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Re: Re: Segnosaurs (again)



Tom Holtz writes, in reponse to a question about segnosaurians:

>> I guess I was being a bit flippant when I made that comment.  A good
>> therizinosaurid skull would help resolve the issue of their eating
>> habits.  Which brings me back to a previous question - is any skull
>> material known for _Therizinosaurus_ or _Alxasaurus_?
>
> The former's skull is unknown, only the dentary is known of
> _Alxasaurus_.  Of course, _Erlicosaurus_'s skull is the best
> preserved of any Mesozoic theropod!!  The teeth of _Erlicosaurus_
> are "troodontiform" (pinched based and big denticles), which are
> morphometrically distinct from serration densities associated with
> vertebrate hypercarnivores (some sharks, basal synapsids, sabrecats
> of all stripes, varanoid lizards, pseudosuchians (including
> rauisuchids and xiphodont crocs), and most theropods).  This may
> indicate a non-hypercarnivorous diet (i.e., a diet which includes
> things other than vertebrate flesh, such as arthropods, molluscs,
> fungi, plants, etc.)

I wouldn't describe segnosaurian teeth as "troodontiform." They don't look at
all like the teeth of troodontids: just check the illustrations in _The
Dinosauria_ (pages 410-411).For one thing, there aren't any "blood pits" in
segnosaurian teeth. The isolated tooth figured by Russell & Dong in their
_Alxasaurus_ article scarcely resembles the teeth in the _Alxasaurus_
dentary, but that may be due to the sketchy nature of the figure of that
tooth. It looks as much like a small prosauropod tooth (see Galton's figures
in _The Dinosauria_) as it looks like a troodontid tooth, and I would even
question its identification as an _Alxasaurus_ tooth. (Not having seen the
specimens, however, I am sure I'll be corrected in due time by those who
have.)

Speaking of peculiar Mongolian dinosaurs, now that we have neck vertebrae and
teeth of _Alxasaurus_, why has nobody but me wondered whether the dinosaur
described by Gilmore in 1933 as _Mongolosaurus haplodon_, an aberrant
sauropod, is a segnosaurian? The _Mongolosaurus_ material looks quite a bit
like _Alxasaurus_, though differing in details as might be expected of a
distinct taxon.