Fauna of the Vale and Choza : Diadectes, Xenacanthus, and specimens of uncertain affinities

UNI" -RSITY OF
ILLIujis LIBRARY

AT URBANA-CHAMPAIGN
NATURAL HIST. SURVEY

FIELDIANA • GEOLOGY

Published by
CHICAGO NATURAL HISTORY MUSEUM

Volume 10 May 31, 1956 No. 27

FAUNA OF THE VALE AND CHOZA: 13

Diadectes, Xenacanthus, and Specimens of
Uncertain Affinities

Everett Claire Olson

Research Associate, Division of Paleontology
Professor of Verteibrate Paleontology, Univbrsity of Chicago

INTRODUCTION

In the previous twelve papers of this series, genera and species for
which considerable information was available have been discussed.
Most of these could be placed with confidence in supergeneric
categories and details of their morphology could be presented. The
collections from the Vale and Choza contain a few specimens that
cannot be referred to known genera but are inadequate for generic
description, and fragments of known genera that have not been
considered before, since there is little definitive knowledge about
their associations and occurrences. These are taken up in the
present paper.

CLASS REPTILIA

Subclass Parareptilia

Infraclass Diadecta

Family Diadectidae

Diadectes sp.

Until recently it appeared that Diadectes, a relatively common
genus of the Wichita and early Clear Fork, was not present in the
Vale (Olson, 1952). A single vertebra, CNHM-UR 270, was dis-
covered in the early deposits of western Baylor County in 1952.
The vertebra is in a fair state of preservation and its generic assign-
ment poses no problem. There is, however, no morphological basis
for specific assignment, for the vertebrae of this genus are not
specifically diagnostic. It seems probable that the specimen pertains

No. 797 329

330 FIELDIANA: GEOLOGY, VOLUME 10

to the species D. tenuitecis, since this is the only species present
in the underlying Arroyo. It may, of course, represent an un-
described species.

The vertebra was found in a channel fill composed of fine con-
glomerate, about 100 feet above the base of the Vale Formation.
There can be no question of its stratigraphic position. Diadectes
becomes increasingly rare from the base to the top of the Arroyo.
This single specimen constitutes the only evidence that it continued
into the Vale. It is, of course, conceivable that the specimen was
introduced into the Vale by a reworking of Arroyo materials, but
there is no positive evidence in this direction. No trace of Diadectes
has been found as yet in the middle of late Vale or in the Choza.
Specimens may eventually turn up, but very extensive collecting
has not produced even a scrap that can be assigned to the genus.

Class CHONDRICHTHYES

Subclass Elamosbranchii

Order Xenacanthodii

Family Xenacanthidae

Xenacanthus cf. platypternus

From the standpoint of abundance, the fresh-water shark
Xenacanthus is in marked contrast to Diadectes, for remains of the
genus are common from the base to the top of the Vale and occur
sporadically from the base of the Choza to the highest producing
beds in the middle of this formation. Remains are predominantly
teeth and fragments of calcified cartilage. A crushed, but otherwise
well-preserved specimen that consists of a chondro-cranium, jaws
and visceral arches, CNHM-UF 566, has been found in the lower
Vale in the Crooked Creek area. A second specimen, CNHM-UF
565, consisting of impressions of jaws and gill supports, has come
from beds transitional between the Vale and the Choza, at locality
KK, in Knox County, Texas.

Teeth are abundant in many of the channel deposits in the Vale
and also occur in pond deposits at various levels in this Formation.
This is in contrast to the Arroyo below and Choza above, in which
remains of Xenacanthus appear to be confined to stream deposits.
The highest known occurrence of Xenacanthus in the Clear Fork
is in beds of mid-Choza age, in Foard County, Texas. A few teeth
occur in channel conglomerates at this level. The genus is known.

OLSON: FAUNA OF VALE AND CHOZA 331

however, from the overlying San Angelo Formation of Texas (Olson
and Beerbower, 1953).

It is difficult to assign the known materials to species or to
know whether one or more species were present. The teeth appear
to be relatively uniform, except for size, throughout the Vale and
Choza, and to conform closely to those of Xenacanthus platypternus
(Cope) as described by Hotton (1952). As he noted, the jaw carti-
lages, at least at present, are of little aid in separation of X. texensis
and X. platypternus, the two Texas species. In view of the resem-
blances of the teeth from the Vale and Choza to those of X. platyp-
ternus, of the Arroyo, it is probable that the sharks from these
deposits were closely related to, perhaps identical with, this species.
Tentative assignment has thus been made.

Class REPTILIA

Subclass Eureptilia

Order Pelycosauria
Suborder Edaphosauria
Family Edaphosauridae

Genus nov., unnamed

The specimen that is the basis for the following discussion
consists of a single toothed palate (CNHM-UR 29) from locality
KC of the upper Vale. Figure 135 is a semi-diagrammatic represen-
tation of the specimen. The preserved part consists of a plate of
bone about 5 inches long, which is set with 8 rows of more or less
regularly spaced teeth. The crowns of the teeth are bluntly conical
and the bases are set firmly in bone. As shown in the figure, one
row of teeth splits into two anteriorly.

The specimen was found in a channel fill composed of clay pebble
conglomerate. It was in direct association with Diplocaulus, and
in the immediate vicinity, in lateral off-channel deposits, Captorhinus
was present. No other specimens that can definitely be assigned
to the genus have been found in the Vale, in spite of the ease of
recognition of the palatal teeth and the excessive size of the animal
as indicated by the palate. Whether this animal lived in the area
or was washed in from another life zone cannot be determined,
although the failure to find other specimens suggests that the second
interpretation may be correct.

Fig. 135. Palate of new genus of reptile (unnamed), CNHM-UR 29; X H-

Fig. 136. Scapulo-coracoid
of unnamed genus of ?reptile,
CNHM-UR 268; X Ji-

332

OLSON: FAUNA OF VALE AND CHOZA 333

It is probable that the animal represented by the palate was
a reptile, for no known amphibian even vaguely resembles it in the
formation of the palate. Among the reptiles, the most probable
relationships are with the edaphosaurids, in which toothed palates
are characteristic. It differs from other known genera of edapho-
saurids in size and the regularity of the rows of teeth. The possibility
that the palate represents a captorhinomorph, rather than an
edaphosaurid, cannot be ruled out. The captorhinomorphs of the
Vale and Choza had multiple rows of teeth, and in Labidosaurikos
and Captorhinikos these were arrayed in more or less regular rows.
Palatal teeth were not, however, strongly developed in these genera.
In Rothia, from the San Angelo, long, irregularly placed palatal
teeth were present, but the pattern was very different from that
seen in the specimen under consideration. Waggoneria, which has
been tentatively assigned to the Seymouriamorpha, had palatal
teeth, but these were arrayed in a roughly crescentic pattern. There
seems little chance that the new genus could be related to this
group.

Edaphosaurus, the only well-known edaphosaurid of the Arroyo,
had strongly developed, blunt palatal teeth. The arrangement,
however, is irregular and not like that in the Vale specimen. Modifi-
cations of the general Edaphosaurus pattern could have produced
the condition shown in figure 135. If the animal is an edaphosaurid,
it must have been of truly gigantic proportions, for the edaphosaurid
head is notably small in proportion to the trunk and limbs. Although
the specimen clearly does not pertain to any known genus, it is too
fragmentary to serve as a suitable type and, for this reason, has
not been named, pending the discovery of more adequate materials.

Class REPTILIA
Genus nov., incertae sedis

A second puzzling specimen (CNHM-UR 268), from locality KD
in the upper Vale, consists of a large scapulo-coracoid in a very poor
state of preservation. In spite of the lack of detail, it is evident
that this specimen does not pertain to any previously known genus.
The scapular blade is over 10 inches tall and very narrow at the
base (fig. 136) . Details of the lower part of the scapula and coracoid
are obscured by the presence of a large mass of gypsum that crystal-
lized within the bone between the medial and lateral surfaces.

There is no known reptile or amphibian from the Arroyo, Vale or
Choza that closely resembles this specimen. The general charac-

334 FIELDIANA: GEOLOGY, VOLUME 10

teristics appear to be reptilian rather than amphibian. The closest
resemblance to any known genus is to Tappenosaurus of the San
Angelo and Flower Pot Formations, which overlie the Clear Fork.
It would be foolhardy, however, from the available evidence, to
suggest a real affinity to this genus. It is possible that this specimen
and the palate, CNHM-UR 29, described above, are parts of mem-
bers of the same genus or species, for there is no barrier in size, and
they occur at the same level in the Vale. Outside of these facts,
however, there is no concrete evidence to support this idea.

The most probable explanation for this specimen, and for the
palate noted above, is that they are from animals that were not
characteristic of the fauna of the Vale deltaic area, but were brought
in by physical transportation, or, perhaps, strayed into the area
from their more characteristic habitat.

REFERENCES

HoTTON, Nicholas, III
1952. Jaws and teeth of American xenacanth sharks. Jour. Paleon., 26,
pp. 489-500, 1 pi.

Olson, E. C.

1952. The evolution of a Permian vertebrate chronofauna. Evolution, 6,
pp. 188-196, 5 figs.

Olson, E. C, and Beerbower, J. R.

1953. The San Angelo Formation, Permian of Texas, and its vertebrates.
Jour. Geol., 61, pp. 389-423, 10 figs.