Orthacanthus? donnelljohnsi, Johnson & Thayer, 2009
|
publication ID |
https://doi.org/ 10.4202/app.2008.0051 |
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persistent identifier |
https://treatment.plazi.org/id/03802969-2236-8050-AE06-74ECFE489D8F |
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treatment provided by |
Felipe |
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scientific name |
Orthacanthus? donnelljohnsi |
| status |
sp. nov. |
Orthacanthus? donnelljohnsi sp. nov.
Fig. 10 View Fig .
Material.—UAPL 23487 (two posterior teeth) and UAPL 23494 (posterolateral tooth).
Description.— Two adult posterior teeth. One with 1.47 mm (am−pl) × 1.54 mm (l−l) base, very small central foramen, extremely subdued apical button, basal tubercle less so, three prominent aboral and one prominent oral foramina; principal cusps either broken or very short, straight, “recumbent” (crown−base angle ~135°), appear to be fused at their base; intermediate cusp absent. Second tooth with 2.32 mm (am−pl) × 2.83 mm (l−l) base, central foramen?present, subdued apical button isolated from cusps, basal tubercle subdued with convex surface, three prominent and two smaller aboral foramina, one prominent and Ẑ four smaller oral foramina; principal cusps with broken bases, appear to lean posteriorly; intermediate cusp absent.
One adult posterolateral tooth ( Fig. 10 View Fig ) with 1.54 mm (am−pl) × 1.19 mm (l−l) thin base, prominent central foramen, round apical button isolated from cusps, with prominent lingual extension, am−pl oval convex basal tubercle with subdued lingual extension reaching center of base, Ẑ two prominent aboral foramina (matrix interference) and two prominent plus one or two smaller oral foramina; both principal cusps complete, labio−lingually compressed, major cusp slightly longer, leaning posteriorly, minor cusp straight, carinae present on both margins of each, transverse axis of each cusp base Ṥ 15° (major) or 0° (minor) to labial margin of base; intermediate cusp complete, leans posteriorly, with carinae, reverse compressed (am−pl at base, l−l distally), relative length 1/2–2/3 of principal cusps.
Remarks.—Despite their small size, all three of the teeth appear to be adult, comparable to the smaller teeth in Fig. 6A View Fig . The smaller posterior tooth is nearly round, and even with its stubby prominent cusps, has the appearance of a pancake. The absence of an intermediate cusp and near absence of a central foramen suggests a posterior position in the dental arcade, although the straight principal cusps (as preserved) suggests otherwise. The recumbent cusps would seem to preclude it from being a medial or lateral tooth. There is no evidence that it is deformed, nor is it a germinal tooth. There may be some enclosing matrix that might influence its appearance, but surprisingly, its presence could not be identified with certainty. Because of the apparent attitude of the cusps and an overall lack of detail (probably a diagenetic effect), its identity is questioned.
The larger posterior tooth has some of the same attributes as the smaller tooth, yet they are quite different in appearance. The principal cusps may have been of equal size, and apparently leaned posteriorly. Two or three “microforamina” occupy the position of the central foramen. Both the apical button and basal tubercle may have extremely subdued lingual extensions. Matrix is present but does not contribute to problems of identification; rather, this results from the overall worn appearance and lack of information about the principal cusps.
The posterolateral tooth has a robust crown relative to its thin base. The principal cusps are unusually broad near their base, which contributes to the robust appearance. This, along with a greater than normal base length:width ratio of 1.29 compared to the mean ratio of 0.97 ( Fig. 6A View Fig ), is cause to question its identity. Stratigraphic and geographic range.—Lower Pennsylvanian, southeastern Arizona, USA.
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