fOrder XENACANTHIFORMES. Pleuracanth-type tooth (three cusps of variable size, usually two prominent lateral cusps and a smaller median one). Claspers in male; elongate dorsal fin base; diphycercal or heterocercal tail; two anal fins; cephalic spine; radials of pectorals jointed and ending well before fin margin.
The Lebachacanthidae and Diplodoselachidae are also in this group, with the latter being the stem xenacanthiform (Soler-Gijon, 2004). Ginter (2004) discussed the origin of the xenacanthiforms and discussed the Antarctilamna-Wellerodus group, Diplodus, the possibly related Bransonella, Jalodus, and Phoebodontiformes, and the distant Omalodontiformes.
Family XENACANTHIDAE. Freshwater; Lower Devonian to Triassic.
For example, Orthacanthus, Pleuracanthus, Triodus, and Xenacanthus.
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