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Re: segnosaurs



In a message dated 96-02-28 10:37:04 EST,
T.Williams@cclru.randwick.unsw.edu.au (Tim Williams) writes:

>While on the subject of segnosaurians - WHAT ON EARTH ARE THEY?  Since 
>their discovery (what - ?twenty years ago) they've been regarded as 
>(1) aberrant theropods, (2) relicts of a prosauropod-ornithischian 
>transition, (3) saurischians close to sauropodomorphs.  Now, as I 
>understand it, segnosaurians are regarded as advanced 
>coelurosaurians, with even a few bird-like characters found in the 
>braincase.  What's the consensus on the Segnosauria?  (Is there 
>one??)  These critters fascinate me.

Segnosaurian remains have proved to be fairly common in Cretaceous rocks of
the eastern republics of the former USSR, according to Nessov's 1995
monograph on Russian dinosaur localities. The earlier remains represent
rather small forms, the later remains include _Plateosaurus_-size
segnosaurids and the even larger therizinosaurids. Nessov suggests that the
smaller, earlier segnosaurs lived in trees eating wasp's nests (a form taxon
he calls _Desertiana_; the wasp larvae would provide a protein-rich source of
nourishment), and the larger, later segnosaurs on the ground. The analogy he
pursues is tree sloth and megathere ground sloth. This is an elaboration of a
hypothesis put forward around 1972 by Rozhdestvensky, before segnosaurs were
recognized as a distinct dinosaur group, to account for the large-clawed,
large-forelimbed therizinosaurids and deinocheirids being discovered in
eastern Asia: The large claws were for holding the creatures upside-down,
hanging sloth-like from trees. Most paleontologists have ignored
Rozhdestvensky's paper, or have cited it as some kind of fringe paleontology.