In paleontological research, fossil specimens have to be prepared in a laboratory where rock matrixes are removed to fully expose the fossil for observation. This can be done by manual or mechanical preparation, or by acid treatment of specimens. However, these traditional means of specimen preparation are not only unable to fully reveal three-dimensional structures of the fossil, but often cause irretrievable damage on the specimen. If enough number of specimens are available, serial-sectioning technique can be employed to examine the interior structures of fossil specimens.3 Nevertheless, the lost part between thin sections also precludes the recovery of a complete morphology of the specimen.
High-resolution X-ray tomography (high-resolution micro-CT or μCT) features as an established technique that is capable of acquiring the complete three-dimensional morphology of a physical object via X-rays within a short time period. Obviously, μCT technique bears several advantages (high resolution, high efficiency and non-destructive detection) over the laborious and tedious mechanical preparation or serial-sectioning techniques, and thus it has been extensively used to investigate a number of key transitional groups of vertebrates, including sarcopterygian Eusthenopteron,4–5 basal tetrapod Ichthyostega,6 pelobatid frog Prospea,7 stem snake Dinilysia,8 ctenochasmatid pterosaur Liaodactylus,9 tyrannosauroid dinosaur Alioramus,10 early bird Confuciusornis11 and early mammal Vilevolodon.12 μCT technique not only facilitates the observation and measurement of specimens, but also allows investigators to conduct functional morphological studies based on digital models, such as biomechanical analysis of the limb mobility of the early tetrapod Ichthyostega.6 Furthermore, three-dimensional digital models can be printed to produce physical casts, which are ideal for both research and museum exhibition.
This paper provides the μCT source data of a primitive salamandroid Qinglongtriton gangouensis. Salamanders are a group of tailed amphibians, including three suborders: Cryptobranchoidea (70 species, 11 genera, 2 families), Salamandroidea (633 species, 55 genera, 7 families) and Sirenoidea (4 species, 2 genera, 1 family). Salamanders are classified in the subclass Lissamphibia along with frogs and caecilians.13 Previous studies based on molecular data show that salamanders are an ancient lineage, originated about 262.5~357.0 million years ago.14–15 Since 1990s, tens of thousands of salamander specimens have been found from the Mesozoic strata in northern Hebei Province, western Liaoning Province and southeastern Inner Mongolia, China. These fossils are remarkably well preserved and show quite a rich taxonomic diversity. To date, 10 species in 8 genera have been identified as cryptobranchoids and 2 species in 2 genera as salamandroids.16–18 This paper, our recent publication of the salamandroid Qinglongtriton, represents the first application of μCT and 3D printing in the research of fossil salamanders from China.17 By using these new techniques, we were able to provide a more thorough morphological account of this significant Jurassic fossil taxon than previous studies on fossil salamanders from China, and hence shed new lights on the early evolution of Salamandroidea.17
Publication of high-quality μCT source data in paleontological research makes an easy way for researchers to share digital models of important fossil specimens in a global scale. We realize that several online libraries, like Dryad or DigiMorph, have already archived the μCT source data and 2D and 3D visualizations of several important fossil specimens. Therefore, this paper provides the μCT source data of the holotype (PKUP V0226) and two referred specimens (PKUP V0228, PKUP V0254) of the early salamandroid Qinglongtriton gangouensis from the Upper Jurassic Tiaojishan Formation of Hebei Province, China. This paper is also supplemented with a 3D printable stl file of the upper body skeleton of the holotype (PKUP V0226), as well as images and videos displaying the reconstructed skeleton of the three specimens.