=Thrausmosaurus serratidens= new genus and new species
(_Thrausmosaurus_ is formed from the neuter Greek noun, _thrausma_,
meaning fragment, and the masculine Greek noun, _sauros_, meaning
reptile. The specific name, _serratidens_, is formed from the Latin
_serratus_, meaning serrate, and the masculine Latin noun, _dens_,
meaning tooth. The specific name is used as a substantive in apposition
with the generic name.)
_Type specimen._--Fragmentary left dentary, bearing five teeth, the
most posterior of which is broken at the base, KU 11120.
_Referred specimens._--Fragmentary ?left maxilla, having two teeth, KU
11121; fragmentary left dentary having two teeth, KU 11122.
_Horizon and locality._--From the early Permian fissure deposits in the
Arbuckle limestone of the Dolese Brothers Limestone Quarry,
approximately 6 miles north of Fort Sill, in sec. 31, T. 4N, R. 11 W,
Comanche County, Oklahoma.
_Diagnosis._--Small; teeth thecodont, compressed laterally, recurved
distally, and bearing anterior and posterior cutting edges; anterior
serrations limited to recurved portions of teeth, posterior serrations
extending nearly entire length of teeth; lateral compression of teeth
more pronounced medially than laterally; bases of teeth expanded.
_Description._--The type specimen is 16 mm. long. It bears five teeth
that are implanted in a straight row. Empty sockets are present between
the first and second teeth, and the third and fourth teeth. The first
tooth is 3.0 mm. long, the middle two are each 2.5 mm. long, and the
fourth tooth is 2.0 mm. long. The fifth tooth is broken off at its base.
The empty sockets are large. The mouth of each is circular and
approximately 2.0 mm. in diameter. Both sockets are 1.25 mm. deep. The
bases of the teeth are expanded to fill the sockets, although the blades
of the teeth arise from only the lateral portions of the bases. The edge
of the dentary rises above the bases of the teeth medially, thereby
producing a small depression at the junction of each base with the
dentary bone.
The lateral compression of the teeth is pronounced but asymmetrical, in
that the lateral surface of each blade is more convex than the medial
surface.
[Illustration: FIGURES 4-6. _Thrausmosaurus serratidens_, lower Permian,
6 miles north of Fort Sill, Comanche County, Oklahoma. All x 3.
FIG. 4. KU 11120 (type specimen), lateral view of left dentary.
FIG. 5. KU 11121, lateral view of ?left maxilla.
FIG. 6. KU 11122, lateral view of left dentary.]
The recurvature of the anterior cutting edges is much more severe than
that of the posterior edges, but the recurvature of both is limited to
the distal half of each tooth.
The serrations of the cutting edges are not visible to the naked eye and
are limited on the anterior edges of the teeth to those portions of the
blades that are recurved. The posterior serrations extend nearly to the
junction of the blade of each tooth with its base. The serrations tend
to be more nearly crenulate than cuspidate.
A portion of the lateral wall of the dentary surrounding the Meckelian
canal is present. The external surface of the wall is gently convex and
smooth, without sculpturing. The internal surfaces of the canal are
unmarked either by muscle scars or foramina.
The fragment is a piece from the posterior portion of the dentary, since
the decrease in height from the first tooth to the fourth is pronounced.
KU 11122, a fragment of the left dentary bearing two teeth, is 7.5 mm.
long. The anterior tooth is 3.0 mm. long; the posterior tooth is 3.5 mm.
long. The shape of the teeth and their implantation conform to the
description of the type specimen. The lateral surface of the fragment is
smooth and gently convex. What little is present of the surface
bordering the Meckelian canal is unmarked.
The ?maxillary fragment bears two teeth which are 3.0 mm. long, and
which conform in their characters to the type. The lateral, medial and
ventral surfaces of the fragment have been sheared off, so that an exact
identification of the bone is impossible. Presumably the fragment is too
deep dorsoventrally to be a piece of the dentary, and no sign of the
Meckelian canal is present.
_Discussion._--The implantation, lateral compression, recurvature and
cutting edges of the teeth borne by these fragments make clear their
sphenacodontid nature. The characters of the fragments are too few to
determine subfamilial affinities, however. That the fragments are the
remains of adult animals can be only surmised from the lack of bones or
teeth of large pelycosaurs in the extensive collections of the
University of Kansas from the Fort Sill locality.
If _Thrausmosaurus_ is, in fact, adult, the genus is an unusually small
sphenacodontid, and of significance both on that account and because of
the resemblance of the teeth presently known to those of its far larger
relatives.
_The Fort Sill Locality._--Peabody (1961) suggested that the fissures of
Fort Sill had been used as dens by predatory animals in the early
Permian, and that the unusually abundant bones in the fissures were the
remains of animals eaten there by these occupants. Evidence now known to
me affords an alternative explanation that is presented here as a
preliminary to a more complete study of the fauna and paleoecology of
these deposits currently being undertaken.
The suggestion that the skeletal material found in the fissures is the
remnant of the prey of other animals is questionable because of: