptor (not verified) on 16 Feb 2009 #permalink

Metalraptor: the Nedoceratops paper is indeed findable, and I have a copy (as does ReBecca). Thanks to the kind soul who pdf-ed it for us, I won't mention his name in case he is swamped with requests.

If short-tailed ceratopsids are recognizably "Lehmanesque," does that mean everyone is just guessing at how long their tails were?

By Brad McFeeters (not verified) on 16 Feb 2009 #permalink

"Metalraptor: the Nedoceratops paper is indeed findable, and I have a copy (as does ReBecca). Thanks to the kind soul who pdf-ed it for us, I won't mention his name in case he is swamped with requests."

Okily Dokily. But the name still stinks.

By Metalraptor (not verified) on 16 Feb 2009 #permalink

I asked Dr. Ukrainsky in an email what he meant by "Nedo" and this was his response: "Russian prefix "nedo" (insufficiency sensu lato) means, that this ceratopsian has lack: nasal horn absent."

Thanks for the review Darren. :)

"Not quite [Tri]ceratops".

By David MarjanoviÄ (not verified) on 16 Feb 2009 #permalink

Incidentally, I once went to a meeting where a poster announced the discovery of P. mephistocephalus. The amusing thing is that a cladogram included only P. mephistocephalus, a salmon, a lungfish and a cow. This is one of those in-jokes again.

That's nothing; at one SVP someone had a poster with a cladogram that included broccoli as the outgroup (complete with skeletal reconstruction, which in the case of broccoli is just a silhouette).

Sheesh, I don't like the name Nedoceratops even more than I didn't like Diceratus! I'm going to keep calling it Diceratops, thankyouverymuch. As to ceratopsian tail-lengths, Lehman's recent Pentaceratops paper also suggests a very short tail for that chasmosaurine, and in fact Lehman considers the five-horned face's body to be "stumpy" by comparison to other chasmosaurines like Triceratops, which I thought was great.

In the same paper, Lehman discusses ontogenetic and sexual morphs in ceratopsids, and convincingly argues that most ceratopsids were probably monospecific, and differences in cranial ornamentation are the result of ontogeny, sex, or both. And after all the papers I've been reading about centrosaurine ontogenetic growth, I'm sold. Just look at what Pachyrhinosaurus or Einiosaurus went through. And then there was that paper not so long ago by Horner and...somebody...detailing the ontogenetic changes in the skull of Triceratops.

Now, there are some obvious exceptions. Centrosaurus apertus is different from C. brinkmani, and Pachyrhinosaurus canadensis is separate from P. lakustai. But I do think it's interesting that Michael Ryan (and others) have suggested that C. apertus is the female of Styracosaurus canadensis! To sum up: ceratopsids are AWESOME.

Zach Miller: Yes indeed. Ceratopsids have always been my favourite group of dinosaurs.

Oh, and you actually mean Styracosaurus albertensis, right? I find such a hypothesis quite unplausible, especially when Centrosaurus apertus is stratigraphically lower than Styracosaurus albertensis, IIRC.

"Incidentally, I once went to a meeting where a poster announced the discovery of P. mephistocephalus. The amusing thing is that a cladogram included only P. mephistocephalus, a salmon, a lungfish and a cow. This is one of those in-jokes again."

I suppose eventually someone is going to come up with a joke that goes as follows "An ankylosaur, a lungfish, a cow, and a salmon walk into a bar..."

By Metalraptor (not verified) on 16 Feb 2009 #permalink

We have complete tails for Pentaceratops and Anchiceratops, and they're indeed VERY short; the almost complete tail of Chasmosaurus suggest a short tail too. What is wrong in the reconstruction is the angle of the posteriormost sacrals and the cranial caudals, which are strongly downturned in ceratopsids, not straight like basal coronosaurs. Dodson suggested that Centrosaurus apertus was a female of Styracosaurus, but this is very unlikely giving the monospecific bonebeds known for both taxa, the temporal segregation within the Dinosaur Park Fm, and the secondary sexual characters of adult Centrosaurus. Although some feature of Eotrice are possibly ontogenetic-related, the epijugal shape, the very deep triangular narial process of the pmx and the fossa on the rostroventral surface of the frill are distint from other maastrichtian chasmosaurines...

By Lukas Panzarin (not verified) on 16 Feb 2009 #permalink

In the matter of horned Dinosaurs, it's nice to have research confirm the likelyhood of combat taking place between individuals. While there's been much debate over whether they used their horns on predators or each other, the two things aren't mutually exclusive.

By Raymond Minton (not verified) on 16 Feb 2009 #permalink

There was a poster two years ago at SVP in Austin titled "Dinosaurian Mass Turbation..."

By the way, 'mephistocephalus' is the coolest species name ever. EVER. (!)

It doesn't seem too similar to Pinacosaurus mephistocephalus, despite the similarities in the horns, especially due to the vaulting of the skull in that taxon, and the large, flatened ornamention of the cranium. The horns in the Minotaura thingie appear broken, at least, but possibly artificial, although its possible they were authentic; the skull also possesses many smaller, nodular ornamentation of the skull in a pattern that is identical to Saichania chulsanensis. I would not allay horn similarities as relevant to synonymy, however, when every other aspect of the skull is virtually identical to Saichania chulsanensis, to which the holotype seems to belong, although I may be out on a limb there; this is especially relevant in the shape of the skull, and the elongated by flattened dorsal surface, instead of vaulting as in Pinacosaurus, as well as the smaller, more posteriorly-set orbits. But then, I only posted my take on the DML shortly after reading the paper, so maybe it got lost in the hubbub over the horns ;).

By Jaime A. Headden (not verified) on 16 Feb 2009 #permalink

Apparently the Minotaur had an undocumented mate.

That, or the taxon we've been discussing is actually "Minotaur-lizardless", whatever that means.

I think Jaime's right about the similarity with Saichania - the skull was originally identified as belonging to this taxon. I'm going to insert a comment on this into the text, thanks Jaime.

Davidd: the photos are hilarious, I especially like the one where Riddick is taking his ankylosaur for a walk.

That, or the taxon we've been discussing is actually "Minotaur-lizardless", whatever that means.

This is actually not stupid. After all, dinosaurs are not lizards. :-)

By David MarjanoviÄ (not verified) on 16 Feb 2009 #permalink

What I want to know is, are there audio recordings of the researchers performing the cranial collision experiments? It seems unlikely that the plastic models made appropriate noises, so it would have fallen to the experimenters to provide the requisite auditory effects.

By Nathan Myers (not verified) on 17 Feb 2009 #permalink

"I couldn't find a lungfish. Sorry.

Wow...I can't believe someone made a blog post out of my inane joke. Its even more hilarious with the pufferfish. I suppose I should finish the thing...

An ankylosaur, a lungfish, a salmon, and a cow walk into a bar. The four of them sit down to have a drink together, and the lungfish says to the Minotaurasaurus, "I swear, I can't tell the two of you apart". And the ankylosaur replies "well, I can't say you and the salmon don't look like brothers either".

I suppose that was some rather bad paleontology in-jokes. If anyone has a better ending, post it.

By Metalraptor (not verified) on 17 Feb 2009 #permalink

Regarding Nathan Myers' question, I don't recall making any noise when playing with the models. We were doing serious science with plastic dinosaurs, so any extra audio just wouldn't have been dignified! ;-)

I am somewhat entertained and dismayed that that fighting plastic dinosaurs paper published back in 2004 is perhaps my most cited publication. It's been tough for me to live that one down.

Zach - I assume you mean Horner & Goodwin (2006, 2008).

Horner, J.R., and M.B. Goodwin. 2006. Major cranial changes during Triceratops ontogeny. Proceedings of the Royal Society of London, Biological Sciences 273:2757-2761.

Horner, J.R., and M.B. Goodwin. 2008. Ontogeny of cranial epi-ossifications in Triceratops. Journal of Vertebrate Paleontology 28(1):134-144.

As for monospecific ceratopsids that are sexually dimorphic, it just doesn't work out. In nearly every case, the second species/morph is separated from its sister taxon in space and/or time. Something comes to mind about a beautiful hypothesis being slain by an ugly fact...

It would make no sense to say that "Nedo-" means a complete lack; the appropriate prefix would have been something like "Bes-" from "bez" (without). Russian "nedo-" from "ne do" (not upto; the same "do" meaning "until" in "do svidanija") compounded with a noun would imply a partial lack of the noun, i.e. an insufficiency, as in "nedobor" (shortfall) or "nedot[e/jo]pa" (a clumsy, not-very-bright person), except in cases where the noun requires completion, e.g. permission. (Compounding with a verb would imply a lack of completion of the action/activity.) If it matters, the meaning of "nedo-" in Ukrainian is similar, but tends toward a more extreme lack, at least in pejoratives, as in some pejorative Russian obscenities.

So, it is likely Ukrainsky means a lack in the partial sense. This would conform with "lacks [sic] of a prominent ..." above.

OTOH it would sound funny to say that something is without a horned face!

So, "incompletely horned face"? I suppose that makes something resembling sense.

By Andreas Johansson (not verified) on 18 Feb 2009 #permalink

All good stuff Darren! Lovely detail, and Witmer refs to look into... When I have time. Cheers!

By Graham King (not verified) on 19 Feb 2009 #permalink

[Holliday and] Witmer ref to look into... When I have time

Ha! I made time and read it... good stuff. Convinces me, anyway... [that the cranial kinesis advocated as a feeding adaptation in various dinosaur species requires firmer evidence thru more study].

By Graham King (not verified) on 19 Feb 2009 #permalink

And in latest news... there's Miragaia the sauropod-like stegosaur. A pity the rear half wasn't found. If only we could find even more complete material of dacentrurine stegosaurs...

Recently there was an ado about a new ankylosaurid called Minotaurosaurus. Darren Naish compared it to Pinacosaurus, others to Saichania. Neither is correct. Instead, it is a synonymy of Tarchia gigantea (PIN 3142/250, Tumanova 1977). Both ankylosaurids are characteristic with a straight skull roof anteriorly bent at 90 degrees in a premaxilla (Carpenter et al, 1998, modified ch23), with a strongly bumped surface (ibid, modified chs7, 8). The latter is also present in Saichania (Maryanska, 1977, Pl. 28), in contrast with Pinacosaurus and Euoplocephalus+Ankylosaurus, but Saichania has more rounded snout in profile, intermediate between Tarchia and AMerican taxa (Coombs, 1972, www.tyrellmuseum.com/tour/ankylo.html). Tarchia, Saichania and Pinacosaurus have 6 horns, 1 pair of jugal, supraorbital and post-orbital horns, in ANkylosaurus supra- and post-orbital horns are connected by a ridge. Pinacosaurus seems to be (a species of) Euoplocephalus.

Carpenter et al, 1998, presented a cladistic analysis of ankylosaurs with 26 characters, many of which are miscoded, inaprpriately used or gradual in both lineages.
3. wrongly coded for nodosaurs with no horns at top-rear corners (Gilmore, 1930)
5. Jugal horns absent in basal nodosaurs
7. untrue, cranial ornamentation is symmetrical in Tarchia and Saichania
8. very wrongly defined - ornamentation is smooth in Euoplocephalus, Ankylosaurus, Pinacosaurus etc, contra the authors Gargoyleosaurus is the only AMerican taxon with bumped surface
10. nares face anteriorly also in late nodosaurs
11. paroccipital orientation varies in Mongolian taxa (Tumanova, 1977)
12. probably also in late nodosaurs
13. "Tarchia differs from Saichania in that proximal portions of quadrate bones are not fused with paroccipital processes" (ibid)
14. miscoded for ankylosaurids, and all ankylosaurs have premaxillae below maxillae
15. gradual in both lineages, and miscoded for nodosaurs (SIlvisaurus premax teeth)
16. the same as 19.
18. contra the authors Gargoyleosaurus has premax+max 2nd palate, with pterygoids probably broken off therefore not contacting maxillae, miscoded for ankylosaurids, gradually evolved in both lineages, "Secondary palate in Tarchia yet developed fairly weakly in comparison with nodosaurids of Edmontonia type" (T, 1977)
22. already critices by Barrett et al
23. wrongly defined, miscoded for ankylosaurids - should be "straight skull roof", Dyoplosaurus (Gilmore, 1930) is not Euoplocephalus.
24. miscoded for late nodosaurids, gradual in both lineages

It is clear that both lineages evolved from a form with an open lateral temporal fenestra and sloped quadrate, straight skull roof and uncurved snout. The best candidate are aetosaurs, with Desmatosuchus showing the same dermal topology (with 1 pair of scutes and spikes on each side of column) on neck and shoulder region as in Sauropelta, a very similar though less modified skull and a strong supraglenoid process.

Peter Mihalda

By Peter Mihalda (not verified) on 26 Mar 2009 #permalink

Peter Mihalda: Wait, so are you saying that the ankylosaurs evolved from aetosaurs? So, do you mean that aetosaurs are actually dinosaurs? Or are ankylosaurs not dinosaurs then? And where do the stegosaurs and basal thyreophorans like Scelidosaurus fit in?

This could explain more:
Rauisuchids have been compared to carnosaurs by Galton (1985) but his own criterion (carnosaurs have a maxillary fenestra) does not work in Torvosaurus which skull is impossible to tell from eg Prestosuchus.
Rauisuchids have been united by aetosaurs (well, only Typothorax) by von Huene, and they share unambiguos synapomorphies:
- hyposphene-hypantrum
- laminated dorsals
- ?lesser trochanter on femur
- supracetabular crest
and probably other. In fact, here should "Dinosauria" be moved to Aetosauria+Rauisuchia, in order to keep the name. Phytosaurs, their sister group, share at least 2 characters with them.

Stegosaurs are thyreophorans, and their skulls are the most primitive for all thyreophorans, with an open antorbital fenestra etc. Mymoorapelta is a link between stegosaurs-ankylosaurs. For example, thyreophorans have 3 supraorbital bones (Gilmore, 1914, Maryanska, 1977) one of which is unquestionably the postfrontal, as in aetosaurs. Thyreophorans lack a palpebral (contra Coombs, 1972). Scelidosaurus is a thyreophoran, but with an open acetabulum and thus it cannot be an ancestor of any ankylosaur. It split off the main branch and gave rise to forms like heterodontosaurids and all other ornithischians. In my scheme, though, Lesothosaurus is a very derived form.

Peter Mihalda

By Peter Mihalda (not verified) on 29 Mar 2009 #permalink