Lambertocyon, Gingerich, 1979
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publication ID |
https://doi.org/ 10.1206/3797.1 |
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persistent identifier |
https://treatment.plazi.org/id/587387C9-142D-517B-FE13-1955FC7EF97F |
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treatment provided by |
Carolina |
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scientific name |
Lambertocyon |
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Lambertocyon cf. L. gingerichi Gunnell, 1994
HOLOTYPE: UM 81147 , left M1 from Chappo Type Locality, Wasatch Formation , Wyoming.
REFERRED SPECIMENS: RAM 9040, right M1 ( fig. 6F View FIGURE 6 ), and RAM 9043, left p3 fragment ( fig. 6G View FIGURE 6 ) from RAM locality V200001, member 4a.
DESCRIPTION: RAM 9040 is an unworn M1 that is in pristine condition except for the metacone, which is missing due to breakage ( fig. 6F View FIGURE 6 ). Based on the size of its base, the metacone was about as tall and broad as the large paracone. The protocone is massive, taller and larger than the paracone. A small and low hypocone is positioned slightly lingual to the protocone on the posterolingual corner of the postcingulum. The paraconule is larger than the metaconule, and a postparaconule wing connects the paraconule with the lingual base of the paracone (a premetaconule wing is not developed). The parastyle is large and crescent shaped, but a metastyle is not present. The lingual cingulum is complete, but weakly developed across the base of the protocone. The labial cingulum is also complete, but is weakest labial to the base of the paracone. The mesostyle is large and elongate, with its apex forming a large part of the labial cingulum. Also, a series of cuspules are present on the anteroposterior axis of the mesostyle and a small ridge projects lingually from its apex to the base of the cusp.
RAM 9043 is broken and only the anterolabial third of the tooth is present ( fig. 6G View FIGURE 6 ), but what remains is nearly identical in morphology to p3s of L. gingerichi from the Chappo Type Locality. Distinct enamel crenulations on the anterolabial face of p3, its size, and the wear facet on its broken crown all mirror features observed in Lambertocyon .
DISCUSSION: Three species of Lambertocyon have been described, L. ischyrus ( Gingerich, 1978, 1979), L. eximius ( Gingerich, 1979) , and L. gingerichi ( Gunnell, 1994) , with the following reported occurrences: (1) L. ischyrus, Debeque Formation , Colorado ( Gingerich, 1978, 1979; Kihm, 1984); (2) L. eximius, Blacks Peak Formation , Texas, ( Schiebout, 1974; listed as Arctocyonidae , undescribed genus and species), Fort Union Formation, Wyoming (Winterfeld, 1982), and Polecat Bench Formation, Wyoming ( Gingerich, 1979; Secord, 2008); and (3) L. gingerichi, Polecat Bench and Wasatch formations, Wyoming ( Gunnell, 1994; Secord, 2008). The Goler specimens of Lambertocyon are both from the Land of Oz site (V200001), so they almost certainly represent the same species.
Species of Lambertocyon are differentiated by mesostyle development and size, with L. eximius significantly larger than L. ischyrus ( Gingerich, 1979) , and L. gingerichi 8%–10% larger than L. eximius (on average) and also having a well-developed mesostyle ( Gunnell, 1994). Based on size, RAM 9040 is more like the holotype of L. eximus than the holotype of L. gingerichi , but measurements of the two species overlap ( table 8), demonstrating that distinguishing species of Lambertocyon by size is problematic. For example, the sample of Lambertocyon from Divide Quarry was referred to L. gingerichi ( Secord, 2008) , but one of the two M1s from Divide Quarry (UM 87040), has a length of 7.7 mm and a width of 8.1 mm ( table 8), dimensions closer to the holotype of L. eximus , than that of L. gingerichi ( table 8). The only reported M1 of L. ischyrus (FMNH P15545) is 6.86 mm in length and 7.87 mm in width, which is significantly smaller than M1s of L. eximius and L. gingerichi ( table 8).
The very large mesostyle of RAM 9040 is unique for Lambertocyon . Secord (2008) noted that M1 mesostyle development varies from strong to weak in L. gingerichi from Divide Quarry and larger samples are needed to conclusively demonstrate L. eximius and L. gingerichi are distinct species. RAM 9040 was compared directly to M1s of L. gingerichi (UM 81147 holotype and UM 85163 from Chappo Type locality; UM 87040 and UM 110259 from Divide Quarry), and these specimens have small mesostyles, in comparison to the distinctly larger mesostyle of RAM 9040. Also, the complete lingual cingulum of RAM 9040 is not reported for any M1 of Lambertocyon or observed in M1s of L. gingerichi from Chappo Type Locality or Divide Quarry.
The large mesostyle and complete lingual cingulum of RAM 9040 demonstrate that morphological variation within Lambertocyon is greater than previously documented and the Goler Formation occurrence may represent a new species. RAM 9043, the fragmentary p3, adds little to this discussion. An unusually large mesostyle and a weak but complete lingual cingulum on a single tooth is an inadequate basis from which to diagnose a new species, especially considering L. eximius and L. gingerichi require larger samples to confirm they represent distinct species. Thus, RAM 9040 and RAM 9043 are referred to Lambertocyon cf. L. gingerichi until more specimens of Lambertocyon are recovered from the Goler Formation, as the mesostyle development of RAM 9040 is more aligned with that species than L. eximus .
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