A partial articulated acanthodian from the Silurian of New Brunswick, Canada

Abstract

Vertebrates preserved in calcareous concretions collected from Silurian marginal-marine deposits near Nerepis, southern New Brunswick include agnathan thelodonts, a heterostracan, and possibly an anaspid, as well as spines and scales from an acanthodian (the only jawed fish remains). Several incomplete specimens of acanthodians, all determined as the same taxon Nerepisacanthus denisoni nov. gen. et sp., are described based on material identified in several museum collections. The fish-bearing nodules are from the Silurian Cunningham Creek Formation, which has been dated from ?late Llandovery (Telychian) – Ludlow (Ludlovian). The new species is only the second undisputed pre-Devonian acanthodian taxon known from articulated, although incomplete, specimens. N. denisoni has robust flank scales with a smooth crown bearing short subparallel ridges along the anterior edge, plus flatter scales with a crown formed of elongate, curved, areal-growth ridges, anterior to the pectoral region. The anterior dorsal fin spine is long, slightly curved and bears up to seven smooth longitudinal ridges of varying width on each side. The perichondrally ossified scapula is thin-walled and probably has a U-shaped cross section. “Dentition” cones and small denticles are preserved in the branchial or pharyngeal region. Although elements indisputably identifiable as dentigerous jaw bones were not found in the specimens, N. denisoni appears most closely related to the Early Devonian ischnacanthiform Acritolepis and is tentatively assigned to the family Acritolepidae Valiukevičius and Burrow.