Antiquity of forelimb ecomorphological diversity in the mammalian stem lineage (Synapsida)

Abstract

Mammals and their closest fossil relatives are unique among tetrapods in expressing a high degree of pectoral girdle and forelimb functional diversity associated with fully pelagic, cursorial, subterranean, volant, and other lifestyles. However, the earliest members of the mammalian stem lineage, the “pelycosaur”-grade synapsids, present a far more limited range of morphologies and inferred functions. The more crownward nonmammaliaform therapsids display novel forelimb morphologies that have been linked to expanded functional diversity, suggesting that the roots of this quintessentially mammalian phenotype can be traced to the pelycosaur–therapsid transition in the Permian period. We quantified morphological disparity of the humerus in pelycosaur-grade synapsids and therapsids using geometric morphometrics. We found that disparity begins to increase concurrently with the emergence of Therapsida, and that it continues to rise until the Permo-Triassic mass extinction. Further, therapsid exploration of new regions of morphospace is correlated with the evolution of novel ecomorphologies, some of which are characterized by changes to overall limb morphology. This evolutionary pattern confirms that nonmammaliaform therapsid forelimbs underwent ecomorphological diversification throughout the Permian, with functional elaboration initially being more strongly expressed in the proximal end of the humerus than the distal end. The role of the forelimbs in the functional diversification of therapsids foreshadows the deployment of forelimb morphofunctional diversity in the evolutionary radiation of mammals.

Phylogeny and foraging behaviour shape modular morphological variation in bat humeri

“…Statistically significant phylogenetic signal in our datasets follows similar patterns previously reported for cranial morphology in bats (Arbour et al, 2019;Hedrick et al, 2019). The magnitude of phylogenetic signal in postcranial morphological diversity in mammals remains unclear, with studies reporting a significant effect in carnivorans and marsupials (Janis et al, 2020;Martin-Serra et al, 2017;Martín-Serra et al, 2014), but non-significant at macroevolutionary scales (Lungmus & Angielczyk, 2019). Further studies are needed to understand the macroevolutionary patterns of morphological disparity in the mammalian postcranium and the role of ecology and phylogeny influencing those patterns.…”

“…Forelimb ecomorphological diversity has been associated with the ecological and taxonomic diversification of mammals, showing an evolutionary trajectory of increasing forelimb disparity (Lungmus & Angielczyk, 2019). Our PLM results revealed a significant effect of evolutionary history and ecology on humeral shape at the three levels studied (i.e.…”

Effects of taphonomic deformation on geometric morphometric analysis of fossils: a study using the dicynodontDiictodon feliceps(Therapsida, Anomodontia)

“…Although initially developed in the study of extant organisms, geometric morphometrics has also been used extensively to study fossil taxa, including representatives of all major vertebrate groups (Botha & Angielczyk, 2007;Deeming & Mayr, 2018;Pérez-Ben, Báez & Schoch, 2019;Price et al, 2019;Felice et al, 2019). These techniques have been used for biomechanical modeling (Pierce, Angielczyk & Rayfield, 2008;Polly et al, 2016) and to quantify the evolution of morphological disparity (Brusatte et al, 2012;Lungmus & Angielczyk, 2019), evolutionary rates (Adams, 2014), and ecological adaptions (Grossnickle & Newham, 2016). However, in contrast to extant systems, where the effects of biased sampling can be easily controlled, geometric morphometric studies on fossils include an additional, abiotic source of morphological variation: that of taphonomic deformation.…”

Manual dexterity of mice during food-handling involves the thumb and a set of fast basic movements

“…Functional diversity of the forelimb is a hallmark of mammalian evolution [1]. Mammalian hands evolved around a basic skeletal structure, and the first digit (D1, pollex) often features prominently in these specializations [2].…”