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A late Pleistocene herpetofauna from the lower Texas Panhandle.

ABSTRACT. -- The amphibians and reptiles contained in the Carrol Creek local fauna were found in a late Pleistocene sinkhole deposit in Donley County of the lower Texas Panhandle. A radiocarbon date of 32,400 [+ or -] 560 years before present was obtained from a sample of mollusk shells. The herpetofauna, represented by 12 taxa (10 genera and six species), gives evidence of at least a semiaquatic environment near the fossil site during the late Pleistocene. All represented taxa are found near the Carrol Creek deposit today, indicating there was little effect on the Texas Panhandle herpetofaunal assemblage by environmental and climatic changes in the late Pleistocene. Key words: fossil herpetofauna; Pleistocene; Texas Panhandle.

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A herpetofauna containing at least one salamander, one frog, one lizard, and nine snakes is reported herein from the late Pleistocene Carrol Creek local fauna, Donley County, Texas. The study area is located on the west side of Carrol Creek, approximately 13 kilometers north of Clarendon and 1.5 kilometers west of Highway 70. The fossil deposit, considered to be a stream-bed sinkhole filling, was formed when dissolving gypsum beds from the underlying Permian rocks caused an abrupt slumping (Kasper, 1989). Mollusks and small vertebrates were washed into the depression as it filled with clay and fine sand. Modern Carrol Creek is a permanent stream that flows almost due south into Greenbelt Reservoir, an impoundment of the Salt Fork of the Red River.

Approximately 3375 kilograms of matrix were sampled and screenwashed from the fossil deposit. A large sample of mollusk shells from the site was radiocarbon dated at 32,400 [+ or -] 560 years before present (Beta Analytic Inc., Beta-25354). Numerous fish bones, including abundant catfish spines, were found but not studied, and two fragmentary bird bones could not be identified. Kasper (1989) reported two plant fossils and 17 mammalian taxa in the Carrol Creek fauna.

ACCOUNTS OF SPECIES

In the following accounts of species, catalog numbers (in parentheses) refer to specimens housed in the Midwestern State University Collection of Fossil Vertebrates. The herpetological skeletal collection of Georgia College was used to make taxonomic determinations.

Ambystoma tigrinum (Green)

The one vertebra (12525) is badly damaged, but it is clearly like Ambystoma tigrinum based on its relatively large size and upswept neural arch (Holman, 1969). This species is the only salamander found in Donley County today (Dixon, 1987), where it probably spends most of its time burrowed beneath the ground.

Rana sp. indet.

The material includes one scapula and one ilium (12523). The scapula is like those of Rana and differs from Bufo and Scaphiopus in that the coracoid articular process is close to the clavicular articular process, which creates a narrow glenoid opening. In Bufo and Scaphiopus, the clavicular process projects laterally, resulting in a wider glenoid opening. Ranid scapulae do not appear to be specifically diagnostic.

The ilium is badly worn, but the remnant of a well-developed ilial blade and lack of a dorsal prominence-protuberance complex is distinctive of ranid species. The fossil ilium represents a rather small ranid about the size of living Rana blairi, the only leopard frog presently found at Carrol Creek (Dixon, 1987).

Cnemidophorus sp. indet.

The fragmentary dentary (12526) is characteristic of the genus Cnemidophorus based on its narrow, tapering shape, subpleurodont trilobed teeth, and Meckel's groove open to the symphysis (Estes and Tihen, 1964). Although three species of Cnemidophorus have present distributions that include (or are near) the fossil site (Dixon, 1987), specific determination cannot be made using dentary characteristics.

Coluber sp. indet. or Masticophis sp. indet.

The genera Coluber and Masticophis cannot be separated based upon vertebral characters (Holman, 1969, 1979; Parmley, 1986a). The two fossil vertebrae (12527; Fig. 1C-D) from Carrol Creek are easily identified to Coluber (=Masticophis) by their long, narrow shape, long accessory processes, relatively low and long neural spines, and uniformly narrow hemal keels (Parmley, 1988a). The species Coluber constrictor and Masticophis flagellum are common prairie snakes in the Texas Panhandle (Dixon, 1987).

Elaphe guttata (Linnaeus) or Elaphe obsoleta (James)

The two vertebrae (12528) have higher neural arches than those of similar-sized species of Lampropeltis, but lower than those of Pituophis. The specimens are similar in size and subcentral ridge development to Elaphe guttata and E. obsoleta, which are difficult to separate on the basis of vertebral characters (Parmley, 1986b). Elaphe guttata occurs in Donley County today (Dixon, 1987), and E. obsoleta is found near enough to have lived at Carrol Creek 32,000 years ago.

[FIGURE 1 OMITTED]

Heterodon sp. indet.

Although too fragmentary for specific identification, the two vertebrae (12558; Fig. 1E-F) clearly represent the genus Heterodon based upon the depressed neural arches, the wide and obsolete hemal keels, and weakly developed subcentral ridges (Holman, 1962; Parmley, 1988b). Both Texas species, Heterodon nasicus and H. platyrhinos, occur in Donley County today (Dixon, 1987).

Lampropeltis triangulum (Lacepede)

Trunk vertebrae of Lampropeltis triangulum (at least those from midcontinental North America) are distinctive based on their small size, low neural spines, depressed neural arches, and moderately to poorly developed hemal keels (Parmley, 1988b). The Carrol Creek fossil (one vertebra, 12529) is similar to those of smaller individuals of L. triangulum, which occurs throughout the Texas Panhandle today (Dixon, 1987).

Lampropeltis cf. getulus (Linnaeus)

Vertebrae of Lampropeltis getulus and L. calligaster are difficult to distinguish. One Carrol Creek vertebra (12530) is cautiously referred to L. getulus based on the presence of a flat zygosphene (usually arched in L. calligaster), better developed hemal keels, and relatively higher neural spines. Both species occur near the fossil site today (Dixon, 1987).

Nerodia erythrogaster (Forster)

The single fossil vertebra (12557; Fig. 1A-B) is placed in the genus Nerodia rather than Thamnophis or Regina based on the short and wide dorsal neural arch region (Brattstrom, 1967), vaulted neural arch, higher neural spine, and the wide, ventrally directed hypapophysis. The fossil has a higher neural spine than specimens of N. sipedon, but lower than that of N. rhombifera. Modern specimens of N. erythrogaster match the fossil vertebra in all respects, representing a small individual of the species. Nerodia erythrogaster is the only species of Nerodia presently occurring in the Texas Panhandle (Dixon, 1987).

Thamnophis cf. proximus (James) or sirtalis (Linnaeus)

The two vertebrae (12531) are similar to specimens of the genus Thamnophis and differ from those of Nerodia and Regina in being more gracile, narrower through the neural arch region, and in having narrower, more posteriorly directed hypapophyses (Parmley, 1988b). The fossil vertebrae are like those of Thamnophis proximus and T. sirtalis (which are difficult to separate) in being rather elongate and gracile in form, with high neural spines that are weakly concave along the anterior and posterior borders (Parmley, 1988a). Thamnophis proximus presently occurs at Carrol Creek, and T. sirtalis is recorded in the adjoining county (Dixon, 1987).

Thamnophis sp. indet.

Nine vertebrae (12532) are assigned to the genus Thamnophis based on the characters discussed above, but they are too fragmentary for specific identification.

Crotalus sp. indet.

The Carrol Creek fossil vertebra (12533) is wide through the middorsal neural arch region, has a thick, posteriorly directed hypapophysis, and has a moderately depressed neural arch (in posterior view), as in modern crotaline vertebrae. The presence of small cotylar foramina set in shallow pits suggests the genus Crotalus, rather than Agkistrodon or Sistrurus (Parmley, 1988b). Crotalus atrox and C. viridis presently have distributions that include Carrol Creek (Dixon, 1987).

DISCUSSION

Included in the Carrol Creek herpetofauna are 12 taxa encompassing 10 genera and six species, of which several taxa indicate an aquatic environment. The presence of a tiger salmander (Ambystoma tigrinum) and a small leopard frog (Rana sp.) indicates permanent water, needed for reproduction, at Carrol Creek 32,000 years ago. Also indicating mesic habitat are a water snake (Nerodia erythrogaster), two garter or ribbon snakes (Thamnophis sp., and T. proximus or T. sirtalis), and a hog-nosed snake (Heterodon sp.). These taxa prefer wetland environments where they mainly prey on fish, frogs, and tadpoles. The remaining six reptilian taxa are not habitat specific, and could have lived either on nearby prairie or been associated with an aquatic environment, as they do today.

As far as can be determined, the entire Carrol Creek herpetofauna is represented by living taxa, and the fossil site is within or near their modern distributions (Dixon, 1987), indicating little change has occurred in the herpetofaunal assemblage of the Texas Panhandle over the past 32,000 years. In contrast, the Carrol Creek mammalian fauna, with four extinct and three extralimital taxa, provides evidence of major environmental change. Most of the mammals are indigenous prairie taxa, but several extralimital and extinct species support evidence of a marshy, riparian zone, and a more equable, moister climate than is present today at Carrol Creek (Kasper, 1989). Thus, while late Pleistocene environmental and climatic changes can be associated with the local and final extinction of select Carrol Creek mammalian species, these changes appear to have had nominal effect on the herpetofauna of the Texas Panhandle. However, it should be noted that other late Pleistocene faunas of Texas do include extralimital herpetological species, showing that at least minor herpetofaunal shifts from the late Pleistocene to the Recent did occur (see, for example, Parmley, 1986a, 1990).

We thank F. B. Stangl, Jr., for critical review of the manuscript. Artist time was kindly made available by J. Alan Holman of the Michigan State University Museum. Drawings were made by Irene Rinchetti, MSU Museum staff artist.

LITERATURE CITED

Brattstrom, B. H. 1967. A succession of Pliocene and Pleistocene snake faunas from the High Plains of the United States. Copeia, 1967:188-202.

Dixon, J. R. 1987. Amphibians and reptiles of Texas. Texas A & M Univ. Press, College Station, xii + 434 pp.

Estes, R., and J. A. Tihen. 1964. Lower vertebrates from the Valentine Formation of Nebraska. Amer. Midland Nat., 72:453-472.

Holman, J. A. 1962. A Texas Pleistocene herpetofauna. Copeia, 1962:255-261.

______. 1969. Herpetofauna of the Pleistocene Slaton local fauna of Texas. Southwestern Nat., 14:203-212.

______. 1979. A review of North American Tertiary snakes. Publ. Mus. Michigan State Univ., Paleo. Ser., 1:203-260.

Kasper, S. 1989. Vertebrates from the late Pleistocene Carrol Creek local fauna, Donley County, Texas. Unpublished M.S. thesis, Midwestern State Univ., Wichita Falls, Texas, 65 pp.

Parmley, D. 1986a. Herpetofauna of the Rancholabrean Schulze Cave local fauna of Texas. J. Herpetol., 20:1-10.

______. 1986b. An annotated key to isolated trunk vertebrate of Elaphe (Colubridae) species occurring in Texas. Texas J. Sci., 38:41-44.

______. 1988a. Early Hemphillian (late Miocene) snakes from the Higgins local fauna of Lipscomb County, Texas. J. Vert. Paleo., 8:322-327.

______. 1988b. Middle Holocene herpetofauna of Klein Cave, Kerr County, Texas. Southwestern Nat., 33:378-382.

______. 1990. Late Pleistocene snakes from Fowlkes Cave, Culberson County, Texas. J. Herpetol., 24:266-274.

STEPHEN KASPER AND DENNIS PARMLEY

Department of Biology, Midwestern State University, Wichita Falls, Texas 76308, and Department of Biological and Environmental Sciences, Georgia College, Milledgeville, Georgia 31061
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Author:Kasper, Stephen; Parmley, Dennis
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:Aug 1, 1990
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