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Re: _Microraptor zhaoianus_



Before I write a details segment on Microraptor and include it in my
phylogenetic analysis, I thought I'd comment on its size.  It is touted as
the "smallest known non-avian theropod dinosaur", but is it?  First of all,
the authors claim it is an adult.  This is based on the fused sacral
vertebrae, the pubic symphysis, partial fusion of the last dorsal to the
sacrum, fine tooth serrations, well-ossified cortical bone, well-developed
accessory trochantor, small skull/femur ratio and small sacrum/femur ratio.
However, according to Nick Longrich, an accessory trochantor is
characteristic of subadult maniraptorans, such as the holotype of
Microvenator.  Also, the usefulness of "adult" bone texture in determining
age has been recently questioned by Tumarkin and Dodson (2000, at SVP) based
on comparison to living crocodilians.  So I would feel more comfortable with
this specimen being a subadult, but let's assume it's an adult for the sake
of arguement.  Is it the smallest non-avian theropod?  Luckily for us, the
question of which non-avian theropod is smallest was asked just a few months
ago in August.  The femur of Microraptor is 53 mm long.  The previous record
holder was Parvicursor (52.6 mm).  Caenagnathasia and Saltopus had smaller
femora, but the former's length must be estimated (~40 mm) and the latter is
probably non-dinosaurian.  So Microraptor and Parvicursor had femora of VERY
similar size.  Which one was larger comes down to vertebral and cranial
proportions.  The small skull of Microraptor might suggest it had a long
neck, like alvarezsaurids, and both alvarezsaurids and Microraptor have
caudal/femoral ratios of 4.4/1.  Seems like a close match to me.  Perhaps
Parvicursor and Microraptor should be tied for smallest non-avian theropod
until we get more precise data.

Mickey Mortimer