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Full text of "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.