FOSSIL BRACHIOPOD PRESERVATION: THE USE OF MODERN TECHNOLOGY REVEALS ANCIENT SECRETS

Brachiopods, found in the fossil record for over 500 million years, have been an essential tool for biostratigraphic, paleogeographic, and paleoecologic interpretation. When investigating brachiopods in the above context the first step is, without doubt, determination of taxonomic assignment. This determination is heavily dependent on the quality of preservation of the specimens. Preservation of molds allows a detailed study of micro-ornamentation and muscle and visceral impressions (e.g. gonoglyphs) that are almost impossible to observe on articulated shells and in transverse and longitudinal serial sections. Serial sections however, allow us to study the brachidium and crura that are rarely preserved on internal molds. Silicification may preserve all morphologic information (hard part), however weak silicification often destroys the shell structure or, the shell itself may be incompletely silicified. CT scans are only useful if there is enough contrast between shell material and sediment matrix (e.g. silicified or pyritized shells in a calcareous matrix). Different types of preservation will yield varying amounts of morphologic data. It is difficult to compare taxa that are preserved in different ways if there are missing data. How can we determine whether articulated shells from one locality represent the same or a different species based on external or internal molds from another, almost coeval but geographically separate locality? Here we present examples of Phanerozoic brachiopods preserved as molds, articulated shells and free valves, and illustrate how the use of modern reconstruction techniques allows a direct comparison between specimens.