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Re: dino dna
>Genetic material from extinct organisms may not be as difficult to obtain as
>you might think. I have been successful in obtaining gene fragments from
>110 MY Tenontosaurus, and 68 MY Ornithomimus, and Deinonychus, and probably
>T. rex, although I have not sequenced that yet to confirm dino origin. You
>are right in the fact that DNA must come from fossil sources, and therefor
>is limited by the availability of the fossils. The older the fossil, the
>less chance of getting intact DNA frags large enough to supply enough data
>for analysis. However, the resulting data will either back up the
>morphological identification and stratigraphic placement of the age of the
>fossil, or will contradict it, or any degree in between. This is where the
>genetic data may override the morphological data. So far, my data shows that
>dinos and mammals shared a commmon ancestor approx. 230 MYA, but what
>happened in between has yet to be seen.
Conviently, that is the date of the oldest mammals and dinosaurs. I think
you are probably seeing homoplasy, since vast amounts of anatomical data
reject a dinosaur-mammal union (see Gauthier et al. 1988 for a review of the
skeletal and soft-tissue data).
Also, there are taxa clearly closely related to mammals going back to the
Permian, while close relatives of dinosaurs (excluded from that clade only
becuase they lie outside Saurischia+Ornithischia, but are otherwise closer to
dinos than to pterosaurs) in the Middle Triassic). It would seem
unreasonable that broken fragments of uncertain origin from the Cretaceous
could overturn morphological hypotheses based on good specimens from the
Triassic and older.
There is a myth that trees derived from genes or other biomolecules are more
"real" than are morophological trees. However, any review of the relevant
data of extant mammal groups (for example) shows that, currently, about
every possible combination of taxa is supported for different parts of the
genome (recent reviews by McKenna, as well as others). In other words, there
is at least as bad, if not worse, resolution of phylogeny from molecular
techniques as there is from morphology.
Thomas R. Holtz, Jr.
Dept. of Geology
University of Maryland
College Park, MD 20742