=Delorhynchus priscus= new genus and new species
(_delos_, Gr., evident; _rhynchos_, Gr., neuter, nostril; _priscus_, L.,
ancient. _Delorhynchus_ is masculine because of the ending that it
acquires when transliterated into Latin.)
_Type specimen._--Fragmentary left maxilla, bearing four teeth, KU
11117.
_Referred specimens._--Fragmentary right maxilla having four teeth, KU
11118; fragmentary left maxilla having four teeth, the most posterior of
which has been broken, KU 11119.
_Horizon and locality._--A fissure deposit in the Arbuckle limestone at
the Dolese Brothers Limestone Quarry, approximately six miles north of
Fort Sill, in sec. 31, T. 4 N, R. 11 W, Comanche County, Oklahoma. These
sediments are of early Permian age, possibly equivalent to the Arroyo
formation, Lower Clear Fork Group of Texas (Vaughn, 1958: 981).
_Diagnosis._--Small; marginal teeth conical, slender and recurved at
tips; marginal tooth-row without caniniform enlargement; narial opening
enlarged and bordered dorsally, posteriorly and ventrally by maxilla;
maxilla with foramen opening laterally at posteroventral corner of
naris.
_Description_ (based on 3 maxillary fragments, see Table 1).--Each of
the maxillary fragments bears four thecodont teeth. These are conical,
slender and sharply pointed; in their distal third they are slightly
recurved, laterally compressed, and have anterior and posterior
non-serrated cutting edges. In medial aspect at their bases, the teeth
are longitudinally striated. The bases of the teeth are circular in
cross-section and are slightly bulbous. There is no caniniform
enlargement of any of the teeth, the longest tooth of each fragment
being differently placed in the series of teeth and little longer than
the others. There is no swelling on either the internal or external
surfaces of the maxillae. The teeth are in a continuous series; no
diastema or maxillary step is evident.
[Illustration: FIGURES 1-3. _Delorhynchus priscus_, lower Permian, 6
miles north of Fort Sill, Comanche County, Oklahoma. All x 3.
FIG. 1. KU 11117 (type specimen), lateral view of left maxilla.
FIG. 2. KU 11118, lateral view of right maxilla.
FIG. 3. KU 11119, lateral view of left maxilla.]
The fragments have been broken along similar lines of fracture, and each
is approximately rhomboidal in shape. The maxilla encircles the
posterior border of the naris and extends dorsally above the naris to an
extent sufficient to indicate the probable exclusion of the lacrimal
bone from the narial border. At the posteroventral corner of the naris a
foramen opens onto the lateral surface of the maxilla. The opening is
the entrance to a canal that runs posteriorly above the tooth-row
throughout the length of each specimen. Beneath the naris the maxilla
extends as a broad tapering shelf, the ventral surface of which
articulates with the premaxilla. The narial rim is wide, but wider
ventrally than dorsally. The plane of the narial rim is oblique to the
lateral surface of the maxilla. The external surface of each fragment is
grooved and pitted. The ossification of each fragment appears to have
been complete.
TABLE 1.--DIMENSIONS, IN MILLIMETERS, OF THREE MAXILLARY FRAGMENTS OF
DELORHYNCHUS PRISCUS
Key:
A. Anterior height of fragment
B. Posterior height of fragment
C. Length of fragment at tooth-row
D. Dorsal length of fragment
E. Mean length of teeth
F. Anterior width of naris
============================================================
CATALOGUE NUMBER | A. | B. | C. | D. | E. | F.
AND MEAN | | | | | |
-----------------+------+------+------+------+------+------
KU 11117 | 6.0 | 8.0 | 6.0 | 8.0 | 3.0 | 3.0
KU 11118 | 6.0 | 6.0 | 9.0 | 8.0 | 2.0 | 3.0
KU 11119 | 6.6 | 8.0 | 10.0 | 11.0 | ? | 4.6
-----------------+------+------+------+------+------+------
Mean | 6.2 | 7.3 | 8.3 | 9.0 | 2.5 | 4.5
-----------------+------+------+------+------+------+------
_Discussion._--The Nitosauridae are small primitive edaphosaurs with a
moderately elongate face, sharp subisodont teeth, little development of
canines and few specializations. The jaw is of a primitive type and
articulates on a level with the tooth-row. The palatal dentition is
primitive (Romer, 1956:280). The nitosaurids are thought to be related
to the later Caseidae, and the most obvious structural similarities are
found in the postcranial skeleton (Vaughn, 1958:989). Cranial
resemblances between the families are fewer, but nevertheless indicate
that a nitosaurid-caseid relationship exists.
Vaughn (1958) described a small pelycosaur, _Colobomycter pholeter_
(Eothyrididae, Ophiacodontia) that structurally resembles the Caseidae.
This individual also was obtained from the Fort Sill locality. In
Vaughn's opinion the features of _Colobomycter_ indicate a close
relationship between eothyridids and caseids and the possibility that
the caseids may well have been of eothyridid rather than nitosaurid
derivation.
In view of this historical uncertainty of the relationships between the
Nitosauridae, the Eothyrididae and the Caseidae, it is well to consider
how the maxillary fragments described above differ from and resemble
representatives of each of these three families as reported in the
literature.
_Delorhynchus_ resembles _Colobomycter_ in size. The mean
extra-maxillary length of the undamaged teeth of the three fragments is
2.5 mm., equal to that reported by Vaughn (1958:985) for teeth about
midway in the postcanine series of _Colobomycter_. None of the teeth of
_Delorhynchus_ extends beyond the maxillary rim as far as does the
canine of _Colobomycter_ (3.5 mm.).
The teeth in both genera are conical and sharply pointed. The naris in
each is enlarged, and the lacrimal is excluded from the narial margin in
each (by inference in _Delorhynchus_.)
The differences between the maxillae of _Colobomycter_ and
_Delorhynchus_ are most striking in the lack of canines in the latter
and the correlated absence of modifications of the maxillary for support
of canines. Additionally, _Delorhynchus_ bears an infraorbital canal in
contrast to the groove in similar position in _Colobomycter_. The
recurvature of the four teeth present in the fragments of _Delorhynchus_
differs from that in the teeth of _Colobomycter_ in which only the
canine and precanine are recurved. Vaughn implies that anterior and
posterior cutting edges extend the length of the teeth in
_Colobomycter_; these are restricted to the distal third of the teeth in
_Delorhynchus_. The external surfaces of the maxillae of _Delorhynchus_
are pitted and ridged; Vaughn was unable to discern sculpturing of the
corresponding surfaces in _Colobomycter_.
_Delorhynchus_ resembles the nitosaurids in size, the shape and
sharpness of the teeth, their recurvature and the slight enlargement of
their bases, the exclusion of the lacrimal bone from the narial margin
(in _Mycterosaurus_) and the apparent lack of a special canine pair of
teeth. Resemblances to the caseids are to be noted in the enlargement of
the naris (4.5 mm. in height as opposed to 1.7 mm. in _Colobomycter_),
lack of development of canines, presence of an infraorbital canal (in
_Cotylorhynchus_) and absence of many replacement gaps in the marginal
row of teeth.
The absence of caniniform enlargement and the extension of the maxilla
dorsad of the naris exclude _Delorhynchus_ from the Eothyrididae
(Ophiacodontia) but are no bar to its inclusion in the Nitosauridae
(Edaphosauria). The marginal teeth of _Delorhynchus_ are simple and
primitive, being much like those of the nitosaurids that are described
in the literature.
The large narial opening and its posterior, dorsal and ventral enclosure
by the maxilla, the infraorbital canal, and the sculptured external
surfaces of the maxillary fragments indicate that _Delorhynchus_, in
these features at least, is close to achieving the caseid grade.