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Re: [dinosaur] Dinosauria reclassification joins Ornithischia and Theropoda in Ornithoscelida



Thomas Michael Yazbeck <yazbeckt@msu.edu> wrote:

> Well, a lot of non-maniraptoran theropods (e.g. spinosaurids, some
> carnosaurs, _Deinocheirus_ and other ornithomimosaurs) have large claws that
> may have been used for other tasks than seizing small vertebrates - maybe
> they were defensive or used for intraspecific interaction/agonistic behavior
> (and herbivorous foraging in the ornithomimids).


Yes, I've also wondered if the large claws might have been used for
intraspecific combat or close-range defensive behavior (*very* close
range for short-armed theropods).  This could apply to the long-armed
therizinosaurs as well (after all, it's not as though they could run
away from a predator).

The long forelimbs and hands of derived ornithomimids might have been
suitable for hooking branches.


> Which leads me to another
> question, where exactly are ornithomimosaurs in the carpal evolution story?


The wrist bones of _Struthiomimus_ lack well-defined articular facets,
and formed a simple hinge-joint, capable of little or no rotation.
This is based on the work of Nicholls & Russell (1985; Palaeontol. 28:
643-677).

This same study also noted of the hand of _Struthiomimus_: "The
incipient coalescence of digits II and III, and their ability to be
strongly flexed suggests that they were enclosed in a common sheath of
skin".  This is of potential interest, considering this situation was
recently proven for _Anchiornis_ (specimen STM-0-144), with the second
and third fingers bound up in skin (Wang et al., 2017; DOI:
10.1038/ncomms14576).  So a functionally didactyl manus (with
syndactylous outer digits) might be primitive for Coelurosauria.  This
has repercussions for grasping abilities (or lack thereof) in
coelurosaurs.


> I know Ornithomimus has been shown to have pennate wing feathers.

Regarding the "pennaceous" feathers_of ornithomimid specimen TMP
1995.110.1 (not sure what genus it's currently referred to), this
interpretation has been disputed.  From Foth et al. (2014;
doi:10.1038/nature13467 Supp Info):

"In a recent article, Zelenitsky et al. (2012) hypothesized an
ontogenetic change in forelimb integument morphology in
_Ornithomimus_, from mono-filamentous feathers in juveniles to
pennaceous remiges in adults. However, this suggestion is speculative
and should be treated with caution, because no forelimb feathers are
actually preserved in the adult specimens described.  The only
evidence for feathers are pronounced linear carbonized markings on the
surfaces of the ulna and radius, which are three times wider than the
width of the filamentous feathers of the juvenile specimens.  These
markings were interpreted as traces of calami of long shafted
feathers.  However, even if the interpretation is correct, it
demonstrates only that the forelimb feathers of adult _Ornithomimus_
individuals were thicker and probably longer than those of juveniles,
but it unfortunately reveals nothing about the actual morphology of
those feathers.  The presence of more robust, mono-filamentous
feathers as present in cassowaries would produce similar traces and is
therefore also plausible."

So some sort of forelimb feathers were present in this ornithomimid,
possibly quite long; but the exact morphology of these feathers is
uncertain.