Paleobiology of Argyrolagus (Marsupialia, Argyrolagidae): an astonishing case of bipedalism among South American mammals

ABELLO, M. A. Y A.M. CANDELA

JOURNAL OF MAMMALIAN EVOLUTION

SPRINGER

Lugar: Berlin; Año: 2019

1064-7554

Argyrolagus constitutes, both for its craniodental and postcranial anatomy, one of themost notably specialized South American Neogene metatherians. Differentiating it fromany other South American mammal, bipedal jumping has been proposed forArgyrolagus, even though this hypothesis was not supported by morphofunctionalstudies. Here, we describe the postcranium of A. scaglai (from the Pliocene ofArgentina), perform a functional analysis, and interpret it against a varied backgroundof locomotor adaptations of extant mammals. The configuration of the joints, thedegree of development and location of the muscular insertions were mainly analyzedand functional indices were evaluated. This study indicates that Argyrolagus hadstabilized glenohumeral and humeroulnar joints, a great development of the armretractor, flexors-extensors of the digits, pronator, and supinator muscles, lowrestrictive humeroradial joint, powerful extensor muscles of the hip, knee, and ankle,good development of the iliac muscle, and restrictive hind limb joints. Jointconfigurations are interpreted to be optimal to resist the impacts during jumping,avoiding dislocation, compatible with digging activity. A compromise between thecapacities to dig and manipulate objects is inferred. It is concluded that Argyrolagushad bipedal jumping locomotion as well as good capacity to dig, constituting anastonishing case of convergence with the small bipedal rodents and small Australianmacropodids. We suggest that bipedal jumping in Miocene and Pliocene argyrolagidsshould not be certainly related to a particular arid environment. Finally, we evaluate theimportance of postcranial features to understand the phylogenetic relationships ofArgyrolagidae in a comprehensive phylogeny of Metatheria.