Fossilized soft tissues in a Silurian platyceratid gastropod

Abstract

Gastropod shells are common in the fossil record, but their fossil soft tissues are almost unknown, and have not been reported previously from the Palaeozoic. Here, we describe a Silurian (approx. 425 Myr) platyceratid gastropod from the Herefordshire Lagerstätte that preserves the oldest soft tissues yet reported from an undoubted crown-group mollusc. The digestive system is preserved in detail, and morphological data on the gonads, digestive gland, pedal muscle, radula, mouth and foot are also available. The specimen is preserved three-dimensionally, and has been reconstructed digitally following serial grinding. Platyceratids are often found attached to echinoderms, and have been interpreted as either commensal coprophages or kleptoparasites. The new data provide support for an attached mode of life, and are suggestive of a coprophagous feeding strategy. The affinities of the platyceratids are uncertain; they have been compared to both the patellogastropods and the neritopsines. Analysis of the new material suggests that a patellogastropod affinity is the more plausible of these hypotheses.

Platyceratid gastropods - stem group of patellogastropods, neritimorphs or something else?

“…Taken together, the interpretation of platyceratoid gastropods as the stem group of patellogastropods based on sharing of the same shell microstructure is in conflict with the pattern of their early shell ontogeny. Two years ago Sutton et al (2006) reported the discovery of an unusually well preserved gastropod with fossilized soft tissues from the Lower Silurian (Wenlock Series) Herefordshire Lagerstätte of England. This gastropod was assigned to the Platyceratidae on the basis of its simple subcircular aperture, trochiform shell and the absence of ornamentation.…”

“…Its study has revealed detailed data on the digestive system as well as morphological data on the gonads, digestive gland, pedal muscle, radula, mouth and foot. According to Sutton et al (2006) the digestive system is the most informative phylogenetically of all the preserved soft-tissue characters. These anatomical data together with the absence of the operculum were interpreted as suggesting that platyceratids were symbiotic rather than predatory on their hosts.…”

“…These anatomical data together with the absence of the operculum were interpreted as suggesting that platyceratids were symbiotic rather than predatory on their hosts. However, a more important conclusion made by Sutton et al (2006) is that anatomical characters of their Platyceras? sp.…”

“…Sutton (pers. comm., 2008) we had the chance to examine in detail the apical view of a shell from the Herefordshire Lagerstätte (Sutton et al 2006, fig. 1f).…”

“…Unfortunately no traces of protoconch morphology were observed. The discovery made by Sutton et al (2006) is important for the interpretation of the patellogastropod phylogeny (the Silurian gastropod from the Herefordshire Lagerstätte may represent a coiled ancestor of the Patellogastropoda), but cannot be used as evidence for platyceratid and patellogastropod affinity. …”