Acanthodidae indet, Huxley, 1861

Acanthodidae indet .

( Fig. 3)

MATERIAL. — Eight partially preserved fin spines ( MHNT. PAL. 2023.9.31 [ Fig. 3A]; MHNT.PAL.2023.9.32 , MHNT. PAL.2023.9.33 [ Fig. 3B]; MHNT.PAL.2023.9.34 [ Fig. 3C]; MHNT.PAL.2023.9.35 [ Fig. 3D]; MHNT.PAL.2023.9.36 , MHNT.PAL.2023.9.37 and MHNT.PAL.2023.9.51 )

DESCRIPTION

These spines are all slightly curved, more or less pointed at their distal end (see below) and have a smooth surface. All have a groove along their lateral sides and none bear denticles. Their sizes and morphologies vary slightly in terms of total length, curvature, shape of the apex and width of the entire spine.Two morphotypes can be distinguished: the first, with specimens MHNT.PAL. 2023.9.31, MHNT.PAL.2023.9.32, MHNT.PAL.2023.9.33, MHNT.PAL.2023.9.36, MHNT. PAL.2023.9.37 and MHNT.PAL.2023.9.51 corresponds to large spines with a total length above 30 mm, a width of 3 to 5 mm along the entire length, and a rather rounded distal end. The second morphotype, with specimens MHNT. PAL.2023.9.34 and MHNT.PAL.2023.9.35, corresponds to smaller and finer spines with a total length below 10 mm, a width of less than 1 mm and a pointed distal end.

COMPARISONS

The spines herein described are long, slender, slightly curved and grooved on each lateral side, making them attributable to the Acanthodidae (e.g. Beznosov 2009). Isolated acanthodian fin spines found in the Carboniferous basins of France have traditionally been referred to the genus Acanthodes (e.g. Heyler 1969). However, acanthodid fin spines are generally devoid of diagnostic features at the generic level (e.g. Zidek 1976). The presence of different morphotypes may correspond to variations between pectoral, anal and dorsal fin spines, although these are poorly known in acanthodids. Despite their number, the acanthodian fin spines from La Découverte remain isolated and, in the absence of more complete associated skeletal remains, they cannot be assigned to a more precise taxon. Pending more discovery, we hereby refer these specimens to the open nomenclature Acanthodidae indet.