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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.

On 11/21/06, Mark Van Tomme <markvantomme@yahoo.com> wrote:

I came across this reference today,I've checked the archives and apparently no one has posted on this paper, so here it is :-)


Regards

Mark Van Tomme


THULBORN, T., 29.9.2006. On the tracks of the earliest dinosaurs: implications for the hypothesis of dinosaurian monophyly. Alcheringa 30, 273-311.

>From the record of dinosaurian skeletal remains it has
been inferred that the origin and initial
diversification of dinosaurs were rapid events,
occupying an interval of about 5 million years in the
Late Triassic. By contrast numerous reports of
dinosauroid tracks imply that the emergence of
dinosaurs was a more protracted affair extending
through much of the Early and Middle Triassic, This
study finds no convincing evidence of dinosaur tracks
before the late Ladinian. Each of the three
dinosaurian clades - Theropoda, Sauropodomorpha,
Ornithischia - produced a unique track morphotype that
appears to be an independent modification of the
chirotherioid pattern attributed to stem-group
archosaurs (thecodontian reptiles). The existence of
three divergent track morphotypes is consistent with
the concept of dinosaurian polyphyly but can be
reconciled with the hypothesis of dinosaurian
monophyly only by invoking many and rapid reversals in
the locomotor anatomy of early dinosaurs. The origin
of dinosaurs was not the correlate or consequence of
any single event or process, be it global change,
competitive replacement, or opportunism in the wake of
mass extinction. Instead the origin of dinosaurs is
envisaged as a series of three cladogenetic events
over an interval of at least 10 million years and
possibly as much as 25 million years. This scenario of
dinosaurian polyphyly is as well-supported by fossil
evidence as is the currently favoured view of
dinosaurian monophyly.




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