In search of lost time: Recovering missing stratigraphical data from fossil marine reptile specimens using micropalaeontological analyses

Abstract

Many museum and university collections contain fossil marine reptile specimens that have no provenance data associated with them, particularly those collected in the 19th and early 20th centuries. This may be because the information was never known to the museum or because the data have since been lost. Moreover, data that are associated with a specimen may have been assumed historically rather than verified and it is known that collectors, donors or sellers of specimens have sometimes been deliberately secretive or even misleading about the actual provenance of the fossils. If invertebrate macrofossils can be identified in the host matrix of the marine reptile specimen these can sometimes offer clues as to the stratigraphical origin of the specimen, but these instances are rare. Micropalaeontological analyses, however, can be undertaken on relatively small amounts of matrix associated with a specimen to attempt the recovery of lost data or confirm or reject assumed provenance details. Permission has been obtained to take small samples (as little as five grams) of host matrix from the rear of several ichthyosaur specimens during recent conservation projects where the provenance of the specimen was either totally unknown or was in doubt. These samples were analysed for their calcareous microfossil content, including ostracods and foraminifera. It was found that well-cemented limestones contained little or no recoverable material but softer mudstones have sometimes yielded very useful assemblages allowing specific biozones to be attributed to the host specimens, successfully recovering lost data and making the specimens much more useful scientifically. Even when the assemblage of microfauna is found to be poor or absent, some information about the sedimentary conditions of the preservational environment can often be ascertained from the micropalaeontological residues.