Conical and sabertoothed cats as an exception to craniofacial evolutionary allometry

Abstract

Among evolutionary trends shaping phenotypic diversity over macroevolutionary scales, CREA (CRaniofacial Evolutionary Allometry) describes a tendency, among closely related species, for the smaller-sized of the group to have proportionally shorter rostra and larger braincases. Here, we used a phylogenetically broad cranial dataset, 3D geometric morphometrics, and phylogenetic comparative methods to assess the validity and strength of CREA in extinct and living felids. To test for the influence of biomechanical constraints, we quantified the impact of relative canine height on cranial shape evolution. Our results provided support to CREA at the family level. Yet, whereas felines support the rule, big cats, like Pantherinae and Machairodontinae, conform weakly if not at all with CREA predictions. Our findings suggest that Machairodontinae constitute one of the first well-supported exceptions to this biological rule currently known, probably in response to the biomechanical demands and developmental changes linked with their peculiar rostral adaptations. Our results suggest that the acquisition of extreme features concerning biomechanics, evo-devo constraints, and/or ecology is likely to be associated with peculiar patterns of morphological evolution, determining potential exceptions to common biological rules, for instance, by inducing variations in common patterns of evolutionary integration due to heterochronic changes under ratchet-like evolution.

Beyond CREA: Evolutionary patterns of non‐allometric shape variation and divergence in a highly allometric clade of murine rodents

“…Many studies of mammalian cranial shape evolution are consistent with the concept of CREA as a result of biomechanics (e.g. Cardini et al, 2015;Figueirido et al, 2013Figueirido et al, , 2014Tamagnini et al, 2017Tamagnini et al, , 2023, and the effect was recently demonstrated in a genus of marsupial rock-wallabies (Mitchell, Potter, et al, 2024).…”

“…Many studies of mammalian cranial shape evolution are consistent with the concept of CREA as a result of biomechanics (e.g. Cardini et al., 2015 ; Figueirido et al., 2013 , 2014 ; Tamagnini et al., 2017 , 2023 ), and the effect was recently demonstrated in a genus of marsupial rock‐wallabies (Mitchell, Potter, et al., 2024 ). However, the view in Mitchell, Sherratt, and Weisbecker ( 2024 ) suggests that CREA reflects one part of biomechanical evolution as far as it pertains to allometry, but that changes in dietary regime will result in shape changes not captured by CREA.…”

“…This results in a much wider gape, consistent with the benefits of larger gapes in carnivorous rodents (Hennekam et al., 2020 ; Satoh & Iwaku, 2006 ; Williams et al., 2009 ) and specifically the rakali (Fabre et al., 2017 ). The departure from the common allometric line thus reflects the carnivorous species' functional shift from omnivory to carnivory, which is thought to occur at the expense of bite force at the molars (Fabre et al., 2017 ); a similar departure from CREA due to a larger gape has also been observed in sabre‐toothed cats (Tamagnini et al., 2023 ). By contrast, the specialised grass‐feeding broad‐toothed rat Mastacomys and granivore rabbit‐rat Conilurus penicillatus score low on both the residual PC1 and 2, reflecting curved anterior rostra and relatively smaller cranial vaults.…”

“…However, the view in Mitchell, Sherratt, and Weisbecker (2024) suggests that CREA reflects one part of biomechanical evolution as far as it pertains to allometry, but that changes in dietary regime will result in shape changes not captured by CREA. This is indeed the case for a range of mammals covered in Mitchell, Sherratt, and Weisbecker (2024) and particularly well documented in felids (Tamagnini et al, 2017(Tamagnini et al, , 2023. The biomechanical insights that can be gained from the CREA pattern are therefore not complete if nonallometric processes of selection also contribute to cranial shape variation.…”

Facing the facts: adaptive trade‐offs along body size ranges determine mammalian craniofacial scaling

“…However, CREA does not appear to be universal. Several studies have since noted a range of cases that seemingly contradict the predictions of CREA (Hautier et al, 2014;De Muizon et al, 2015;Flores, Giannini & Abdala, 2018;Law et al, 2018;Mitchell et al, 2018;Tamagnini et al, 2023). Furthermore, there are many examples of small mammals with relatively elongate faces, from marsupial honey possums (Tarsipes rostratus) and long-nosed potoroos (Potorous tridactylus) to placental elephant shrews (Macroscelidea) and nectar-feeding phyllostomid bats (Rosenberg & Richardson, 1995;Panchetti et al, 2008;Mitchell et al, 2018;Rossoni et al, 2019), which appear to rule out a short face as a requisite trait of small body size.…”