tag:blogger.com,1999:blog-3248412803814730250.post411373418322331837..comments2024-03-17T01:48:59.504-07:00Comments on The Theropod Database Blog: SVP 2014 Day 3- drepanosaurs and sauropodsMickey Mortimerhttp://www.blogger.com/profile/08831823442911513851noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-3248412803814730250.post-87322176556608803302014-11-10T10:16:54.254-08:002014-11-10T10:16:54.254-08:00Wouldn't it be funny if pterosaurs were relate...<i>Wouldn't it be funny if pterosaurs were related to drepanosaurs, and thus non-saurians convergent on archosaurs? Even crazier than them being lizards.</i><br /><br />Quite! This idea wasn't mentioned in the talk, but diapsid phylogeny (and amniote phylogeny in general... and it goes farther...) is a much bigger mess than most people think.<br /><br /><i>another titanosaur that I was told about during the conference and that could be much more important for the Nemegtosaurus-Opisthocoelicaudia problem than my seven isolated fossils</i><br /><br />Oho!David Marjanovićhttps://www.blogger.com/profile/00233722577300632805noreply@blogger.comtag:blogger.com,1999:blog-3248412803814730250.post-51243959835268112602014-11-10T00:57:31.908-08:002014-11-10T00:57:31.908-08:00Hi Daniel, thanks for the reply. I agree they cou...Hi Daniel, thanks for the reply. I agree they could be synonymous, I just don't think that two caudals and five unguals makes it much more likely. <br /><br />The first issue, which you probably address in your MS, is how diagnostic Opisthocoelicaudia's caudal centra and pedal unguals are. Can the isolated centra and unguals be distinguished from those of other titanosaurs? Besides vulcanodontids, I don't think I've ever read a suggestion that sauropod pedal unguals can be referred to a particular clade, let alone a particular genus. Caudal centra seem a bit more likely to be diagnostic, but also vary within the tail. There are several titanosaur genera that are based on the entire caudal vertebra and which are considered undiagnostic (Titanosaurus, Iuticosaurus, etc.), though I could imagine Opisthocoelicaudia having a unique combination of caudal central characters. The caudal series and skull you mention seem much more likely to be diagnostic once they're described. But Kurzanov (1981) originally thought he had a new Nemegtosaurus skull too, and it ended up being distinct and described as Quaesitosaurus. So I don't put much weight in unjustified referrals.<br /><br />The second issue is the statistical one. Even if all seven specimens are Opisthocoelicaudia, how many Opisthocoelicaudia specimens do we need before we can say there probably isn't another kind of Nemegt titanosaur postcranium out there that hasn't been found yet? I'd say more than seven, though I admit that's just my gut feeling and not an objective measure. That's what the Tarbo:Deino ratio was supposed to illustrate- if we can find 35 Tarbosaurus' and only 1 Deinocheirus, surely it's not a stretch to find 8 Opisthocoelicaudia's and only 1 Nemegtosaurus. I didn't know about the second reported Nemegtosaurus skull though, and if that's correctly identified, I think it strongly supports your case. If every skull found is Nemegtosaurus and every postcranium found is Opisthocoelicaudia, that becomes too coincidental to ignore, even with relatively few specimens. I don't think 2 skulls are enough to make it probable, but I'd be convinced at 4 skulls and 4 postcrania. I think that'd be a 1.5% chance of being a coincidence.<br /><br />And yeah, I'd love to see your MS. Just send it to Mickey_Mortimer @ msn.com . Also that's cool that you tried combining the OTUs. The important metric there would be how much longer that tree is than when they're kept separate.Mickey Mortimerhttps://www.blogger.com/profile/08831823442911513851noreply@blogger.comtag:blogger.com,1999:blog-3248412803814730250.post-67740718216639215032014-11-09T09:45:25.211-08:002014-11-09T09:45:25.211-08:00I'm very well aware of the existence of Boreal...I'm very well aware of the existence of Borealosaurus (and another titanosaur that I was told about during the conference and that could be much more important for the Nemegtosaurus-Opisthocoelicaudia problem than my seven isolated fossils) :) I'm also well aware of the fact that several different sauropods might be present at the same environment. Likewise, I know that it would be much better if we also know more about the holotype of Quaesitosaurus orientalis (I've seen it while I was at the RAS paleo museum but it was behind a glass and I couldn’t actually examine anything), the undescribed sauropod dorsals from Gobi (also at the museum; I didn't get permission to study it), or the second skull that is supposedly referable to N. mongoliensis (Maryańska 2000).<br /><br />The fact that we don't know as much as we want to, however, doesn't mean that we should overlook the issue of the probable conspecificity of Nemegtosaurus and Opisthocoelicaudia. ;)<br /><br />Oh, and I don’t understand how the Tarbosaurus-Deinocheirus fossils ratio can be an argument. I think that I wouldn’t be surprised if somebody talks about it when Nemegtosaurus is still considered diplodocoid. But it’s not. It’s a derived titanosaur. By the way, when both OTUs are merged, the “new” Nemegtosaurus is inferred at the position previously occupied by Opisthocoelicaudia (and the tree topology is almost unchanged while compared to the “traditional” interpretation of these taxa).<br /><br />Anyway, my MS on the topic is already written and since I prefer to include the discussion of as much arguments as possible, I would be very happy if you were interested in reading it. I respect your opinions and it might help me to clear up my points. So, let me know if can I send it to you.<br /><br />Refs<br />Currie, P. J., Badamgarav, D., and Koppelhus, E. B. 2003. The First Late Cretaceous Footprints from the Nemegt Locality in the Gobi of Mongolia. Ichnos 10: 1–12.<br /><br />Maryańska, T. 2000. Sauropods from Mongolia and the former Soviet Union. In Benton, M. J., Shishkin, M. A., Unwin, D. M., and Kurochkin, E. N. (eds): The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press, 456–461, Cambridge.<br /><br />Nowiński, A. 1971. Nemegtosaurus mongoliensis n. gen, n. sp. (Sauropoda) from the uppermost Cretaceous of Mongolia. Palaeontologia Polonica 25: 57–81.Daniel Madziahttps://www.blogger.com/profile/13227952268357983494noreply@blogger.comtag:blogger.com,1999:blog-3248412803814730250.post-63607246041392133662014-11-09T09:44:54.416-08:002014-11-09T09:44:54.416-08:00Hi Mickey,
I write my response in two posts becaus...Hi Mickey,<br />I write my response in two posts because Blogspot doesn't allow me to publish the text as a whole. It seems that it also prefers keeping things separate rather then merged into one :P<br /><br />I'm surprised and super happy at the same time that my poster (not a talk) gained so much attention. I didn't expect it :) This is the first comment that explicitly disagrees with my conclusions (saying that, given the data we have, Nemegtosaurus and Opisthocoelicaudia are most likely synonymous). But that's OK. As I told to everybody with whom I was discussing this during the conference (too bad you weren’t there), the goal of this poster was to force people to discuss the issue and take it into account in their papers. And I seem to be successful (at least with the first part). :) If I’m proven wrong in my interpretation of the sauropod material from the Nemegt Formation, I'll be perfectly satisfied as well :)<br /><br />When I started my MSc studies in Warsaw, I wanted to look at "nemegtosaurids" and try to add something new to our knowledge of the interrelationships of advanced titanosaurs. However, this was later changed to the question of the possible synonymy of Nemegtosaurus and Opisthocoelicaudia. I wasn't very satisfied with that as I felt that the most important things were already discussed in the literature. And since the most often conclusion was that we simply need an articulated specimen that includes the Nemegtosaurus-type skull with the Opisthocoelicaudia-type postcranial skeleton, I didn't expect that my thesis will actually change anything. As the type of N. mongoliensis is at the collections of the Polish Academy of Sciences, I had also access to the other dinosaurs from Mongolia, and I noticed that there is additional seven sauropod specimens from different localities of the Nemegt Formation. The unguals and the very slightly opisthocoelous mid-caudals are indistinguishable from the type of O. skarzynskii.<br /><br />And then there is the skull. Nowiński (1971) described N. mongoliensis as a Dicraeosaurus/Diplodocus-like sauropod and for many years it was viewed as such. But the papers from the late nineties and on show that it's a typical titanosaur. Though, its ties to other taxa are often very weakly supported.<br /><br />Meanwhile, Currie et al. (2003) writes about a series of opisthocoelous caudal vertebrae and footprints from the type locality of N. mongoliensis that they refer to Opisthocoelicaudia.<br /><br />So, every single fossil from the Nemegt Formation belonging to sauropod postcranial skeleton, mentioned after the description of Nemegtosaurus and Opisthocoelicaudia, suggest that there is only one sauropod.<br /><br />Is my reasoning really "highly flawed" when I say that I see no reason for keeping these taxa separate? In other words, is the skull really so special that the assumption that it fits the skeleton of Opisthocoelicaudia is that improbable?Daniel Madziahttps://www.blogger.com/profile/13227952268357983494noreply@blogger.comtag:blogger.com,1999:blog-3248412803814730250.post-36064403201355048672014-11-09T06:22:09.487-08:002014-11-09T06:22:09.487-08:00Yes, yes. I'll change that once I change BMNH...Yes, yes. I'll change that once I change BMNH to NHM. Museums should really consider Google when they decide to change acronyms. Makes tracking information MUCH harder.Mickey Mortimerhttps://www.blogger.com/profile/08831823442911513851noreply@blogger.comtag:blogger.com,1999:blog-3248412803814730250.post-9436801126305052392014-11-09T06:12:32.152-08:002014-11-09T06:12:32.152-08:00"Moved to the IGM[...]"
It was moved to..."Moved to the IGM[...]"<br /><br />It was moved to the MPC. The name "IGM" only exists in the AMNH papers, whereas all other resources, including the resources in which the name change was first pointed out, indicate that the old Mongolian Geological Institute (various abbreviations including: GI, GIN, IGM) was formalized to "Mongolian Paleontological Center" (or MPC) for the purposes of not interfering with the name of another museum.Anonymousnoreply@blogger.com