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

Are Alvarezsaurs Birds? (was Re: Details on Eoenantiornis)



----- Original Message -----
Sent: Thursday, December 21, 2000 3:46 AM
Subject: Re: Details on Eoenantiornis

David Marjanovic wrote-
 
I've just got the Nature paper. Microraptor has distally placed and long halluces (both more so than in Archaeopteryx), but they are definitely not reversed. Of course, I can't judge whether it may have been revers*ible*, and preservation is another issue...
 
My statement was based on the coding of this character in Xu et al.'s data matrix.
Hm... there seem to have happened a few blunders in this matrix (I just got access to the Supplementary Information). For example, character 28 (shape of fused clavicles: absent (0), greater than 90° (1), less than 90° (2) was coded as 0 in Allosaurus. Maybe there is a typo somewhere.
BTW, what arguments are there to exclude alvarezsaurids from birds? The prokinetic skull of Shuvuuia seems clearly avian to me.
They just never fall out as avians (Archaeopteryx + Neornithes) in any of my cladograms (or the AMNH team's recent ones, Sereno's, etc.).  Alvarezsaurids have various primitive characteristics like short coracoids, scapulae without triangular anteriorly projecting acromions, ventrally directed glenoids and the lack of a proximodorsal ischial process that combine with the more birdlike characters of some dromaeosaurs to place them below Aves.  At most, sometimes they're the sister group to Aves, but my most recent phylogenies (with Microraptor added) place dromaeosaurs above them and troodontids (which are the [next] outgroup to Aves if alvarezsaurs are closest).  Sure, they also have a ton of bird-like characters, but that's just how the current cladograms crumble.
The primitive characteristics in the shoulders of alvarezsaurids could be related to secondary flightlessness (still no-one has a good idea what their arms were good for?). The scapula and coracoid of Gastornis (aka Diatryma) look like those of a troodontid, e. g. Sinornithoides. I can't say anything about that ischial process.
 
Both alvarezsaurs and (basal) oviraptorosaurs (and segnosaurs?) have quite short, flexible tails; if oviraptorosaurs are closely related to pygostylians... more in my forthcoming article :.-( .