Radioporacanthodes Vergoossen, 1999
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https://doi.org/ 10.5281/zenodo.5376020 |
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persistent identifier |
https://treatment.plazi.org/id/020087A6-3241-311A-FD17-FDA74AF8FDC2 |
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treatment provided by |
Marcus |
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scientific name |
Radioporacanthodes Vergoossen, 1999 |
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Genus Radioporacanthodes Vergoossen, 1999
TYPE SPECIES. — Poracanthodes porosus Brotzen, 1934 .
Radioporacanthodes porosus ( Brotzen, 1934) HOLOTYPE. — Scale figured by Brotzen (1934: pl. 3, fig. 2) from a Lower Devonian erratic boulder (Bey. 36), lowlands of north Germany. Type material appears to be lost.
DIAGNOSIS (summarized from Vergoossen 1999b). — Average to large porosiform scales; rhombic horizontal crown that is longer than wide, a round or angular anterior crown edge which is smooth or with 12 or more short radial ribs, and a medial sulcus; pore canal system developed in posterior half of crown, with up to six subparallel rows of pores; deep neck; deep, concave base.
MATERIAL EXAMINED ( Table 1). — One scale in sample C864, four scales including MMMC 02553 ( Fig. 4E, F View FIG ) in C923 and three scales including MMMC 02564 ( Fig. 3H, I View FIG ) in C925.
DESCRIPTION ( FIGS 3H, I View FIG ; 4E, F View FIG )
The scales are mostly relatively large, being up to 1.0 mm wide. The crown has a smooth anterior margin with a medial sulcus. None of the scales are preserved whole, with most having the posterior crown broken off. MMMC02564 ( Fig. 3H, I View FIG ) has six radial canals running back from the centre of the crown, parallel to the broken edges of the postero-lateral sides. The neck is deeply concave all round, with a sharp rim separating it from the deep, rounded base. The smaller scale MMMC02553 ( Fig. 4E, F View FIG ) is much flatter, with a smooth crown having a medial sulcus on the anterior edge. Although the posterior crown has broken off, thus removing evidence of crown pores, the openings of six radial canals are visible high on the posterior neck.
REMARKS
The taxon R. porosus s.s. has been recorded from Pridoli-Lochkovian deposits in the Baltic, northern Germany, Great Britain (Vergoossen 1999b) and possibly Arctic Canada ( Burrow et al. 1999) and Greenland ( Blom 1999). Vergoossen (1999b) revised the taxonomy of the poracanthodidid acanthodians, excluding many of the poracanthodidid variants which have been assigned to “ Poracanthodes porosus ” over the years (e.g., those listed by Lehman 1937; Märss 1986; Valiukevic˘ius 1998). The Australian scales conform to the smoothcrowned diagnostic type for R. porosus s.s.; some resemble a specimen from the Cape Phillips Formation (Late Silurian, Pridoli), Cornwallis Island, Arctic Canada which Burrow et al. (1999: fig. 6C) assigned to Poracanthodes sp. cf. P. porosus . Although MMMC02553 has a low neck and base, which would exclude it from R. porosus s.s. by Vergoossen’s (1999b) diagnostic criteria, it is presumed such dorso-ventrally flattened scales are a rarer, nontypical scale form as has been noted in other taxa (e.g., Trundlelepis cervicostulata Burrow, 1997 ).
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