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Re: New reference, dinosaur polyphyly based on track record
> That doesn't make much sense to me. Of course the unique morphologies
> of later theropods, sauropodomorphs, and ornithischians wouldn't be
> present in the very earliest members. Dinosaurs would be polyphyletic
> if you used _Theropoda_, _Sauropodomorpha_, and _Ornithischia_ as
> pedal apomorphy-based taxa and defined _Dinosauria_ as _Theropoda_
> plus _Sauropodomorpha_ plus _Ornithischia_ *and nothing else*. But
> that is not how the taxa are defined.
> Maybe there's more in the paper, but it sounds like he's talking more
> about the subsequent differentiation of theropods, sauropodomorphs,
> and ornithischians than the actual origin of dinosaurs.
Even though the geosciences library in Vienna does not carry Ameghiniana, it
does carry Alcheringa, so I've read the paper. It seems to have taken a very
long time from submission to publication. Its basic premises are outdated:
- The paper assumes that all three-toed tracks come from theropods or at most
dinosauromorphs. *Effigia* and the new *Poposaurus* specimen reported at this
year's SVP meeting argue otherwise.
- There are tracks with big 3-toed hind prints and small fore prints whose
fingers point forward. The paper attributes them to theropods -- but theropods
_retain_ the _inability_ to pronate their forearms, so fore prints with
forward-facing fingers _cannot_ come from a "theropod", including all
theropod-shaped non-ornithischian dinosauromorphs. Indeed, some or all of these
(*Atreipus*) have been referred to ornithischians years ago (Lockley's books).
(What do I know -- maybe they, too, are from "poposaurids".)
- The Dinosauria II is not cited. The Basal Saurischia chapter of that book
contains a convincing demonstration of saurischian monophyly -- Thulborn
doesn't mention it. Instead, he relies on the late Charig (!) for morphological
arguments against dinosaurian and saurischian monophyly; keep in mind that
several of these were just reasoning of the kind "any character that could
imaginably have evolved twice must not be used as evidence for the monophyly of
any taxon" and firmly grounded in a lack of understanding of cladistics.
- Even the realization that the Ornithosuchidae is not on the ornithodiran side
of the tree but on the crurotarsan one is not mentioned.
- In sum, it is perhaps no wonder that the paper acts as if the sauropods sensu
stricto came out of nowhere (and uses this to argue that it's perhaps easier to
derive them directly from primitively quadrupedal archosaurs). The
demonstration that *Anchisaurus* is a sauropod is not mentioned.
- *Pisanosaurus* is not accepted as an ornithischian (I think D2 would have
helped here, too). Of course the unnamed Triassic specimen mentioned in the
description of *Stormbergia* was unknown to Thulborn as well, so he claims
there's no evidence of Triassic ornithischians at all. IIRC, vague speculations
about Phytodinosauria are mentioned.
That's why I didn't try to direct attention to it. :-)
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