Mammalian skeletal diversity

Complex interactions among genetic, environmental, and phylogenetic mechanisms mediate and shape phenotypic diversity. Ongoing research efforts have largely followed disciplinary boundaries in micro- or macro-evolutionary scopes, genotypic or phenotypic data, and morphometric or biomechanic subdivisions of functional morphology. In this project, we will integrate genetic, biomechanical, ecological, and macroevolutionary approaches of morphological analysis and test hypotheses about the evolutionary drivers of mammalian skeletal diversity. We will first quantify heritability in skeletal traits by constructing a genetic covariance matrix that characterizes skeletal variation in a non-inbred pedigreed mouse population. We will then use the 55+ million year record of carnivoran mammals as our model system to (1) disentangle how genetic additive effects, biomechanics, developmental bias, and allometry influence skeletal diversity, (2) investigate ecomorphological convergence and its effects on evolutionary integration between skeletal systems, and (3) examine how paleoenvironmental changes influenced the tempo and mode of carnivoran skeletal diversity.

The carnivoran skeleton exhibits mosaic evolution, where only the mandible, hindlimb and posterior (i.e. last thoracic and lumbar) vertebrae showed evidence of adaptation towards ecological regimes. In contrast, the remaining skeletal components (i.e., cranium, forelimb, and anterior (cervical and thoracic) vertebrae exhibit clade-specific evolutionary shifts that corresponded well to carnivoran clades. We hypothesized that the decoupled evolution of individual skeletal components may have led to the origination of distinct adaptive zones and morphologies among extant carnivoran families that reflect phylogenetic hierarchies.

Law CJ, Hlusko LJ, & Tseng ZJ. 2024. Uncovering the mosaic evolution of the carnivoran skeletal system. Biology Letters. 20:20230526. doi.org/10.1098/rsbl.2023.0526

Morphological proxies of function derived from skeletal regions exhibit trade-offs and covariation across their performance surfaces, particularly in the appendicular and axial skeletons. These functional trade-offs and covariation correspond as adaptations to different adaptive landscapes when optimized by various factors including phylogeny, dietary ecology, and, in particular, locomotor mode. We also found that the topologies of the optimized adaptive landscapes and underlying performance surfaces are largely characterized as a single gradual gradient rather than as rugged, multipeak landscapes with distinct zones. Our results suggest that carnivorans may already occupy a broad adaptive zone as part of a larger mammalian adaptive landscape that masks the form and function relationships of skeletal traits.

Law CJ, Hlusko LJ, & Tseng ZJ. 2025. The carnivoran adaptive landscape reveals trade-offs among functional traits in the skull, appendicular, and axial skeleton. Integrative Organismal Biology. doi.org/10.1093/iob/obaf001

Mammalian skeletal diversity

NSF DBI-2128146