Allometric patterns in phrynosomatid lizards and the implications for reconstructing body size for fossils

• Published in: Evolutionary ecology 2022-08, Vol.36 (4), p.561-590
• Main Authors: Knight, Jaylin A., Ledesma, David T., Kemp, Melissa E.
• Format: Article
• Language: English
• Subjects: Allometry; Analysis; Animal Ecology; Biological evolution; Biomedical and Life Sciences; Body size; Bones; Case studies; Divergence; Domestic relations; Ecology; Evolution; Evolutionary Biology; Fossils; Life history; Life Sciences; Lizards; Ontogeny; Original Paper; Plant Sciences; Scaling; Species; Taxa; Taxonomy
• ISSN: 0269-7653; 1573-8477
• DOI: 10.1007/s10682-022-10186-5

Body size is an important life history trait that for fossils can be reconstructed by utilizing scaling relationships between body size and measurements on isolated bones from extant taxa. Allometry, which describes the scaling relationship between such a measurement and body size, has traditionally been thought of as constrained, meaning that evolutionary allometries should follow the same trajectories as ontogenetic and static allometries. However, if allometries are evolving it may be difficult to accurately estimate body size for extinct taxa or fossils that cannot be identified to low taxonomic levels. Knowing the degree to which the allometric relationships of features are evolutionarily constrained therefore has implications for studying the fossil record and can also provide insight into morphological evolution. We use phrynosomatid lizards as a case study for investigating scaling relationships at different taxonomic levels. We examined scaling relationships between body size, represented as snout-vent length (SVL), and 15 skeletal measurements taken from 188 phrynosomatid lizards with 30 species represented. For each measurement, we developed species-level, genus-level, subfamily-level, and family-level linear models. We used these models to predict SVL in cross-validation tests and determine which models and measurements produced the most accurate body size predictions. Generally, predictions from congeneric species accurately reconstructed body size, but some measurements also exhibited conserved scaling relationships across phrynosomatids and appear to serve as good family-wide predictors for body size. We found that static allometries are more similar to evolutionary allometries at the genus-level than to family-level evolutionary allometries. Differences between evolutionary allometries at the genus and family-level appear to be driven by Phrynosoma, as measurements on several cranioskeletal elements are highly divergent. Our work sets a foundation for understanding allometric relationships across Phrynosomatidae and provides a framework for examining trends in body size based on evidence from the fossil record.