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Berman, Sumida and Lombard (1992) suggested that
diadectomorphs share a more common ancestor with pelycosauria than other taxa
like captorhinomorphs; pointing out the fact that the parietal lappet of
tseajaia contrasts with the postorbital-supratemporal conjuction of the other
diadectomorphs and pelycosaurs, the authors proposed as primitive condition the
parietal lappet of tseajaia and as derived one the postorbital-supratemporal
conjuction of the
others.
So I would ask:
1) captorhinomorphs and tseajaiids have a parietal
lappet that reaches the squamose, the other diadectomorphs, the
pelycosaurs and the millerettids no, if diadectomorphs are amniote (Lee and
Spencer 1997) is it possible that the separation between the ancestors of
pelycosaurs and millerettids from one side and of captorhinomorphs and
protorothyridids from the other occur already at this level?
Or we have to consider the parietal lappet of
protorothyridids and captorhinomorphs a secondary reverse to a primitive
state?
2) As far as i know the great majority of
labyrinthodonts that lost the intertemporal, show postorbital-supratemporal
conjuction instead of the parietal lappet of tseajaia; if this condition and not
the parietal lappet is the more primitive the reduction of supratemporal in
protorothyridids and captorhinomorphs is a secondary reverse to a primitive
state that occur in an anapsid skull or is it possible that this reduction is
due to a develop of an upper temporal fenestra subsequently closed by a lateral
process of parietal? In other words is it possible that paleothyris had an
ancestor with an araeoscelis-like cheek that closed the upper fenestra enlarging
the parietal?
3) Reisz (1984) support the diapsid origin of
araeoscelis cheek on the following:
I) triradiate configuration of postorbital and
jugal
II) posteroventral edge of the postorbital
smooth and concave
III) posterior and dorsal processes of the jugal
separated by
a smooth concave
notch.
IV) the area between the posterior margin of the
jugal and
postorbital normally
occupied by the lower temporal
fenestra covered by
squamose.
V) an anteroventral extension of the
squamosal overlaps the
lateral surface of the posterior
process of jugal.
All the above arguments seems to me to be
approximately valid also for paleothyris, is it possible that the anapsid
condition of paleothyris is derived from a diapsid ancestor?
Sorry for the long letter, thank you in advance for
your answers.
Alberto Arisi - Italy
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