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*Jeholornis* (Archaeopterygiformes: Rahonavidae)??



(Just for the record... Archaeopterygiformes has never been defined, and
Rahonavidae has AFAIK never been published; DA mentions "rahonavids" a lot,
but this alludes to *Rahonavis ostromi* alone, and perhaps to undiscovered
relatives. The subject line just sounds impressive that way.)

HP Rutger Jansma wrote...

> I am talking
> about Jeholornis prima (tada!), a supposed arboreal proto-bird. Here I
will
> advocate that this other recently described is a arboreal basal Ovi of
some
> sort.
>
> The lower jaw was the first thing that made me think of this, this was so
> similair to the condition found in Caudipteryx, Incisivosaurus,
> Caenagnathids and Oviraptorids to a smaller degree,

I think it's hardly similar at all. The dentary is long and low, instead of
very high and short as in oviraptorosaurs (even *Incisivosaurus*, the least
extreme example).

> The second
> character observed in the skull is the reduced maxilla [...]

This sounds better. But it could be convergence because of selection for a
strong bite in the front of the jaw... and it's also present in all
avebrevicaudans with described skulls.

> Another feature in the
> skull, and this time the mandible, [...] is the well ossified symphysis.

Evolves easily when bite strength is needed more than intraramal mobility.
I'm sure your own dentary symphysis is fused. :-)

> The jugal shows a distinct curvature upwards,
> which approaches the condition seen in the Ovi's, but not totally, this is
> to be expected within a basal genus of a clade.

Assuming the jugal of *Jeholornis* is what the authors identify as such, it
is curved the opposite way of that of *Incisivosaurus*.

> Fifth, the near-mesopubic condition, which is a clear reversal from the
> condition seen in Archaeopteryx, which has a strong opisthopubic
condition.

To the contrary, *Jeholornis* is a bit more opisthopubic than both
*Archaeopteryx* and *Rahonavis*.

> Last, but not least, the similarities in the the caudal count. The reduced
> caudal count is something that appears to be almost diagnostic for the
> Enigmosaurs and this is best seen in genera like Caudipteryx and Nomingia
> were complete caudal counts can be observed.

*Archaeopteryx* and probably *Rahonavis* have similar counts, though, and so
do *Microraptor* and (less so) *Bambiraptor*. And they have very similar
tails -- transverse processes and neural spines limited to the first few
vertebrae, centra rather long, and chevrons and pre- & postzygapophyses that
provide stiffening, though by far not as much as in dromaeosaurs or
long-tailed pterosaurs. The last tail vertebra -- as long as the others and
pointed -- looks like in *Archaeopteryx*. Enigmosaur tails, on the other
hand, have well-formed, rather mobile tail vertebrae with neural spines and
transverse processes extending far behind (into the pygostyle of *Nomingia*,
at least the neural spines anyway).

> A pylogostyl is [...] not found in Caudipteryx

I'm still not totally convinced of that (though it's pretty certain that it
can't have had a pygostyle as big as that of *Nomingia*, and that has only 5
vertebrae). I'd need some very good illustrations of the last few
specimens... On the other hand, *Caudipteryx* could have been losing the
pygostyle, just like many flightless birds. How I wait for a second specimen
of *Protarchaeopteryx*...

*Jeholornis* shares with *Rahonavis* (and Ornithothoraces), but not
*Archaeopteryx* (or basal Avebrevicauda), the joint between scapula and
coracoid. The coracoid is longer than in *Archaeopteryx* and *Sapeornis*.
Apparently the fibula doesn't reach the calcaneum anymore as in *Rahonavis*
and Pygostylia, but again unlike *Archaeopteryx* and *Sapeornis*. The text
mentions a "hypertrophied second ungual" in the foot, I can't tell from the
photo.

I'll have to learn a lot more on ischium morphology...

> This has been my two cents...

You're underpaid.