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Re: Dinosaurs burrowed to keep warm
Denver Fowler wrote:
>How many potentially burrowing ornithischians were present in the late
In north america: one.
(Warning: Unadulterated speculation coming up.)
I don't know which one Denver had in mind, but it depends upon how prevalent
this behavior was among ornithischians. _Thescelosaurus_ and _Bugenasaura_
were both late Maastrichtian "hypsilophodont"-grade ornithopods. Although
these two are outside the _Orodromeus_-_Oryctodromeus_-_Zephyrosaurus_ clade
(in Varricchio et al.'s analysis, anyway), burrowing behavior may have first
evolved much earlier in Ornithischia, as Dann suggested.
A _Zephyrosaurus_-_Orodromeus_ clade has been found before (e.g., Weishampel
and Heinrich, 1992), and was diagnosed by the presence of a jugal boss
(unknown in adult _Oryctodromeus_). It is possible that the jugal boss is
related to burrowing too (to help push dirt aside?). A jugal boss is also
seen in heterodontosaurs and many marginocephalians. Weishampel and
Heinrich (1992) proposed that the jugal boss is primitive for the
Ornithopoda+Marginocephalia clade (Cerapoda), but was secondarily lost in
most ornithopods (including the stiff-tailed iguanodonts). I'm not putting
too much stock in this single character, or its association with burrowing;
it's all just dodgy speculation on my part.
The thing is, burrowing behavior in _Oryctodromeus_ would probably not have
been inferred from anatomical evidence alone. The anatomy of
_Oryctodromeus_ was interpreted in light of the taphonomic evidence. The
anatomy of the closely related taxa (_Zephyrosaurus_, _Orodromeus_) was then
re-interpreted. If other ornithischian taxa turn up in burrows, then other
characters might be re-interpreted as burrowing characters too.
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