[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: At long last! Turner, Makovicky & Norell on dromaeosaurids

Consider at least that, if Senter's analysis is correct (as has been followed 
since), *Incisivosaurus gauthieri* should have a postcrania much like that of 
*Protarchaeopteryx robusta*: short tail, longish neck, lanky legs, and 
relatively long arms. Compared to the body proportions of microraptorians, 
which have a very long tail to compensate their total body length. I'm not 
quite sure about the effectiveness of even large sterna when they are not fused 
to one another, and if we presume this is the adult condition (size disparity 
may suggest this wasn't the case), the shoulder apparatus would have been 
highly unstable for holding the limbs out for any sort of sustained flapping or 
even gliding.


  Jaime A. Headden
  The Bite Stuff (site v2)

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 

> Date: Sun, 26 Aug 2012 18:46:51 +1000
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: At long last! Turner, Makovicky & Norell on dromaeosaurids
> Jason Brougham <jaseb@amnh.org> wrote:
> > This may be my fault. I may have started this by saying that Incisivosaurus 
> > (the most basal known oviraptorosaur) is not very flighty. Then someone 
> > compared
> > Incisivosaurus to Protarchaeopteryx. What I meant is that Incisivosaurus is 
> > big and relatively heavy.
> No worries, Jason. I agree with you that size alone makes
> _Incisivosaurus_ very un-"flighty" indeed. However, it is more than
> likely that the aerial behaviors of many basal paravians were very
> different we see today among extant gliding and flying vertebrates.
> Being a bit on the heavy side might not have been a problem for
> maniraptorans - especially if incipient wings were used for
> orientational control during controlled descents ("parachuting")
> rather than extending the glide path. Of course, we don't yet know if
> _Incisivosaurus_ had an any kind of aerial ability at all, because we
> don't know what kind of feathers it had.
> > Incisvosaurus' skull is 11cm long, while Sapeornis' skull is 6 cm long 
> > (IVPP V13275 and IVPP 13276) and Protarchaeopteryx is 7 cm (NGMC 2125).
> The skull of _Incisivosaurus_ (which the original description puts at
> about 10 cm) was not much larger than that of _Microraptor hanqingi_,
> which was maybe around 9.5 cm long. Then again, we can't be sure that
> the latter glided either.
> > And, yes, that is interesting about Sapeornis moving down the phylogenetic 
> > tree in Turner et al. 2012.
> Yes, _Sapeornis_ had a shoulder anatomy that was not too different
> from that of _Archaeopteryx_ - but a tail that was extremely short,
> and fused at the end to form a pygostyle. _Sapeornis_ shows some
> adaptations for perching, especially the large hallux and J-shaped
> metatarsal I (so the attached digit would be directed more posteriorly
> compared to if the metatarsal I was straight, as in _Archaeopteryx_
> and non-avialan theropods). If _Sapeornis_ spent much of its time in
> trees, eating seeds (for which we have direct evidence, with two
> specimens each showing a seed-filled crop), it could have used its
> wings to glide from tree to tree. A long tail was perhaps of little
> (if any) use for an arboreal bird, so it was drastically shrunk and
> fused to form a pygostyle in _Sapeornis_. The pygostyle could have
> supported a rectricial fan, as in much more advanced birds; but it's
> more likely that the tail of _Sapeornis_ was aerodynamically
> redundant, as in confuciusornithids.
> By contrast, _Archaeopteryx_ and _Jeholornis_ have long tails (by
> avialan standards), which is consistent with the interpretation that
> these basal avialans were predominantly terrestrial. The long tail
> was there to help counterbalance the animal when running on the
> ground. The frond-like arrangement of rectrices served to support the
> tail during aerial locomotion (gliding?). But a better strategy was
> simply to truncate the tail skeleton altogether, and get it out of the
> way. But this was difficult for cursorial animals that still had a
> fairly cranial center of mass, and hip-based stride generation, and
> needed a long tail for balance. The pygostyle-like structures of
> certain non-avialan maniraptorans (_Beipiaosaurus_, _Nomingia_,
> _Similicaudipteryx_) were not accompanied by the profound truncation
> of the tail we see in _Sapeornis_, confuciusornithids, and more
> derived short-tailed birds.
> Also, the presence of a crop in _Sapeornis_ means that this feature
> may be present in the seed-eating avialan _Jeholornis_, which Turner
> &c recover as more derived than _Sapeornis_.
> Cheers
> Tim