Dental variation in the molars of Mammuthus columbi var. M. imperator (Proboscidea, Elephantidae) from a Mathis gravel quarry, southern Texas
Introduction
A collection of 149 Mammuthus teeth and fragments of teeth was recovered in 1974 from a gravel quarry in southern Texas by E. Lundelius, and housed in the Texas Memorial Museum (TMM), Austin. The site, TMM 41724, is located near Mathis, San Patricio County, TX (Fig. 1). Fossil materials were exposed by a dragline operator, and specimens were collected at various levels within the gravel quarry. The exposed sedimentary section represents fluvial point bar deposits and contains lag gravels.
In addition to Mammuthus, the locality yielded the remains of Xenarthra, Equidae, Camelidae, Cervidae, and Bovidae. This attritional assemblage, presumably time-averaged, is late Rancholabrean in age (Lundelius, pers. comm., 1999).
The sample of 149 Mammuthus teeth possibly represents a minimum of 25 individuals, and provides an adequate base for metric and statistical analyses of dental variation. Enamel thickness and plate frequency exhibited by these teeth (Table 1, Table 2) approach that found in Irvingtonian age materials generally assigned to M. imperator (Maglio, 1973; Madden, 1981). M. imperator and M. columbi are considered conspecific by Agenbroad (2003). We concur with Agenbroad, and herein refer to materials that would have been placed in M. imperator as M. columbi var. M. imperator. The dental characteristics of the Mathis sample show that local level variation was present in the dentitions of late Pleistocene, Rancholabrean NALMA Mammuthus columbi from southern Texas, US.
Section snippets
Nomenclature, measurements and methods
Several systems of nomenclature have been proposed for Elephantidae cheek teeth. These are: Laws (1966), M1, M2, M3, M4, M5, M6; Saunders (1970) (follows Osborn, 1942), Dp2, Dp3, Dp4, M1, M2, M3; Sikes (1971), I, II, III, IV, V, VI; Madden (1981), dP2, dP3, dP4, M1, M2, M3; and Froelich and Kalb (1995), P2, P3, P4, M1, M2, M3. According to Haynes (1991), most modern paleontologists use Saunders’ (1970) nomenclature, while most field biologists, including Haynes, follow Laws’ (1966) system
Discussion and conclusions
The Mathis sample is not catastrophic, and does not represent a single elephantid herd. The specimens were recovered from different levels within the Mathis gravel quarry and appear to represent an attritional accumulation within the fluvial deposit. However, there is a taphonomic or sampling bias. No premolars were recovered, and the younger animals are not represented. The assemblage likely reflects an otherwise unbiased adult population.
Of the 149 teeth or fragments of teeth in the Mathis
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