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pubic boots and hepatic piston lungs
John Ruben gave an interesting talk here at UC-Berkeley last week.
He has an interesting hypothesis about dinosaur lung anatomy, especially
for theropods (I'm not saying I agree [I don't], but it's interesting). In
case you haven't heard it yet, here's a short overview; I hope it's clear
Ruben believes that non-avian dinos (and perhaps archosaurs
primitively) had a hepatic-piston type of lung, like modern crocs do.
According to him, the lungs are pumped in a piston-type action by the /m.
diaphragmaticus/, moving the liver in the process (i.e. diaphragmatic
In crocs, the 2 heads of the /m. diaphragmaticus/ insert
(originate?) on the anterolateral surface of the pubis. According to Ruben,
non-avian theropods, especially those with a typical saurischian pubis with
a distal thickening, must have had the same lung anatomy.
Birds, on the other hand, developed their air sacs (esp. the large
posterior sac) late in their evolution, as evidenced by the uncinate
processes, enlarged sternum, and loss of gastralia (in Ornithothoraces?
sorry, no papers handy, but at least excluding Enantiornithes according to
Ruben) that other theropods lack. Those features are apparently correlated
with the flexibility of the ribcage / expansion of the air sacs.
Ruben's case is that no non-avian theropod has a fully retroverted
pubis without an anterior prong or other distal thickening like
_Archaeopteryx_ has. I showed him _Compsognathus_, which lacks much of an
anterior prong, and he still thought it was enough for the /m.
diaphragmaticus/ attachment. Ceratosaurs? Still distally thickened, at
least most of 'em.
Ahh, but maniraptorans? I couldn't find any nice pics of
dromaeosaur pubes, but I'm pretty sure at least _Adasaurus_, and probably
_Velociraptor_, has a pubis basically identical to that of _Archaeopteryx_
(except size). Does anyone know of a non-avian theropod with a fully
retroverted pubis and no vestige of an anterior boot? (I acknowledge that
the exact anatomy of the pubis of _Archaeopteryx_ is disputable).
I also mentioned _Mononykus_; Ruben was unsure of that guy's lungs.
Ditto for ornithischians, therizinosauroids. I heard somewhere that there's
a dromaeosaur with possible uncinate processes. Other ideas?
I find his argument interesting; skeletal correlates of soft tissue
anatomy are a pet interest of mine, but I think the may be quite wrong at
least on the dromaeosaur end. Calling all distal pubis / lung morphology
John R. Hutchinson
Department of Integrative Biology
3060 Valley Life Sciences Bldg.
University of California - Berkeley
Berkeley, CA 94720 - 3140
Phone: (510) 643-2109
Fax: (510) 642-1822