No more paedomorphosis

[Dinogeorge <Dinogeorge@aol.com>]

In a message dated 98-04-14 22:39:55 EDT, m_troutman@hotmail.com writes:

<< I don't see how Rahona is a dromaeosauris. Yes, it is 
 dromaeosaur-like, but it is different in some features:
 
 1) The proximodorsal ischial processes.
 2) Completely reversed hallux. 
 
      Now since dromaeosaurs lack these two important features, it is 
 unlikely that Rahona was a dromaeosaur.  >>

As you know, I consider the hallux reversed in practically all theropods. It
articulates loosely at the back of the second metatarsal and was probably as
laterally mobile in life as the human thumb--which can align parallel with the
other digits or oppose them. So this character is not absent in
dromaeosaurids, but is secondarily modified so that the reversed hallux was
kept off the ground during walking or running (a cursorial adaptation).

The other character is probably taxonomically ambiguous. Perhaps you could be
a bit more specific? Tell me, for example, how presence or absence of one
character would exclude a species from a particular family, if it possesses
numerous other characters of that family.

_Rahonavis_ is a dromaeosaur[oid]--not in the family Dromaeosauridae, which
would include mainly the secondarily flightless, cursorial forms, but in an
unnamed sister-group family of its own, that could presumably include the
numerous other flying dromaeosaur[oids] as yet undiscovered. And most
definitely in the more inclusive group Deinonychosauria.

The _Rahonavis_ specimen gives me the idea that the enlarged claw on the
second digit of dromaeosaurids and other theropods might have been the most
specifically opposed ungual to the retroverted hallux, so that perching was
accomplished in these forms primarily by the claws of digits 1 and 2. In the
ground-dwelling descendants, digit 1 shrank, but digit 2 was exapted into the
celebrated weapon.