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Re: Terrestriality is a bias



 

    Tracy Ford wrote:

>There is a preconceived notion on what an early bird would look like. But when one is found in the Late Triassic it is considered to be a composite because it doesn?t fit that preconceived notion. I?ve talked to Sanker and the person who excavated _Protavis_. I believe them that it is just one genus in the block. I bet even if a totally intact, articulated specimen, it will still be thought of as a composite animal.
Interested parties are directed to view a two page spread of the remains on pp. 44-45 in :

Steele, Bill, "Ruffled Feathers," _Discover_, May 1992.

Compare with Chatterjee's illustrations (sans photos) in _The Rise of Birds_.

Decide for yourselves whether the reconstructions are accurate and the claims of the avian nature of the specimen justified.  At the risk of stating the obvious, I think that the bones would be much more useful if there were more of them and they were in better condition (as in Tracy's bet, above).

>The opposite is true for _Rahonavis_. It is a long tailed bird that is older than Archaeopteryx.

Dated to 65-70 million years before present, this is not correct.  It combines features of early birds and dromeosaurs, but its late appearance suggests that it is a throwback rather than an early bird itself.  But I know that you knew that.

Regarding the physical difficulties of getting dromaeosaurs up a tree, this is less problematical in the recently described smaller forms, such as _Bambiraptor_ and the eagle-sized _Sinornithosaurus_.  Even smaller species may well have existed, and not been preserved, particularly if their habitat was a tropical forest, and immature dromaeosaurs would surely have been "small enough" to have jumped around in the trees if they had wanted to, long arms, retroverted pubes, cat-like claws and all.  And the pivotal theropod ancestor of the birds need not have been a dromaeosaur per se, but rather the most recent common ancestor of both dromaeosaurs and early birds (such as _Archaeopteryx_).

Regarding the question of arboreal dromaeosaurs, perhaps we'll have to wait until a preserved dromaeosaur nest is found in a fossilized tree to nail this one down!  (All right, George, I know you can't speak of this until the paper comes out (joke))!

-- Ralph W. Miller III      gbabcock@best.com

Question:  Is "dromaeosaur" or "deinonychosaur" the preferred term, or are they not synonymous?