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The fossil carnivores of the turtle butte assemblage (Arikareean), Tripp County, South Dakota.

Introduction--The Turtle Butte Formation, exposed on Turtle Butte in Tripp County, south-central South Dakota, has yielded a diverse paleofauna. The Turtle Butte Formagon and Weiler local fauna were first described in 1968 (1). In 1969 and 1973, a field crew from the South Dakota School of Mines and Technology, collected fossil specimens and fossiliferous matrix from the Turtle Butte Formation, which was later studied by Schumaker [2]. In 2004, a very small sample of bulk matrix was collected by Bailey (3). On the basis of biostratlgraphic analyses completed by Skinner et al.( 13, Bailey (3), and Schumaker (2), the Turtle Butte Assemblage was determined to be late early Arikareean in age.

Results--Confident identification of the Turtle Butte Assemblage carnivores to the species level is difficult because the fossil specimens are fragmentary or isolated teeth. Five distinct carnivore taxa are represented in 1he Turtle Butte Assemblage representing two suborders, the Cynoidea and the Arctoidea and are discussed below.

Hesperocyoninae gen. indet. (SDSM 82103)--Wang's (5) diagnosis for the subfamily is based on cranial characters and dental characters of P4, M1, and m1 which cannot be used to determine the identification of the tooth and "the subfamily is mainly defined by its lack of synapomorphics for the other two subfamilies." The lack of the paraconule and metaconule suggest a primitive morphology and support the assignment to the Hesperocyoninae.

Borophaginae gen indet. (SDSM 82106)--The low, bulbous, robust nature of the tooth suggests that it belongs to the Subfamily Borophaginae, which is typically characterized as having robust teeth for crushing bone. The measurements of SDSM 82106 compare favorably with species of Archaeocyon and Cynarctoides.

Cynarctoides roii (SDSM 82104)--Cynarctoides is characterized by long, narrow premolars, conical and high-crowned cusps in the lower molars, higher metaconids, larger protostylids in lower molars. SDSM 82104 exhibits tall, conical cusps on the trigonid and a nearly identical size and morphology to the paratype specimen.

Amphicyonidae gen. indet (SDSM 82105) The isolated nature of the tooth and the lack of known deciduous dentition of late Oligocene early Miocene carnivores does not allow for assignment of this specimen to genus. In general, the P4 of amphicyonids is laterally compressed and the protocone is nearly in line with the paracone and metacone as exhibited by SDSM 82105.

Nothocyon n.sp. (SDSM 8640, 82107) The genus Nothocyon has a complicated taxonomic history. Recent revisions of the monospecific genus, has left two specimens assigned In N. geismarianus with other specimens previously assigned to the genus now placed within several other taxa (4 and 5). N. geismarianus is characterized by an m I with a low, short trigonid with the metaconid slightly more posterior than the protoconid, a large talonid, subequal entoconid and hypoconid, compressed m2 trigonid with an anterobuccal cingulid, and a very small paraconid SDSM 8640 differs from N geismarianus in that the length of the ml is not as reduced and has a lesser degree of trigonid compression on the m2. These differences are not significant enough to consider assignment of the specimen to any genus other than Nothocyon. However, due to the complicated taxonomic history, a heuristic search using parsimony was completed to support the interpretation. The resulting strict consensus tree placed the SDSM specimens as a sister taxon to N geismarianus within the Arctoid clade, supporting the initial interpretation that these specimens belong in the genus Nothocyon. The differences between N. geismarianus and the SDSM specimens may be attributed to one of two factors First, small sample sizes do not allow for the assessment individual variation. Second, the SDSM specimens represent a new species of Nothocyon, as they exhibit, but to a lesser extent, the derived characteristics of a compressed m2 trigonid and a shortened m1 trigonid as N. geismarianus. The differences are significant enough to support the identification of the SDSM specimens as a distinct species of Nothocyon. Identification of the Turtle Butte Assemblage specimens as Nothocyon represents both age and geographic range extensions for the genus from the early late Arikareean to the late early Arikareean.

Conclusions--Despite the limited identifications, the fossil specimens show that the Turtle Butte Assemblage has a diverse carnivore component with five distinct carnivore taxa, Three canid and two arctoid carnivores are present in the assemblage. The presence of a new species of Nothocyon represents an age range extension for the genus.

References:

(1) Skinner M, S Skinner, R Gooris. (1968). Bull. Amer. Mus. Nat. Hist. 138(7):379-436.

(2) Schumaker K. (2009). Proc. ND Acad. Sci. 63:64,

(3) Bailey B. (2004). Paludicola. 4(3):81-113.

(4) Wang X, R Tedford. (1992). J. of Vert. Palco. 12[2]:223-229

(5) Wang X, R Tedford, B Taylor. (1999) Bull. Am. Mus. Nat. Hist. 243, 391p.

Karew K. Sehumaker [1], Matthew W. Weiler [1], and Rebecca Simmons [2]

[1] Department of Geology and Geological Engineering, [2] Department of Biology, University of North Dakota, Grand Forks, ND 58202
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Title Annotation:Graduate Communication in the A. Roger Denison competition
Author:Schumaker, Karew K.; Weiler, Matthew W.; Simmons, Rebecca
Publication:Proceedings of the North Dakota Academy of Science
Date:Apr 1, 2010
Words:814
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