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Re: dino dna
>Rob Myerson writes:
>>This I can live with. Very exciting! (But PREDATING a dino-mammal split?
>>Needs more data.)
>Would you explain this "dino-mammal" part. I thought that dinosaurs
>evolved from a separate group than mammals.
Mammals presumeably arose during the Triassic from mammal like reptiles, of
which little is known. There are few if any Triassic fossils which can be
identified as mammals. Mammals appear suddenly in the Jurassis, but who know
what ancestors led to this Jurassic radiation. It has been suggested(Romer,
Vert. Paleon.) that Synapsids led to mammals. During those mysterious
Triassic days, along with the mammal-like reptiles, theropod like dinosaurs
appeared. The Archosauria probably gave rise to lines leading 1) to
mammals, 2) to dinosaurs, 3) to modern day reptiles, and, as I suggested 4)
to a line culminating in modern day birds. Where and exactly when these
branches appeared from the arcosaurian stem, remains to be elucidated.
Correct me if I am wrong, but I can find no trees that don't have dotted
lines during the Triassic, that is, back then, it's just speculation. If
there are recent fossil discoveries that further resolve this issue, please,
please let me know. My analysis of the sequence data, so far, sheds some
light on the branching points in the early to middle triassic, and it is
here that the birds branch off separately from the dinos and mammals. I am
estimating the 40 MYA, and that estimate will be fine tuned when, and if
(that's a big if), I get more data.
PS- I have been getting some queries about the usefulness of genetic data
vs. morphological data. Let me just say that genetic data produces a gene
tree, and reflects evolution in genes, independent of morphology.
Morphological characteristics are not connected with genetic change in the
way most people think. The genes I look at evolve independently of
morphological characteristics and a physiological genes. Since
Physiological genes account for over 98% of any organisms' genome, and
pattern genes(morphological genes) represent only 1 to 2% of the genome, you
can see where the most useful information can be gained.(More on this later).