Abstract
The capability of palaeontologists to identify fossil remains of a particular group of vertebrates strongly depends on the knowledge they have of its comparative osteology and on the actual presence of diagnostic differences among the considered taxa. This could have a relevant influence on the study of palaeodiversity, since a low recognisability causes a loss of data when trying to reconstruct the history of taxa that lived on Earth in the past. Currently, more than 6000 extant species of lizards and worm lizards are known, and new ones continue to be discovered, mainly based on molecular data. But are we able to recognise this high diversity using osteology? As far as European taxa are concerned, the osteological recognisability of non-snake squamates is very low: only 31% of the extant European taxa can be identified based on their skeletal morphology. This is balanced partially by the fact that most recognisable taxa have been actually recognised in the fossil record, suggesting that the lost data are mainly due to the scarce knowledge of the comparative osteology of these reptiles and less influenced by other biases, such as taphonomic or collection biases. In this context, specimen-level phylogenetic analysis has proved to be a useful tool to identify diagnostic combinations of osteological features, at least for lacertid species, as evidenced by a case study focused on the genusLacerta.
Highlights
IntroductionNon-snake squamates (i.e., lizards and worm lizards) exist since at least the MiddleJurassic (Rage, 2013), and are represented by more than 6000 extant species worldwide (Uetz and Hošek, 2016) and a number of extinct taxa (for a summary of extinct species see the dated review of Estes, 1983, and Böhme and Ilg, 2003)
Non-snake squamates exist since at least the MiddleJurassic (Rage, 2013), and are represented by more than 6000 extant species worldwide (Uetz and Hošek, 2016) and a number of extinct taxa
The included species correspond to the European amphibians and reptiles reported by Sillero et al (2014), plus the lizards and worm lizards living on the Greek islands along the coast of Asiatic Turkey as reported by Speybroeck et al (2016)
Summary
Non-snake squamates (i.e., lizards and worm lizards) exist since at least the MiddleJurassic (Rage, 2013), and are represented by more than 6000 extant species worldwide (Uetz and Hošek, 2016) and a number of extinct taxa (for a summary of extinct species see the dated review of Estes, 1983, and Böhme and Ilg, 2003). Succinilacerta succinea (Boulenger, 1917) or those recently described by Daza et al., 2016), vertebrate palaeontologists are mostly restricted to osteological features to identify fossil remains and study palaeodiversity. This makes the task of palaeoherpetologists much more complex and error-prone than that of neoherpetologists, given that it strongly depends on the degree of knowledge of the comparative osteology of the considered group and on the actual presence of diagnostic differences among the taxa. We here try to quantify the current osteological recognisability of the extant European non-snake squamates, in order to evaluate to what degree it affects our ability to comprehend the past diversity of these reptiles in the continent. We try to assess the utility of phylogenetic analyses to identify diagnostic osteological features for lizards, and lacertids in particular
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