Dinogeorge Digest #4

[Dinogeorge@aol.com]

I've received several favorable e-mails on converting my posts into a daily
digest, so I'll keep doing this for a while.

Subj:   Re: Brooding feathers, Chinese dinobirds
Date:   98-06-28 01:46:20 EDT
From:   Dinogeorge
To:     jhecht@world.std.com, TomHopp

In a message dated 98-06-27 21:21:36 EDT, jhecht@world.std.com
writes:

<< Could all those Confuciusornis be the equivalent of the assorted sparrows,
swallows, woodpeckers and robins flying around a modern lake -- but not yet
 differentiated because no one has studied enough of them as carefully as
 Ji, Currie, and Norell did Protarchaeopteryx and Caudipteryx (which they
 originally thought was just another Protarchaeopteryx). >>

The situation might be more like that of gulls here in southern California,
where there are a number of similar but different species that could well be
mistaken for one another were only their squashed skeletons available for
study. They all live pretty much sympatrically and are distinguished almost
exclusively by various patterns of coloration.

Subj:   Re: Back-evolution of limbs.
Date:   98-06-28 01:46:11 EDT
From:   Dinogeorge
To:     jbois@umd5.umd.edu

In a message dated 98-06-27 21:01:33 EDT, jbois@umd5.umd.edu
writes:

<< I don't know whether the following has been discussed before, but:
 
 Why is it that birds--and only flying birds at that--are the only
 creatures to return to their former mode of locomotion, i.e., they may
 become secondarily flightless. >>

This is surely a consequence of the fact that in birds, hindlimb locomotion
became decoupled from forelimb locomotion (at about the same time that
lagosuchians and other such small, slender-limbed bipeds appear in the fossil
record--back in the Middle to Late Triassic). Their >most< former mode of
locomotion, however, was quadrupedal, and flightless birds never reverse this
far.

<<Perhaps there is a unidirectionality to limb evolution.>>

This is often called Dollo's Law: once a body part is lost (or severely
atrophied) through evolution, it does not return, and if necessary a
different body part may become exapted for the purpose the original body part
once served. The unidirectionality of this process results from the same
physical process that makes it easy to shatter an egg but very, very
difficult to reassemble it (all the king's horses...).

Subj:   Re: Tails from Liaoning
Date:   98-06-27 15:54:08 EDT
From:   Dinogeorge
To:     tkeese1@gl.umbc.edu

In a message dated 98-06-27 14:09:07 EDT, tkeese1@gl.umbc.edu
writes:

<< Anyway, while sketching the fossils there (one _Protarchaeopteryx_, two
 _Caudipteryx_, two _Sinosauropteryx_, and two _Confuciusornis_), I noticed
 that _Protarchaeopteryx_ seems to have a tail fan very similar to that of
 _Caudipteryx_. Are my eyes fooling me here, or is this some kind of
 convergent(?) structure? There also appears to be a miniature version of
 this on the adult _Sinosauropteryx_ (the one that's supposed to have a
 mammal jaw in its gut, although my untrained eyes could not find it). >>

As I noted back in the first printing of Mesozoic Meanderings #2 (1991), the
first airfoil developed by birds was probably the feathered tail, which
literally has to do nothing but be there to have some aerodynamic function,
such as providing stability and directionality to arboreal leaps. The
feathered tail would also have a probably colorful display function, of
course (and which came first--display or aerodynamic--is very moot). In
ground-dwelling descendent theropods, the aerodynamic function pretty much
vanishes, but the display function would certainly remain. So I wouldn't be
at all surprised to find display tail feathers of all kinds on a wide variety
of small theropods throughout the Mesozoic. Probably there were numerous
instances in which sister species could have been distinguished only by
differing tail-feather (and other such) patterns.

I first came across this concept in the various papers on _Cosesaurus_, whose
putative feather impressions occur mainly along the tail. Also, decades ago
at Don Glut's house I saw a little cast bronze sculpture of a dromaeosaurid
(say, _Deinonychus_) with a very decorative and appropriate fringe of
horizontal feathers running along the tail. Anyone else ever see this
sculpture?