View/Open - American Museum of Natural History

19301
Romer, The Pennsylvanian T'etrapods of Linton, Ohio
123
ridge curving in medially behind these openings. The ectopterygoid is somewhat
narrower, but of considerable length. There is no trace of an extra postectopterygoid
element, which Watson has suggested might have been present in Orthosaurus.
On the left side there appears to be a brace extending inward from the lower margin
of the jugal to strengthen the posterior margin of the ectopterygoid and the pterygoid
at the edge of the fenestra for the temporal muscles. On this side the pterygoid
is disarticulated posteriorly. This last element is very large and broad anteriorly,
and, although a median suture between the two sides is seen for only a short distance,
the interpterygoid vacuities were obviously very small. The surface of the palatal
ramus is thickly studded with fine teeth. Most of the quadrate ramus is seen, somewhat
displaced, on the left side. The process articulating with the braincase is not
clearly visible in the ventral view, but this may be seen from above in a break through
the roof of the skull in the parietal region.
The braincase appears to have been lost before burial, as the under surface of the
table, as far as visible, shows no traces of it.
The ventral surface of the larger specimen gives some information which supplements
that derived from the smaller. This palate is poorly preserved, much broken
and badly pyritized, while the sides of the skull have been doubled under on both
sides, rendering only the central portion visible at all. Part of the pterygoids are
visible anteriorly, thickly studded with small teeth. Somewhat more posteriorly they
appear to have been badly broken, but the region lateral to the braincase is seenton
both sides. A comparatively thin articular process extending dorsally and medially
may be made out. On the left side there are obscure traces of a very tall paraotic
flange passing from the pterygoid dorsally above the braincase.
Anteriorly the cutriform process of the parasphenoid may be seen dorsal to the
pterygoids. It is broad in this region (beneath the frontals) and narrows rapidly
as it passes backward. Most of the braincase is preserved, although crushed dorsoventrally
and not in a very good condition. The basipterygoid process is large and
quite thick, facing anteriorly and somewhat ventrally. Behind this there is a lateral
expansion into the otic region, the surface rising towards the table of the skull laterally.
A depression appears to represent the fenestra ovale. The posterior boundary of the
parasphenoid (? or basisphenoid) may be traced across the ventral surface. Curved
ridges represent the tubera basisphenoidales. The condyle is of primitive type, a
single subcircular cavity, mainly formed by the basioccipital, but with the exoccipitals
entering into the dorso-lateral parts. The lower jaw is represented by two nearly
complete rami in the small specimen, and fragments of both sides in the larger form.
The inner surface is unfortunately not exposed in any case. The outer surface is of
the primitive character and needs no comment. A lateral line canal is visible along
the entire length of the lower margin.
The teeth are all grooved at their bases, smooth in approximately the upper twofifths.
The basal portions are cylindrical; distally they are somewhat compressed,
with some development of a cutting edge anteriorly and posteriorly, much as in
Embleton and Atthey's description of "Loxomma." However, there is some tendency
generally towards a backward curvature of the tips, especially noticeable in the large
anterior dentary teeth.
The skull reconstruction, illustrated, is based mainly on the more
complete small specimen. It is unfortunate that the posterior portion