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Re: Archosaur Origins...was:MESENOSAURUS ERRATA.
In a message dated 8/25/01 3:29:12 PM EST, ELurio writes:
<< Why should we? We're talking PERMIAN here, when all archeosaurs were one
(Archosaurus), and we don't have any evidence for fiberous integument in any
lepidosaurs or turtles in either the fossil record or living species. From
all the reading that I remember, Archosaurus only had minor differences from
the lepidosaurs of the time. >>
No, you are misinformed. Archosaurus is quite different from lepidosaurs, and
what there is of it is very similar to Proterosuchus from the Early Triassic.
It would be difficult to mistake Archosaurus for any lepidosaur (or
prolacertiform). The existence of a proterosuchian as early as the Late
Permian indicates the existence of less derived archosaurs in earlier times:
Where there is a specimen, there is a population; where there is a
population, there is a species; where there is a species, there is a lineage.
With regard to integument, I was referring to that of possible >arboreal
prolacertiforms<. If pterosaurs are prolacertiform descendants, then it is
quite possible that some prolacertiforms already had the kind of hairlike
"pelage" that is well known in pterosaurs. This may, in turn, have also
appeared other prolaceriforms, such as those from which those animals widely
known as archosaurs evolved, and it may have been preserved in the arboreal
lineages that led to birds and dinosaurs. Secondary loss of hairlike
"pelage," or conversion to smooth scutes, might be expected in aquatic
reptiles such as proterosuchians, so absence of hairlike "pelage" in these
groups does not preclude its existence in ancestral prolacertiforms.