A peculiar bored crinoid from Salthill Quarry, Clitheroe, Lancashire (Mississippian; Tournaisian), UK

Abstract

Salthill Quarry, Clitheroe, Lancashire, is a Site of Special Scientific Interest (SSSI) and important for its Mississippian (Tournaisian, Chadian) crinoids. A pluricolumnal, Pentagonocyclicus ? (col.) sp., preserves multiple pits, Oichnus paraboloides Bromley. Pits on one side of the specimen sit atop cyst-like structures and infested the crinoid when it was alive; the protuberances represent a growth reaction. At the time, the column was either upright, pits concentrating on one side presumably in response to current direction, or recumbent (and distal). Pits on the other side engendered no growth reactions; the crinoid was dead and lying on the sea floor when infested. The infestation of the live crinoid must be considered ectoparasitic.

Trace fossils and tropical karst

“…Pits are limited to one side of the specimen only; none occur on the reverse of that shown in Figure 1a. While such a distribution may be explained by palaeoecological criteria (Donovan & Tenny, 2015), it is nonetheless peculiar in such a densely infested specimen. The column shows no other signs of swelling, another feature commonly seen in infested columns.…”

“…Parabolic pits, alias the trace fossil Oichnus paraboloides Bromley, 1981, are a common feature of echinoderm tests in certain parts of the Phanerozoic succession, such as Wenlock (Silurian) and Mississippian (Carboniferous) crinoids and holasteroid echinoids of the chalk (Late Cretaceous; Donovan, 2015; Donovan, Hammond & Tenny, 2015; Donovan & Tenny, 2015; Hammond & Donovan, in press). The Palaeozoic occurrence of O. paraboloides on crinoids has now been extended into the early Permian Period of Timor, southeast Asia.…”