Ectypodus lovei from the Medicine Pole Hills Local Fauna (Chadronian, latest Eocene), Bowman County N.D.
REFERRED SPECIMENS (all PRTM) PU 4984; LP4 4932, 4934; RP4 2068, 4932, 4935; LM 12029, 4840, 4842, 4925, 4928; RM1 1962, 2060; RM2 4937; Rp4 1328, 4938; Lp4 4927, 4933; Lm1 4841, 4930, 4936; Rm1 4931, 5481.
DESCRIPTION p4 The one complete p4 (PTRM 1328) has 8 serrations (and one pseudoserration). The crown is high and arched in profile view. There is a well defined posterobuccal ledge which descends from the most posterior serration, ml The cusp formula is 7:4-5. The two rows of cusps meet on the anterior margin of the tooth, m2 The sample contains no m2's. PU PTRM 4948 appears to represent an anterior premolar. It has a larger anterior-posterior dimension than lingual-buccal dimension. There is one dominant cusp which is on the buccal margin of the tooth and elongate in the anterior-posterior dimension. There are two accessory cusps, one is on the anterior margin of the tooth and the second cusp on the internal margin. P4 The P4 is gently arched in profile view. The anterior slope is straight and the posterior slope is straight to slightly concave. The lingual margin of the tooth is concave. The cusp formula is 2-3:5:0. The penultimate cusp is the tallest on the internal row. M1 The M1 is nearly rectangular in outline. In profile, the tooth is concave dorsally. The cusp formula is 6-8:8-9:4-6 and is highly variable. All cusps increase in size posteriorly. M2 The M2 is triangular in outline. The buccal and lingual margins are virtually straight although obliquely oriented. The cusp formula is 1:2:3.
DISCUSSION All of the identifiable multituberculates that have been reported from post-Bridgerian rocks have been assigned to Ectypodus and nothing in our sample suggests a different genus. Sloan's (5) original diagnosis of Parectypodus lovei is primarily based on partial P/p4's, although he does gives a description of the molars. Krishtalka and Black (6) transferred the species from Parectypodus to Ectypodus, based on the morphology of a nearly complete p4, which showed a straight anterior slope, characteristic of Ectypodus, rather than a convex anterior slope, which is characteristic of Parectypodus. The complete p4 (PTRM 1328) in our sample has a straight anterior slope, supporting their conclusion. The Medicine Pole Hills has a nearly complete dental arcade, with the first complete p4, the first complete P4 and the first possible anterior premolar, lacking only the m2 among the cheek teeth. The morphology and the size range of the teeth in the Medicine Pole Hills sample match that of Ectypodus lovei as described by Storer (7). The only differences are in the M1 which shows a slightly different cusp formula, with fewer cusps in the external row. The fact that there are more complete M1's from the Medicine Pole Hills which do not differ greatly in their morphology from E. lovei from the Badwater Local Fauna, Raben Ranch Local Fauna or Lac Pelletier Lower Fauna samples, strongly suggests that they all represent the same species. The variation in the rest of the dentition falls within the range of variation seen in these samples. These differences do not suggest the presence of a second species of Ectypodus, but rather variation within a variable population.
BIOCHRONOLOGY The identification of E. lovei from the Medicine Pole Hills Local Fauna does not support or contradict the existing age interpretation of the Medicine Pole Hills deposits (3) because E. lovei has been reported from the late Uintan (5) to the middle Chadronian (8).
(1.) Schumaker KK, Kihm AJ, Warner-Eavns C and Pearson DA (2001) Proc. N.D. Acad. Sci. 55,43.
(2.) Kihm AJ, Schumaker KK, Warner-Evans C and Pearson DA (200l) J. Vert. Paleo. v21(3) supplement pp 67A.
(3.) Heaton TH and Emry RJ (1996) in, The Terrestrial Eocene-Oligocene transition in North America, (Prothero DR and Emry RJ eds.), New York Cambridge University Press, pp. 581-608.
(4.) Clemens WA and Kielan-Jaworowska Z in Mesozoic Mammals, (Lillegraven JA, Kielan-Jaworowska Z and Clemesns WA eds.)
(5.) Sloan RE (1966) Annals Carnegie Mus. v. 38, art. 14, pp.309-315.
(6.) Krishtalka L and Black CC (1975) Annals Carnegie Mus. v. 45:15, pp. 287-297
(7.) Storer JE (1993) Canadian J. Earth Science v. 30.
(8.) Ostrander GE (1984) Trans. Nebraska Acad. Sci. 12 pp. 71-80.
Karew K. Schumaker *, Allen J. Kihm
Department of Geosciences, Minot State University, Minot
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|Title Annotation:||COMMUNICATIONS: UNDERGRADUATE|
|Author:||Schumaker, Karew K.; Kihm, Allen J.|
|Publication:||Proceedings of the North Dakota Academy of Science|
|Date:||Apr 1, 2002|
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