How to Render Species Comparable Taxonomic Units Through Deep Time: A Case Study on Intraspecific Osteological Variability in Extant and Extinct Lacertid Lizards

Abstract

Generally, the species is considered to be the only naturally occurring taxon. However, species recognised and defined using different species delimitation criteria cannot readily be compared, impacting studies of biodiversity through Deep Time. This comparability issue is particularly marked when comparing extant with extinct species, because the only available data for species delimitation in fossils is derived from their preserved morphology, which is generally restricted to osteology in vertebrates. Here, we quantify intraspecific, intrageneric, and intergeneric osteological variability in extant species of lacertid lizards using pairwise dissimilarity scores based on a dataset of 253 discrete osteological characters for 99 specimens referred to 24 species. Variability is always significantly lower intraspecifically than between individuals belonging to distinct species of a single genus, which is in turn significantly lower than intergeneric variability. Average values of intraspecific variability and associated standard deviations are consistent (with few exceptions), with an overall average within a species of 0.208 changes per character scored. Application of the same methods to six extinct lacertid species (represented by 40 fossil specimens) revealed that intraspecific osteological variability is inconsistent, which can at least in part be attributed to different researchers having unequal expectations of the skeletal dissimilarity within species units. Such a divergent interpretation of intraspecific and interspecific variability among extant and extinct species reinforces the incomparability of the species unit. Lacertidae is an example where extant species recognised and defined based on a number of delimitation criteria show comparable and consistent intraspecific osteological variability. Here, as well as in equivalent cases, application of those skeletal dissimilarity values to palaeontological species delimitation potentially provides a way to ameliorate inconsistencies created by the use of morphology to define species.

Species delimitation and coexistence in an ancient, depauperate vertebrate clade

“…The species diversity of † Diplurus observed in Lockatong and Boonton Formation assemblages clearly contrasts with the view of coelacanths as a perpetually depauperate lineage (e.g., [ 13 , 18 , 52 ]). Instead, our results underscore the importance of quantitative approaches to species delimitation in the fossil record (e.g., [ 84 ]). In the case of coelacanths, our understanding of the evolutionary history of the total clade might be warped by observations of the evolutionary history of the crown group.…”

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

“…The response of the lacertids to these climatic and environmental changes is of high interest, especially considering the assumed close temporal association with the origin of crown‐group lacertids. However, in order to understand how these climatic changes influenced taxonomic diversity, it is of crucial importance to assess the validity of the species that occurred during that period of time, as well as the methodology that was used to distinguish them at first place (see also Tschopp et al., in review). Here, we test the latter by comparing the phylogenetic signal of three tooth‐bearing jaw elements of lacertid lizards that often were used to distinguish and erect new species from that period: premaxillae, maxillae and dentaries.…”

Morphological and osteological characterization of indigenous domestic chickens (Gallus gallus domesticus): validation of Rensch’s, Bergmann’s and Allen’s rules

“…Osteological studies can potentially differentiate groups of similar species (Tschopp et al, 2022). In domestic animals, they have played an important role in the identification of their wild ancestors.…”