Abstract
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.
Highlights
In recent years there has been an increase in the use of virtual palaeontology, in particular in three-dimensional reconstructions based on tomographies obtained from the techniques of computed axial tomography (CAT) or micro-computed tomography, in palaeontological studies [1,2,3]
The D. glyphodon material comes from the Gran Dolina site (TD); the B. fissidens material comes from the site of Sima del Elefante (TE); all the fossil material is stored in the Museo de Ciencias Naturales de la Universidad de Zaragoza [41]
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
Summary
In recent years there has been an increase in the use of virtual palaeontology, in particular in three-dimensional reconstructions based on tomographies obtained from the techniques of computed axial tomography (CAT) or micro-computed tomography (microCT), in palaeontological studies [1,2,3] This has occurred due to the high quantity and variety of applications derived from this type of reconstruction, including the possibility of extracting the fossil data from the rock that contains the fossil, sharing this information, studying the interior cavities, structures and materials of the fossil, characterizing fossils in 3D, retrodeforming fossils that have undergone plastic deformation, digitally reconstructing their palaeobiology, testing the movements and insertions of bones, and performing functional analyses using reverse engineering tools such as finite element analysis or hydrodynamic studies It is because work with 3D virtual models can be at any scale, so the advantages in handling and cleaning are equal for all sizes of fossils, as long as all relevant specimen features are above the lower resolution threshold.
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