Convergent carnivores or divergent dasyurids? Inferring predation and locomotor strategies of extant and extinct carnivorous marsupials from locomotor shape.

Abstract

Predation pressure shapes ecosystems via selection on locomotor form and function. To explore this link, we grouped 48 species of predatory mammals into five hunting-strategy clusters: Anteaters, Opportunistic Grapplers, Large Grapplers, Opportunistic Pouncers, and Social Hunters, and asked whether their locomotor shape (limb posture through the stride) reliably distinguished these clusters. We digitised 115 side-view stride sequences across these species, performed Procrustes alignment and principal component analysis on per-stride shapes, and analysed symmetrical (walking) and asymmetrical (galloping/bounding) gaits. In symmetrical gaits, phylogeny accounted for the largest share of locomotor variation, but hunting strategy still explained a significant portion, whereas gait type made only a weak contribution and body mass was not significant. These slower, more economical gaits showed relatively broad overlap among hunting groups, although Social Hunters tended to use more upright limb postures and Grappling species more crouched and extended forelimb configurations. In asymmetrical gaits, differences among hunting strategies were stronger, while gait type and body mass again contributed little. Social Hunters showed larger limb and spinal excursions, whereas Opportunistic Pouncers occupied a more restricted region of locomotor space. The stronger separation among hunting groups during asymmetrical gaits suggests that ecological specialization is expressed most clearly in high-performance behaviours such as acceleration, manoeuvring, and prey capture, rather than in economical walking. We then placed the extinct marsupial predator, the thylacine (Thylacinus cynocephalus), within this framework using archival footage of walking. Its symmetrical-gait centroid was predominantly associated to Opportunistic Pouncer across classifiers. These results show that locomotor biomechanics are associated with hunting ecology, but that these ecological patterns are embedded within substantial phylogenetic structure; they also suggest that this relationship may help inform ecological inference in extinct species.