Paper No. 2
Presentation Time: 8:20 AM
3D RECONSTRUCTIONS OF INTERNAL ARTICULATED BRACHIOPOD SHELLS: USEFUL TOOL OR ONLY A FANCY COMPUTER APPLICATION? A CASE STUDY OF SEPTIRHYNCHONELLID BRACHIOPODS
Brachiopods represent one of the major fossil groups used in biostratigraphic and paleobiogeographic research; however, the first step when working with brachiopods is the accurate taxonomic identification that is based, in most cases, on internal shell morphology. Whereas Paleozoic brachiopods are often preserved as isolated shells, Mesozoic brachiopods are mainly preserved as articulated shells. The fact that they are characterized by strong homeomorphy makes identification difficult and, in the past, serial sections were the only way to accurately examine and identify their internal structures. Recently, the use of CT scans and 3D reconstructions of the shells’ images has become a common and very useful method, especially for vertebrate paleontologists. Without doubt, a good high resolution 3D reconstruction is better than a set of pictures of ground and etched surfaces. Most of the preserved shells, however, do not show high contrast between shell material and matrix and, as a result, the CT images are not suitable; time consuming serial sections remain the most practical procedure for studying the internal shell. The digitalization of ground and etched surfaces followed by 3D reconstruction is a compromise that solves the contrast problem. However, the procedure is long and distances between manually prepared sections cannot be less than 20 microns. Thus, the question arises as to whether this method is really suitable for 3D reconstruction. We discuss this problem using septirhynchonellid brachiopods from the Middle Jurassic of France, Israel, and Jordan as an example. By studying isolated silicified shells, articulated calcareous shells, peels, and ground and etched surfaces in collections, together with a comparison of 3D reconstructions and isolated shells, two genera within this group of strongly dorsibiconvex rhynchonellids could be identified. Our interpretation is confirmed by morphometric analyses of the external shells.