Mimotricentes tedfordi McKenna and Lofgren, 2003
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https://doi.org/ 10.1206/3797.1 |
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persistent identifier |
https://treatment.plazi.org/id/587387C9-142A-5178-FEFB-1B2EFCB2FC02 |
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Carolina |
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Mimotricentes tedfordi McKenna and Lofgren, 2003 |
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Mimotricentes tedfordi McKenna and Lofgren, 2003
HOLOTYPE: RAM 6908 , right maxilla with P4–M3 from RAM locality V94133 View Materials , member
4a, Goler Formation, California.
REFERRED SPECIMENS: RAM 15622, right dentary fragment with talonid of p4, and m1–2 from RAM locality V201014, member 4a ( fig. 6B–C View FIGURE 6 ); RAM 9670, left dentary fragment with the base of p4 and damaged m1 from RAM locality V200510, member 4a ( fig. 6D View FIGURE 6 ); RAM 6928, right dentary fragment with m3 talonid and base of trigonid ( fig. 6E View FIGURE 6 ), and RAM 15333, left M2 from RAM locality V200001, member 4a.
DISCUSSION: The holotype of M. tedfordi , a maxillary fragment with P4-M3 (RAM 6908), from V94133 View Materials , high in member 4a, was described by McKenna and Lofgren (2003), who noted that M. tedfordi was significantly smaller than M. subtrigonus and all other described species of Mimotricentes and Lambertocyon . The holotype was the only known specimen of Mimotricentes tedfordi , so the lower dentition was not described.
In 2010, a dentary fragment (RAM 15622) was recovered from V201014, a site low in member 4a, about 3 km south of the type locality of M. tedfordi . RAM 15622 represents the lower dentition of a small arctocyonid that almost certainly is M. tedfordi . Two other fragmentary arctocyonid dentaries (RAM 6928 and RAM 9670), collected prior to 2008, probably also represent M. tedfordi . Also, an isolated M2 (RAM 15333), found in 2012, is nearly identical to the M2 of the holotype. These four specimens are described below.
DESCRIPTION: The M 2 of the holotype of M. tedfordi ( RAM 6908 ) and RAM 15333 are similar in all features, their unusually large crestlike parastyles being especially noteworthy. Also, the length of RAM 15333 is 4.54 mm and the width 5.19 mm, dimensions similar to that of the M2 of the holotype (length 4.62 mm and width 5.50 mm) .
RAM 15622 is a dentary fragment with a broken p4, and m1–2, with only the talonid and posterior wall of the trigonid of the p4 preserved ( fig. 6B–C View FIGURE 6 ). The p4 has a low, 1.2 mm long, posterior shelf, which has a weakly developed posteromedial cusp connected to the trigonid wall by a small crest, features often seen in arctocyonids. The metaconid and protoconid of m1 are subequal in size and height, both larger than the low, labially shifted paraconid, and a protocristid and paracrista are present. The precingulid and a partial labial cingulid are present (labial cingulid terminates posteriorly at ectoflexid). The cristid obliqua is well developed and terminates at a large hypoconid, and a small but deep talonid basin, with steep posterior and labial slopes is present. A small posterolingually positioned entoconid and hypoconulid are closely appressed, with the hypoconulid slightly posterior to the transversely aligned hypoconid and entoconid. The m2 is similar to m 1 in most respects, but m2 is more quadrate in outline and has a more labially shifted paraconid. Depth of the mandible below m1 is 6.15 mm.
The p4 of RAM 9670 is sheared off just above the gum line and the anterior part of the tooth is missing ( fig. 6D View FIGURE 6 ), but its length was at least 3.5 mm, and width about 2.5 mm. The talonid of m1 is well preserved but the trigonid crown is missing due to breakage. The dimensions of the m1 of RAM 9670 are similar to those of the m1 of RAM 15622, but the talonid of RAM 9670 has crenulated enamel, a broader and shallower basin, and greater spacing of the entoconid and hypoconulid, differences suggesting they could represent different taxa. However, significant variation in lower molar morphology is well documented in Mimotricentes subtrigonus , a larger species than M. tedfordi ( table 7), from Swain Quarry in Wyoming, where sample sizes of isolated teeth can exceed 60 specimens ( Rigby, 1980: table 38). Teeth of M. subtrigonus exhibit considerable variation in talonid development, as the proximity of the hypoconuild and entoconid can vary from nearly fused to well separated with the hypoconulid medially located ( Rigby, 1980). Also, some m1s from Swain Quarry in the AMNH collections lack crenulated talonid enamel, while in others it is well developed. If this amount of variation is also present in M. tedfordi, RAM 9670 likely represents the same species as RAM 15622.
RAM 6928 is a dentary fragment with a damaged m3 that may also represent M. tedfordi . RAM 6928 has an intact m3 talonid, but its trigonid is broken at the gum line ( fig. 6E View FIGURE 6 ). The talonid has a low hypoconulid, an entoconid crest with three cuspules, and a large hypoconid. The talonid basin of m3 is broad and shallow and opens lingually through a small talonid notch. The morphology of the m3 talonid in Mimotricentes subtrigonus from Swain Quarry, varies even more than the m1 talonid, so much so that the m3 is “posteriorly too variable for taxonomic use” ( Rigby, 1980: 104). Specimens of M. subtrigonus observed at the AMNH from Swain Quarry have m3 talonids of similar construction as RAM 6928, but are much larger ( table 7). Thus, RAM 6928 probably also represents M. tedfordi .
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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