Testing the occurrence of convergence in the craniomandibular shape evolution of living carnivorans*

Abstract

Convergence consists in the independent evolution of similar traits in distantly related species. The mammalian craniomandibular complex constitutes an ideal biological structure to investigate ecomorphological dynamics and the carnivorans, due to their phenotypic variability and ecological flexibility, offer an interesting case study to explore the occurrence of convergent evolution.Here, we applied multiple pattern-based metrics to test the occurrence of convergence in the craniomandibular shape of extant carnivorans. To this aim, we tested for convergence in many dietary groups and analyzed several cases of carnivoran convergence concerning either ecologically equivalent species or ecologically similar species of different body sizes described in the literature.Our results validate the occurrence of convergence in ecologically equivalent species in a few cases (as well as in the case of giant and red pandas), but almost never support the occurrence of convergent evolution in dietary categories of living carnivorans. Therefore, convergent evolution in this clade appears to be a rare phenomenon. This is probably the consequence of a complex interplay of one-to-many, many-to-one, and many-to-many relationships taking place between ecology, biomechanics, and morphology.

Mandible shape variation and feeding biomechanics in minks

“…Additionally, mandible morphology has been shown to be evolutionarily more plastic, reflecting dietary adaptations more accurately than the cranium, whose morphological evolution must respond to conflicting functional demands 23 – 25 . However, in the last decades, the consolidation of geometric morphometric methods has resulted in an increase in this type of study, which have revealed that mandible shape (i.e., all its geometric features except for size, position, and orientation) in carnivorans is not only related to function (i.e., mastication), but to a complex interaction of factors such as evolutionary history, body size, sexual dimorphism, diet and, in carnivorous species, prey size 16 , 23 , 26 – 31 .…”

Digest: Taxonomically inclusive and quantitative tests for convergence*

“…θ ranges from 0°to 180°, with lower values indicating convergence. Tamagnini et al (2021) calculated these based on a shared state (diet) expected to cause convergence. This involves calculating θ and phylogenetic distance (p) for each pair of taxa with that state.…”

“…All three of these methods rely on novel estimates of ancestral states and were conceived within the last decade. Tamagnini et al (2021) contribute to a growing trend of applying phylogenetic comparative analyses to investigate historically qualitatively described phenomena. Tamagnini et al's (2021) findings that convergence is uncommon on the ordinal level but not too rare on the species level indicate the importance of taxonomic scale and demonstrate that interactions between biomechanics, ecology, and morphology are more nuanced than dietary categorizations.…”

“…Unfortunately, most documented cases of convergence are qualitative, limiting our understanding of its prevalence and making it difficult to identify trends among and across taxonomic groups. In this issue, Tamagnini et al (2021) present the most taxonomically inclusive quantitative evaluation of convergence in Carnivora to date by employing novel analyses from the field of phylogenetic comparative methods.…”

“…The last method Tamagnini et al (2021) employ is the Wheatsheaf index, which calculates degree of convergence (Arbuckle et al 2014). Like θ, this penalizes phylogenetic closeness by dividing the phenotypic distance between taxa (d ij ) by their scaled phylogenetic distance (p ij ; Fig.…”