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Re: climbing dromaeosaurs and friends



In a message dated 12/7/00 11:08:00 PM EST, Dinogeorge@aol.com writes:

<< In a message dated 12/7/00 10:38:05 PM EST, scott_hartman@hotmail.com 
writes:
 
 << Which certatosaurs are you refering to?  Certainly well reserved Ghost 
  Ranch Coelophysis didn't have a retroverted hallux. >>
 
 It certainly does. Take another look. But it's not quite as distal as in 
 later theropods and birds, but as in all cursorial theropods it is reduced 
 (secondarily). In cursorial theropods (and in phorusrachids and in extant 
 ratite birds, too) a truly retroverted hallux is an impediment to running, 
so 
 it quickly reduces to a loosely articulating, nearly vestigial digit. >>

Let me modify my original answer just a bit. In C. bauri the first metatarsal 
is detached from the tarsus and articulates with the second metatarsal along 
a medial groove. It is rather long and slender, unlike the more advanced 
retroverted halluces of more derived theropods. But the form of the 
articulation allows the first metatarsal and its digit considerable axial 
rotational mobility, so that the first digit could align either with the 
other digits or opposed to them. This suggests to me that the retroverted 
hallux in coelophysids is caught in transition from its original position (as 
seen in herrerasaurians and lagosuchians) to the more distal, more strongly 
reversed position of the more derived theropods. The late Sam Welles once 
confided to Tracy Ford and me his opinion that the hands of Dilophosaurus and 
other ceratosaurs were built for grasping, with opposable polluces. I believe 
he was quite correct, and when you consider that they also probably had 
grasping feet, with digit I opposable to the other digits, it is not a big 
stretch to envision the common ancestor of birds and ceratosaurians as a 
small, prehensile tree-dwelling climber--maybe it resembled some of the 
reconstructions of Protoavis I've seen. Although it probably had feathered 
wings, I doubt it could have used them for powered flight at that stage of 
avian evolution. They were likely more useful in short arboreal glides or in 
parachuting during accidental falls. The hands of ceratosaurs still had four 
not particularly long fingers and seem better adapted to grasping rather than 
to powered flight.