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Johnson/2003Mitt.Mus.NaturkBerl., Geowiss. Reihe 6 (2003) 125-160

 

Nature of the beast (pun intended): taxonomical (systematic) Monograph

 

" Dentitions of Barbclabomia (new genus, Chondrichthyes: Xenacanthiformes) from the Upper Palaeozoic of North America Gary D. Johnson' With 14 figures and 3 tables

recommended, particularly for those interested in xenacanthids, orthacanthids, etc

 

About 5 Mb

Abstract

Barbclabornia luedersensis (Berman, 1970) is defined on the basis of small (2 111117 high) isolated teeth that lack an intermediate cusp. It is known from the Lower Permian and possibly the Upper Pennsylvanian of North America. The two principal cusps are slightly curved orally, nearly parallel, and bear cristae mainly on their distal halves. They are cylindrical but become compressed proximally. The long axis of each cusp base is >45" to the labial margin of the tooth base. The base bears a prominent apical button in contact with the cusps; a central foramen is absent. Fewer than ten foramina occur on the aboral surface of the base, which bears a prominent concave basal tubercle. The shape of the base ranges from somewhat triangular to quadrangular. The cusps are composed of orthodentine covered by hypermineralized pallial dentine; the base is composed of orthodentine but may also contain trabecular dentine. Except for the possible occurrence of symphysial teeth, the dentition is homodont. Barbclabornia cf. B. luedersensis is stratigraphically highest in the known range of the genus and is restricted to the nearly lowermost part of the Clear Fork Group (Artinskian) of Texas. The teeth are similar to B. lztedersensis, but are more robust and have a quadrangular-shaped base. Barbclabornia was large, based on an undescribed palatoquadrate some 45 cm long. It was probably freshwater and is most closely related to Triodus. Key words: Chondrichthyans, Xenacanthiformes, Early Permian, North America.

 

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