Phylogenetic value of jaw elements of lacertid lizards (Squamata: Lacertoidea): a case study with Oligocene material from France

Abstract

Several extinct species are known from the family Lacertidae, but due to poor preservation, many of them are based on single bones. Here, we compare phylogenetic signals of disarticulated premaxillae, maxillae and dentaries of lacertids from four French Oligocene localities (Coderet, La Colombière, Roqueprune 2, Mas de Got B). We identified five morphotypes among the premaxillae, six among the maxillae, and ten among the dentaries. These morphotypes were scored as individual taxa per locality into three separate character matrices with the same 246 characters, one matrix for each jaw element. Subsequently, the phylogenetic position of the morphotypes was tested using maximum parsimony. The consensus trees with the dentaries and the maxillae found a large polytomy including all taxa except the outgroup taxon Gekko gecko. The consensus tree with the premaxillae showed a considerably more resolved topology but found all morphotype taxa outside Lacertidae. In a second step, we compared the constitution of our three datasets and the morphotype taxa. Our results suggest that a combination of convergent characters and missing data led to the outgroup position of the premaxilla morphotype taxa. The poor resolution of the maxillae strict consensus is likely a consequence of their fragmentary preservation. For the dentaries, a high amount of missing data due to the high number of morphotype taxa most likely caused the poor tree resolution. Indeed, tests with fewer morphotypes found tree resolutions comparable to the premaxilla data. When linking the morphotypes, five possible lacertid "species" were found. Comparison with already known French Oligocene lacertid species points to a slightly higher species richness of Lacertidae at that time than known before. Reliable species classification based on phylogeny only seems possible when combining the jaw elements or in association with other cranial and postcranial material, putting some doubt on species identifications based on single bones.