Chadronia sp.
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publication ID |
https://doi.org/ 10.4202/app.2011.0045 |
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persistent identifier |
https://treatment.plazi.org/id/90525533-121C-BA5E-DC4F-FD10FA3B9FA8 |
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treatment provided by |
Felipe |
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scientific name |
Chadronia sp. |
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Fig. 3 View Fig .
Material.— BADL 16917 , anterior portion of mandible with broken lower canines and the alveoli for p1–2 from “Owl’s Roost” locality (BADL-LOC-0236), North Unit of Badlands National Park , South Dakota, USA; Scenic Member of the Brule Formation (Early Oligocene) .
Description.— In anterior view, the mandible is distinctively concave dorsally and convex ventrally ( Fig. 3D View Fig ). The mandibular symphysis is very robust, extending from the anterior margin of the mandible to beyond the preserved posterior border of the specimen ( Fig. 3B View Fig ). The canines are separated by a 4.48 mm wide anterior extension of the mandible, which appears to have been highly vascularized ( Fig. 3B View Fig ). On the ventral surface there are two ovate foramina, one on each side of the mandibular symphysis ( Fig. 3C, D View Fig ). Muscle scars are present along the midline of the ventral surface ( Fig. 3C, D View Fig ). The latter is highly vascularized, with the density of vascularization increasing anterodorsally. Prominent, circular mental foramina are present (approximately 2.0 mm in diameter) on the lateral surfaces, just ventral to the anterior alveolus of p1 ( Fig. 3A View Fig ), which resembles that of Pantolestes sp. (FMNH PM 55996).
Incisors are lacking in the mandible of BADL 16917, as indicated by the absence of alveoli anterior to the canines. The enlarged lower canines are oriented anterodorsally, but broken just anterior to the level of the alveoli ( Fig. 3A, C View Fig ). The preserved portions of the canines are ovate in cross-section, with enamel remaining on the buccal, ventral, and partially on the dorsal margins of the teeth ( Fig. 3B, D View Fig ). The curvature of the canine cannot be confidently assessed, although it seems to have been recurved dorsally ( Fig. 3B View Fig ). Judging from the alveoli, p1 is double rooted with the roots angled posteroventrally into the mandible. The alveoli for p2 are slightly larger than those for p1, and its roots are angled more strongly posteriorly. Additionally, the p2 alveoli are obliquely oriented anterobuccally-posterolingually ( Fig. 3B View Fig ). See Table 1 for measurements of the preserved alveoli. Remarks.— Based on comparison with casts of the holotype of Chadronia margaretae Cook, 1954 (AMNH HC 750), we tentatively refer this specimen to Chadronia sp. The only potential difference may be the presence of at least one lower incisor in AMNH HC 750 ( Cook 1954). However, this observation was based on Cook’s interpretation of associated fragments that were inferred to belong to the mandible, which is incomplete anterior to the enlarged lower canine in the holotype. In BADL 16917, the anteriormost portion of the mandible is complete and does not show any signs of an incisor ( Fig. 3B, C, D View Fig ). This difference may represent species-level variation between the Late Chadronian (Ch4; Gunnell and Bloch 2008) holotype and the Orellan (Or1) referred specimen, although this is currently difficult to determine given the small number of available specimens. Alternatively, the referral of the isolated incisor by Cook (1954) to the holotype mandible may be incorrect. Based on this difference and given the incomplete nature of BADL 16917, we refrain from referring this specimen to the species level at this time.
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