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Thomas R.Holtz, 13.Dec.1995 in "Synapsids are
not reptiles" wrote:
Reptilia is defined as the most recent ancestor
of
turtles, lepidosaurs and archosaurs. Uricotely,
enhanced color acuity, reptilian scales and so forth were probably never present
in Dimetrodon.
There is the possibility that turtles are diapsids
themselves (Rieppel & de Braga), in that case we cannot be sure of the
uricotely and enhanced color acuity of the basal reptiles, because Reptilia, in
the Gauthier study, includes near diapsids also captorhinidae, and for them we
have no evidence.
The first amniotes were very different from the
actual lissamphibians, they were probably not arboreal, not fossorial, not
small, not skinbreathers with reduct rib cage,
they have not a bimodal aquatic-terrestrial life
with consequent fluid permeable skin. A big fully terrestrial amniote like
Dimetrodon needs skin protection against trauma, considering also the sprawling
position of the limbs that maintains the body so near the ground. The
keratinized
scales are not an improbable protection
against trauma in first amniotes, because fur and feathers are too much derived.
(the study of L.M. Frolich is enlightening on this argument)
Thomas R. Holtz, 13. Dec. 1995 wrote:
Synapsida is mammals and all taxa closer to mammals
than to reptiles.
Sauropsida is reptiles and all taxa closer to
reptiles than to mammals .
There is a strong possibility that diadectomorphs
are amniotes (Lee & Spencer), in that case where we have to place them in
sauropsida or synapsida?
The situation in amniote phylogeny is so fluid that
perhaps is better, at least for the moment, to maintain in use the traditional
distinction: synapsida-diapsida-anapsida, all inside the Reptilia.
Alberto Arisi
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