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

New studies refute Oregon State hypotheses

As we all know, in 1997 the Oregon State group jumped the gun by presenting
number of conclusions on theropod anatomy and relationships vis-a-via birds,
before they examined the Sinosauropteryx specimen they based some of their
conclusions on. As we get deeper into 1998 a number of more careful studies
are deconstructing their notions. These are Chen et al's (Jan 8 Nature) long
awaited description on Sinosauropteryx, Norell & Makovicky's (Dec 31 AMNH
Novitates) description of a 3-D preserved pelvis, and Padian & Chiappe's (Feb
Sci Amer) article on bird origins. 

At SVP, 

Geist et al argued that the fibers adorning Sinosauropteryx were internal
collagon fibers that supported a dorsal frill adapted for swimming. They had
no actual data that this was true, but it did fit their preconception that
theropods were not insulated endotherms (that generated the majority of their
body heat internally). Chen et al. have laid that idea to rest. The fibers
are clearly external, and judging from their distribution on the head, neck,
body, tail, arms and legs densely covered almost the entire body. To this
data can be added the Protoarchaeopteryx photos presented in Padian &
Chiappe. The lack of a reversed hallux, among other things, shows that it is
a theropod. One with well developed contour feathers (confirmed by a better
second specimen). The question now is whether the bristles on these theropods
were true, albeit early feathers. Those who are actually working on the
specimens will provide the real answers. In any case we can chuck the
collagon frill hypothesis into the water. 

Ruben et al. (Nov 14 Science) claimed that the type Sinosauropteryx specimen
had a croc-like septum. In postings Jones asserted that all 3 of them had the
septum. As for the type, breakage and preparation obscures most or all of the
alledged border of the dark region, so it is impossible to tell whether or
not a semi-circular arc exists. Actually, you could tell this just by looking
at good photos, but it has been verified by recent direct examination of the
specimen. As for Jones claim that the other specimens show the septum, the
high quality photos in Chen et al. of the second specimen clearly show that
there is no trace of the thing. Nor, according to those who have seen it, is
any septum present in the third specimen. There is not the slightist bit of
soft tissue evidence for a croc-like septum in any theropod skeleton. 

Ruben et al. asserted that Archaeopteryx had a more retroverted pubis than
any theropod, and that all of the latter had nonretroverted pubes suitable
for anchoring croc-like diaphragmatic muscles. In doing so they failed to
appreciate the work by Wellnhofer, Perle and Barsbold showing that some
dromaeosaurs had pubes more strongly retroverted than the urvogel. This fact
is reconfirmed by the new pelvis in Norell & Makovicky. Now, since some
dromaeosaurs, as well as advanced alvarezsaurs, had highly retroverted pubes,
how could they anchor croc-like respiratory muscles? Answer, they could not.
The sheer amount of variation in pubic retroversion between closely related
theropods (the pubis is subvertical in some sickle claws - Unenlagia,
Malagasy dino-bird - and highly retroverted in others - Velocirpator; there
is similar variation in alvarezsaurs as noted by Leahy in his recent post)
argues that it is not important to the function of the respiratory system
like it is in crocs. As I noted in PDW back in 88, the long pubis probably
swings back and forth in order to best balance the body mass as abdominal
versus tail mass changes.    

When this is all sorted out, it's going to be proven (in the sense of the
therapsid-mammal link) that birds are theropods, that theropods had a
pre-avian not croc-like respiratory complex, that the latter was ventilating
an elevated aerobic capacity approaching and equalling the kiwi level, and
that the heat was being retained via hollow bristle feather insulation.

For whom does the bell toll? It tolls for the nontheropodian hypotheses of
bird origins.