Denver Fowler wrote:
>How many potentially burrowing ornithischians were present in the late
>Maastrichtian?
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.
Cheers
Tim
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