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Re: Feduccia ORIGIN



At 12:23 PM 1/10/97 -0500, Caitlin Kiernan wrote:

>swf@ElSegundoCA.NCR.COM wrote:
>
>>He [Feduccia] seems to be ignoring the possibility of a long-forelimbed,
>>arboreal *dinosaur*.
>
>>Long-forelimbed we have, and in forms apparently close to the ancestry of
>>birds.  We call them deinonychids.  Other, slightly more distant, examples
>>include troodontids and ornithomimids. 
>
>All of these groups are Cretaceous.

All the GOOD specimens of these groups are Cretaceous.  So what?  Troodontid
teeth (or something very much like them) are known from the Morrison (Late
Jurassic), and teeth resembling those of dromaeosaurids and troodontids are
known as far back as the Middle Jurassic in Great Britain.  These are
published, documented materials which Feduccia and his supporters refuse to
acknowledge.

This says nothing about the two fundamental problems with Feduccia's studies:
I) Lack of a fossil in a stratum does not mean lack of a member of that
taxon in that age.  A couple of years ago, there were no known ornithomimids
before the Aptian/Albian, and no known tyrannosaurids from before the
Senonian.  Now both are documented in the Barremian.

II) If known presence of an ancestral taxon older than the group in question
is required, than Feduccia must accept that chimps and gorillas evolved from
humans, that scyphozoan jellyfish evolved from anthozoan corals, that
gnathostome vertebrates must have evolved from conodonts, and other unlikely
events.  Because of taphonomic biases of environment, preservablity, and
rarity, some taxa within a clade have a better fossil record than their
relatives.  Just because one member of the group has a better chance of
being preserved in the fossil record than the other does not mean it was
ancestral to the other.

>I think that Feduccia is concerned with finding a suitable dinosaur ancestor
>predating (or at least of roughly the same age) as the earliest known birds
>(and he seems to lean toward the possibility that this may be _Protoavis_,
>and since the Jurassic birds are so advanced, that means he's calling for an
>ancestor in the Carnian or earlier).  He judges neither _Eoraptor_ or
>_Herrerasaurus_ viable candidates (short-limbed, cursorials).

Actually, I think Eoraptor and Herrerasaurus make good viable morphological
candidates for the ancestry of birds (and tyrannosaurs, and allosaurs, and
abelisaurs, and possibly even dicraeosaurids, stegosaurids, and
centrosaurines...) although they occur somewhat too late in the fossil
record to be direct ancestors.

>I'm going to go back over Feduccia's discussion of the morphologic problems
>he perceives with a theropod ancestry for birds this weekend, and maybe I'll
>wade into this a little more deeply.

Just remember: the furcula has now been found in allosaurids,
tyrannosaurids, and dromaeosaurids, so its distribution among theropods is
greater than was known when he wrote the text.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661

"To trace that life in its manifold changes through past ages to the present
is a ... difficult task, but one from which modern science does not shrink.
In this wide field, every earnest effort will meet with some degree of
success; every year will add new and important facts; and every generation
will bring to light some law, in accordance with which ancient life has been
changed into life as we see it around us to-day."
        --O.C. Marsh, Vice Presidential Address, AAAS, August 30, 1877