A LAST SUPPER FROM THE LATE ORDOVICIAN: A CRINOIDIVOROUS POLYPLACOPHORAN FROM SCOTLAND

Specimens of the polyplacophoran mollusk ‘Helminthochiton’ thraivensis Reed from the Upper Ordovician of southwest Scotland provide rare examples of complete valve-series preserved in near life-position, albeit as external molds. Application of high resolution X-ray MicroTomography (XMT) to one such specimen has revealed the exceptional preservation of its last meal, which included elements of a crinoid column, in its intestine. The interaction was either predatory or scavenging; extant chitons are not known to be crinoidivorous.

This is the earliest definite record of predation/scavenging on crinoids in the fossil record. It is also the first indication that the broad axial canal of primitive crinoids may have contained nutritious tissues. The predatory/scavenging habit of H. thraivensis is consistent with its inferred phylogenetic position as a stem-group aplacophoran and provides new data suggesting an origin of carnivory early in the evolution of this clade.