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Dinosaur Park Troodontids; Stenonychosaurus is back!
Topic Started: Aug 11 2017, 04:17 AM (466 Views)
Dapper Man
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Stenonychosaurus is back, along with the new species, Latenivenatrix!
Idk if you've seen this before, but it's some interesting stuff, guys!
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Archeoraptor
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Trodoon may no longer be a genus, but Troodontidae is valid even if Troodon isn't
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kusanagi
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Troodon always was problematic enough to be regarded as a lizard, a pachycephalosaur and even as a carnivorous ornithopod. (Which tells us something about the bonehead "herbivores" really. Does anyone think most ornithischians were vegetarians? I don't.) If someone can declare Tyrannosaurus has priority or Scelidosaurus is valid, they can stop people identifying whole animals for controversial and vastly incomplete holotype specimens. Naming teeth is fine but genus Troodon has caused far too much confusion already.
Edited by kusanagi, Aug 11 2017, 11:05 AM.
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LittleLazyLass
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a pachycephalosaur and even as a carnivorous ornithopod.
Back when this was the leading idea pachycephalosaurs were considered to be ornithopods, so this is actually the same thing.
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kusanagi
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Aug 12 2017, 10:38 AM
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a pachycephalosaur and even as a carnivorous ornithopod.
Back when this was the leading idea pachycephalosaurs were considered to be ornithopods, so this is actually the same thing.
Not quite, at least in pop sources T. was described as a carnivorous hypsilophodont(!) including the diagram group's famous line art of a T. biting a lizard. Pachycephalosaurs - as you know - combine a vast hindgut with generalised dentition as seen in clades of lizards that eat anything from insects to green vegetation. Therefore as with large thyreophorans there is mismatch between the crudely developed teeth and advanced hindgut (extending into the tail basket in pachycephalosaurs?) though the exact diet is unknowable and perhaps variable. Ornithopods on the other hand are interpreted as strict herbivores though when Headden compared ornithischian teeth to those of herbivorous mammals, he found most hypsilophodont-grade ornithopods similar to duikers ie. habitual faunivory cannot be excluded though even if so, they were primitively and prefominantly herbivorous. Jeholosaurus for example has fangs or tusks that might have been used in prey capture but these were small prey, and the alternative uses were defence or interspecific combat. Claims that Muttaburrasaurus was a carnivore do not really stand up as they rested on shearing edges of the teeth: in living animals, shearing does not demonstrate carnivory. Ditto for the horned dinosaurs too often interpreted nowadays as large omnivores though their population density and ecology puts them in the herbivore guild.

In total ornithischians, except the most plesiomorphic forms perhaps, were herbivores but not necessarily obligate herbivores except in the most specialised clades, and dietary composition may have changed with ontogenetic stage (least likely in altricial taxa such as hadrosaurids). No known ornithopod or ornithischian demonstratedly ate meat, fish or insects though it is possible or even predicted.But this hasn't stopped speculations such as the mid interpretation of Troodon in the past.
Edited by kusanagi, Aug 12 2017, 11:04 AM.
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IIGSY
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Why don't we just change stenonychosaurus to troodon? It seems simple.
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Aug 29 2017, 05:50 AM
Why don't we just change stenonychosaurus to troodon? It seems simple.
Because it's not simple. Troodon does not have enough holotype material to accurately judge what is or isn't troodon, so is a dubious genus until redescribed from more complete remains. Since the Stenonychosaurus holotype is more complete, we are using that to describe the troodontid remains we have currently, other then remains of species under a different genus the troodontid remains.
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kusanagi
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If you can't tell for sure if a new animal is the same as an already described, poorly known or preserved one, then you CANNOT tell if they are the same taxon. You cannot measure one of the two properly to compare them. QED.

Why do people have to explain and debate some things? Part-organismal remains are prone to be problematic and if they are poorly preserved it is even worse.
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kusanagi
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Insect: why were Monoclonius and Trachodon removed from popular and scientific dinosaur books? Trachodon was an edmontosaurine and monoclonius a centrosaurine but its impossible to be more certain than that so the usage dropped: no one can know which dinosaur was the real Trachodon or Monoclonius. Same with Troodon, its nothing unique.

Someone mentioned Manospondylus in the other thread: yes, Tyrannosaurus rex is a definite junior synonym of Manospondylus gigas, but after year 2k an arbitrary rule stated taxa considered nomen dubia for half of a century cannot take priority. But the vertebra is considered as T. rex. Its a very different situation than with Troodon. Or Brontosaurus, which is a junior synonym (or a subgenus?) of Apatosaurus.
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Only it isn't like that for Brontosaurus. We know what species the type specimen of Brontosaurus belonged to, and a phylogenetic analysis in 2015 shows that it was less closely related to Apatosaurus than Apatosaurus was to Supersaurus. This means that unlike Monoclonius and Trachodon, which are abandoned because we don't know what species they actually were, Brontosaurus is here to stay.
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trex841
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Wait, what is this about Troodon not being a valid genus? This is the first I'm hearing of it.
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kusanagi
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Scrublord: yes I was contrasting the three situations, those of problematic tooth taxa, of a junior synonym, and of an unrecognised senior synonym.

B. is so similar to Apatosaurus to the point its a matter of lumping or splitting. Apatosaurines are particularly heavy, grazing sauropods with a tendency toward a shorter neck than the diplodocines. But then again I admit that I know little about the sauropods: its just the diplodocine-apatosaurine split (just two genera?) is old hat by now. Supersaurus has been problematic with recent topologies placing S. at the base or within the apatosaurinae. (Its unknown.)
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LittleLazyLass
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Why don't we just change stenonychosaurus to troodon? It seems simple.

Because they're tied to two different holotypes. We have no way of knowing if these two specimens represent the same species, because the Troodon holotype lacks diagnostic characters making it distinguishable from specimens of more than one other named species.

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Someone mentioned Manospondylus in the other thread: yes, Tyrannosaurus rex is a definite junior synonym of Manospondylus gigas

No it isn't, that's why Manospondylus gigas is a nomen dubium. Now, more of the holotype specimen was apparently discovered, but that's not been published, so it can't (yet) be used to demonstrate the species is conspecific with Tyrannosaurus rex.

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but after year 2k an arbitrary rule stated taxa considered nomen dubia for half of a century cannot take priority.

No such rule exists; you're referring to the case of nomina oblita, which, once again, can't apply to a dubious taxon. Matt Martyniuk explains the rule here, although is under the same incorrect presumption that M. gigas is referable to T. rex. Of course, it obviously is T. rex, the idea there was some unknown other gigantic Hell Creek tyrannosaur is ridiculous, I'm not saying otherwise, but scientifically, it cannot be distinguished as such.

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Or Brontosaurus, which is a junior synonym (or a subgenus?) of Apatosaurus.

For a few years now Brontosaurus has been considered a valid genus as per Tschopp et al. (2015), because it's the exact same situation as Stenonychosaurus - it was generally (but not always) considered a distinct species with the other genus (Troodon/Apatosaurus), and now we've realized that placing them in the same genus doesn't hold up, albeit for different reasons.

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and a phylogenetic analysis in 2015 shows that it was less closely related to Apatosaurus than Apatosaurus was to Supersaurus.

No it didn't, that analysis recovered Supersaurus as a diplodocine congeneric with Dinheirosaurus (i.e. the latter should be Supersaurus lourinhanensis, although since Supersaurus might be dubious as per Taylor, I wouldn't go with this for now). In their analysis Brontosaurus and Apatosaurus are still sister taxa, the only currently recognized apatosaurines, but determined through a methodical approach that they are dissimilar enough to be separate genera. Brontosaurus actually has three species now, too. Here's the actual paper here, it's kind of a landmark in diplodocid research.

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Wait, what is this about Troodon not being a valid genus? This is the first I'm hearing of it.

Most everyone has admitted Troodon formosus is probably not diagnostic with respects to other North American troodontids for years now, but a paper finally bit the bullet and formally declared it a nomen dubium, and therefore revived Stenonychosaurus as a valid genus for the species we used to call Troodon inequalis.

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B. is so similar to Apatosaurus to the point its a matter of lumping or splitting.

Tschopp et al. (2015), which I linked earlier in this post, didn't just subjectively decide that they were going to consider B. excelsus, B. parvus, and B. yahnahpin a separate genus. They used a distinct methodology to demonstrate that they should be. Again, go read the paper, it's explained there.

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Supersaurus has been problematic with recent topologies placing S. at the base or within the apatosaurinae. (Its unknown.)

The 2015 study is a landmark and there's very little reason not to trust their topology over all others for the time being.
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