Postcranial skeleton of the Miocene marsupial Palaeothentes (Paucituberculata, Palaeothentidae): paleobiology and phylogeny

Abstract

This contribution presents a morphofunctional analysis of the previously unknown appendicular skeleton of the paucituberculatans Palaeothentes minutus and Palaeothentes lemoinei from the Santa Cruz Formation (late early Miocene, Santa Cruz province, Argentina), performed in order to infer their locomotor behavior. In addition, a cladistic analysis was conducted to explore the phylogenetic information of postcranial features of Palaeothentes in the context of Marsupialia. The results indicate that Palaeothentes would have been an agile cursorial dweller, with leaping ability, similar to the extant paucituberculatan Caenolestes fuliginosus and the didelphid Metachirus nudicaudatus. This mode of locomotion is evidenced mainly by the following features: proximal location of the deltopectoral crest and bicipital tuberosity, reflecting rapid flexion at the gleno-humeral and elbow joints, respectively; shape of the humero-ulnar and humero-radial joints (deep and high humeral trochlea, deep olecranon fossa, deep trochlear notch, mediolaterally broad proximal trochlear crest), denoting a marked stability for flexion and extension; restrictive acetabulum, showing emphasized congruence at the hip joint; lengthened ischium and prominent femoral tubercle and ischial tuberosity, indicating an increased mechanical advantage of the rectus femoris and hamstring muscles; proximally projected greater trochanter, demonstrating a relatively great mechanical advantage of the gluteal muscles; and configuration of the upper ankle, lower ankle, and transverse tarsal joints, indicative of restrictive rotational movements (right angle between the medial and lateral astragalotibial facets, distal and proximal calcaneo-cuboid facet halves forming a right angle). A cladistic analysis positions Palaeothentes as the sister taxon to the extant Caenolestes, demonstrating that postcranial features support the monophyly of Paucituberculata.