Protacrodontoidea Zangerl, 1981

Ginter, Michał, 2002, Chondrichthyan fauna of the Frasnian-Famennian boundary beds in Poland, Acta Palaeontologica Polonica 47 (2), pp. 329-338 : 334-336

Superfamily Protacrodontoidea Zangerl, 1981 Genus Protacrodus Jaekel, 1921

Type species: Protacrodus vetustus Jaekel, 1921 .

Protacrodus vetustus Jaekel, 1921

Fig. 6 .

Protacrodus vetustus Jaekel ; Gross 1938: 131–141, figs. 3–5, pl. 2.

Protacrodus vetustus Jaekel ; Glikman 1964: fig. 20.

Protacrodus vetustus Jaekel ; Zangerl 1981: 62, figs. 64, 65.

Protacrodus cf. vetustus Jaekel ; Ginter 1991: 75, pl. 8: 5.

Protacrodus cf. vetustus Jaekel ; Ginter 1995: figs. 2B [?], 4B.

Protacrodus cf. vetustus Jaekel ; Ginter and Ivanov 2000: pl. 1F.

Material.—Six teeth from the Holy Cross Mts: one specimen from Kowala (sample Ko−SF, Pa. linguiformis Zone ), two specimens from Wietrznia (samples W−37, Middle Pa. crepida , W−47, Late Pa. triangularis Zone ), two specimens from Jabłonna (sample J−IIIs, Middle Pa. triangularis Zone ), and one specimen from Miedzianka (sample Md−I/1, Pa. crepida Zone ). Ginter (1995: fig. 2B) figured a Protacrodus tooth, allegedly the only specimen of this genus found thus far from Płucki (sample P−1, Pa. linguiformis Zone ). Actually, that specimen might have come from some other sample and, therefore, the occurrence of protacrodonts in Płucki remains uncertain.

Description.—Teeth of this form have pyramidal crowns, with the lower parts of the cusps fused together. The median cusp is subcircular in cross section and bears strong, straight or slightly wavy ridges, joining at the tip. The lateral cusps, usually three on each side, are smaller than the median cusp and generally similar in form. However, in some specimens they can be slightly labio−lingually compressed. There are also some differences in the relative height of the lateral cusps: in some forms ( Fig. 6B–D ) the cusps of the second lateral pair are higher than, and in the other, almost equal to those of the first pair.

The teeth have laterally elongated bases, almost without lingual extensions and lacking any articulation devices. Usually a horizontal row of irregular, large pores perforates the lingual and labial faces of the base, and another row of smaller, rounded foramina goes a little higher, along the crown−base interface (the best visible in Fig. 6D , left side). Possibly, the lower row of pores was used by the nutritive vessels connecting the teeth in a tooth−whorl, and the vessels going directly from the covering soft tissue entered a tooth through the upper row of pores.

There are fragments of protacrodont tooth−whorls in the material from the Miedzianka Hill and Jabłonna. In the specimen from Miedzianka ( Fig. 6A ), bases of three teeth are fused together, with only very little overlapping. The teeth differ in size: the smallest (presumably the oldest) tooth is about 3/4 as high and wide as the largest (youngest) one. This suggests that the tooth replacement in P. vetustus was rather slow, and that these three teeth, or probably even more, were functional for crushing at the same time.

Remarks.—Protacrodont teeth described above (especially IGPUW/Ps/4/13, Fig. 6B–D ) are generally similar to the teeth of the holotype of P. vetustus from Bad Wildungen (housed in the Museum für Naturkunde, Humboldt Universität, Berlin), thoroughly described and illustrated by Gross (1938) and then reillustrated by Zangerl (1981: figs. 64, 65). However, the teeth of the type specimen are rather uniform, all of them having conical lateral cusps without any labio−lingual compression. Thus, the teeth which possess slightly flattened lateral cusps are assigned here only tentatively to P. vetustus . Later in the Famennian very similar teeth appear, but with all the cusps compressed, the median cusp included, and bent lingually. I have previously referred to them as P. cf. vetustus (Ginter 2000) , but they probably belong to another species of Protacrodus .

Stratigraphic range in Poland.—Latest Frasnian–early Famennian, Pa. linguiformis – Pa. crepida zones.

Figures

Fig. 6. Protacrodus vetustus Jaekel, 1921. A. Tooth−whorl composed of three teeth, right side incomplete, IGPUW/Ps/1/222, sample Md−I/1, Late Pa. triangularis Zone, occlusal view, × 30. B–D. Large, almost completely preserved tooth, IGPUW/Ps/4/13, sample Ko−SF, Pa. linguiformis Zone, oblique lingual, oblique labial and lingual views, × 17. All SEM micrographs.