Orthacanthus sp.
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publication ID |
https://doi.org/ 10.4202/app.2008.0051 |
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persistent identifier |
https://treatment.plazi.org/id/03802969-2239-8051-AE53-77F3FE3F98A1 |
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treatment provided by |
Felipe |
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scientific name |
Orthacanthus sp. |
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Material.— UAPL 23495.
Description.—Tooth fragments: two incomplete teeth and eight isolated cusps.
Remarks.—There is little doubt about the identity of the five larger isolated cusps, as they possess carinae but no cristae. Three much smaller cusps could belong to other xenacanth taxa in the Swisshelm fauna, but lack cristae as well as carinae. One of the incomplete teeth consists of a partial base with part of a principal cusp and perhaps most of an intermediate cusp. The other incomplete tooth is represented by a partial base and may be a germinal tooth.
Fig. 11 View Fig .
Material.— UAPL 23496, one tooth; UAPL 23401, one tooth; and UAPL 23400, germinal tooth.
Description. —Tooth ( UAPL 23496) with 1.43 mm (am−pl) × 0.96 mm (l−l) base with a veneer of matrix; central foramen?present; strongly am−pl oval apical button isolated from cusps, with a very small lingual extension producing a distinct protuberance on lingual margin of base; basal tubercle?small, possibly with a lingual extension; aboral foramina indeterminate, Ẑ two prominent oral foramina; principal cusps of?equal size shattered near base, carinae may have been present; one intermediate cusp shattered near base.
UAPL 23401, tooth with apical button in contact with principal cusps; base with about 2 mm dimensions; both principal cusps lean posteriorly; presence of central foramen not confirmed; in matrix.
Small germinal tooth ( UAPL 23400, Fig. 11 View Fig ). Base 1.40 mm (am−pl) × 0.68 mm (l−l); basal tubercle not centered on labial margin and lacks lingual extension; aboral surface of base deeply concave. Intermediate cusp and apical button absent; central foramen present.
Remarks.—Both the anterior and posterior ends of the base of UAPL 23496 markedly extend beyond the margins of the cusps. Its strongly oval base (length:width ratio = 1.49) is quite unlike any Orthacanthus donnelljohnsi sp. nov. tooth, more so for Triodus . A lack of cristae on the labial margin of the base precludes Bransonella as a possibility.
UAPL 23401 is unusual because typical Orthacanthus teeth possess an apical button that is isolated from the cusps (Johnson 1999: 223). Otherwise, it appears to be normal, although the presence of matrix prevents determination of other characters that might confirm its identity.
UAPL 23400 ( Fig. 11 View Fig ) is more anomalous than usual. It has an extreme length:width ratio of 2.06; its position in the dental arcade is unknown. The offset basal tubercle and deeply concave base ( Fig. 11B View Fig ) suggest the possibility that it is malformed as well as being germinal. Whether it represents an adult or juvenile tooth is unknown. Its identity is uncertain because of its extreme length:width ratio, as well as its other abnormal attributes.
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