Osteology, fossil record and palaeodiversity of the European lizards

Abstract

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 genus Lacerta.

The challenges and potential utility of phenotypic specimen-level phylogeny based on maximum parsimony

“…Additionally, Kimura et al (2016) demonstrated that the appearance of diagnostic features 869 is delayed in respect to lineage splitting in murid mammals. High intraspecific variability among 870 osteological features has also been shown in the lacertid lizard Lacerta (Villa et al 2017), where no 871 single trait could be identified as a unique, unambiguous autapomorphy of a species; rather, only 872 combinations of traits were found to be species-specific. 873…”

“…2017), and also extended implied weighting seemed to work well under certain circumstances when analysing specimen-level data in lizards (Villa et al . 2017). One reason for these discrepant conclusions could be that the modelled phylogenies did not accurately represent a real distribution of homoplasy within a morphological dataset (Goloboff et al .…”

“…Additional tests with real data sets (such as that of Villa et al . 2017) and a higher range of downweighting functions will be needed to compare the performance of different weighting methods, including extended implied weighting, in order to resolve this debate.…”

“…(such as that of Villa et al 2017), and a higher range of downweighting functions will be needed to 631 compare performance of different weighting methods, including extended implied weighting in 632 order to resolve this debate. 633 Tschopp et al (2015) noted that using an implied weighting strategy was useful to address 634 the potentially misleading ontogenetically variable characters, because the ontogenetic changes add 635 variability to these characters, which therefore have a higher homoplastic rate, and so are 636 downweighted more strongly than less variable ones.…”

Trapped in a roman well: amphibians and reptiles from Tenuta Zuccarello near Marcon, Venice, Italy

“…Smaller remains of lacertids, whose identification is notoriously tricky (Villa et al 2017), have been attributed only to indeterminate members of the family. They could represent another smaller species, but also juveniles of Lacerta gr.…”