Date Published: March 20, 2019
Publisher: Public Library of Science
Author(s): Raquel Moya-Costa, Gloria Cuenca-Bescós, Blanca Bauluz, Sergi Lozano.
We have developed a protocol for reconstructing 3D models of the skulls of extinct species of small mammals. For the first time, the reconstruction uses fragments of fossils from a mixture of different specimens and from related extant species. We use free software and commercial computers to make the process reproducible and usable for the scientific community. We present a semi-quantitative protocol to face the problem of making 3D reconstructions of fossil species that are incomplete in the fossil record and/or represented by a mixture of different individuals, as usually occurs with small vertebrates. Therefore this approach is useful when no complete skull is available. The protocol combines the use of microCT scan technology with a subsequent computer treatment using different software tools for 3D reconstruction from microCT and 3D design and printing (e.g. Fiji, SPIERS, Meshlab, Meshmixer) in a defined order. This kind of free and relatively simple software, plus the detailed description, makes this protocol practicable for researchers who do not necessarily have great deal of experience in working with 3D. As an example, we have performed virtual reconstructions of the skulls of two species of insectivore small mammals (Eulipotyphla): Beremendia fissidens and Dolinasorex glyphodon. The resulting skulls, plus models of the extant shrews Blarina brevicauda, Neomys fodiens, Crocidura russula and Sorex coronatus, make it possible to compare characteristics that can only be observed by means of microCT 3D reconstructions, and given the characteristics of the material, using this protocol. Among the characters we can compare are the position of the mandibles, the spatial relations among all the teeth, the shape of the snout and, in general, all parameters related with the anatomy of the rostrum. Moreover, these reconstructions can be used in different types of context: for anatomical purposes, especially to see internal features or characteristics at whole-skull scale, for bioengineering, animation, or other techniques that need a digital model.
The protocol described in the present paper have made it possible, for the first time, to reconstruct in 3D the anatomy of two small mammals that are systematically incomplete or fragmented in the fossil record. The 3D reconstruction of skulls belonging to extant and fossil shrews has enabled us to arrange the mandibles in their anatomical position, to orient them and facilitate comparisons among them, and to compare their internal structures. At present there is no other way of producing a complete reconstruction of fragmented small vertebrates with pieces from different individuals, except by means of 2D reconstructions using palaeoart. The advantages of our 3D models are firstly that with each step the insertion of each scaled element and the occlusion of teeth can be tested, and secondly that the final models allow researchers to do anything that is possible with a normal 3D model, such as rotating and measuring elements in any direction, seeing the interior without affecting the original pieces, and producing animations.