Adaptations for digging in the forelimb muscle anatomy of the southern brown bandicoot (Isoodon obesulus) and bilby (Macrotis lagotis)

Abstract

Bandicoots and bilbies (Peramelemorphia) represent a distinct lineage within the marsupial adaptive radiation, which despite several curious anatomical traits has received little morphological attention. Many bandicoot species (family Peramelidae) dig for subterranean food, while bilbies (family Thylacomyidae) employ their forelimbs to dig extensive burrow systems for shelter. In the current study, dissections of the southern brown bandicoot (Isoodon obesulus) (n = 7) and greater bilby (Macrotis lagotis) (n = 4) provide the first anatomical descriptions of forelimb musculature in these species. The anatomical arrangement of forelimb muscles in I. obesulus and M. lagotis differs from that of other marsupials and corresponds to the aclaviculate pectoral girdle and modified arrangement of digits in the study species. Comparative and functional interpretations indicate that the forelimb of I. obesulus is well equipped for scratch digging and demonstrates muscular modifications in order to generate large out-forces. The bones of the forelimb, and in particular the antebrachium, are relatively short, stout bones, improving both their resistance to mechanical forces and providing a mechanical advantage via a reduced out-lever length. There has been an increase in the absolute volume of muscles employed during digging, thereby increasing the magnitude of the in-force. Increased in-lever lengths have been achieved via the migration of muscle insertions, including the elongate olecranon for the insertion of the m. triceps brachii, and the distal migration of the humeral attachments of the teres major, latissimus dorsi and superficial pectoral muscles.

Functional Morphology of the Forelimb of the Nine-Banded Armadillo (Dasypus novemcinctus): Comparative Perspectives on the Myology of Dasypodidae

“…Similar to other terrestrial scratch-diggers studied (e.g., Gambaryan 1974;Moore et al 2013;Warburton et al 2013;Rupert et al 2015), forelimb muscle mass in D. novemcinctus is concentrated in the limb retractor, elbow extensor, and digital flexor muscle groups. These functional groups combined accounted for over 80 % of total forelimb muscle mass.…”

Going underground: postcranial morphology of the early Miocene marsupial mole Naraboryctes philcreaseri and the evolution of fossoriality in notoryctemorphians

“…philcreaseri, we compared its Index of Fossorial Ability (IFA; sometimes referred to as Olecranon Length Index) -a commonly used metric that is strongly correlated with the degree of fossoriality in various groups of mammals (Vassallo, 1998;Vizcaino et al, 1999;Elissamburu and Vizcaíno, 2004;Lagaria and Youlatos, 2006;Warburton et al, 2013;Woodman and Gaffney, 2014) -with that of Notoryctes and other fossorial and subterranean mammals (table 1). We calculated IFA as (olecranon length/(total ulnar length-olecranon length))*100, following Vizcaino and Milne (2002).…”

“…2a, c), and the proportionately robust and elongate olecranon of the ulna ( fig. 4a), are also all characteristic of a fossorial or subterranean lifestyle (Reed, 1951;Lehmann, 1963;Taylor, 1978;Thorington et al, 1997;Warburton, 2006;Warburton et al, 2013). Collectively, they reflect enlargement of the m. triceps longus, mm.…”

“…reflecting enlargement of the scapular (long) head of the m. triceps brachii. Enlargement of the triceps is common in fossorial mammals, particularly scratch diggers, and is also associated with elongation of the olecranon on the ulna (resulting in a larger IFA; Windle and Parsons, 1899;Taylor, 1978;Gasc et al, 1986;Stein, 1986;Lagaria and Youlatos, 2006;Warburton, 2006;Warburton et al, 2013). In Na.…”

Hind limb myology of the southern brown bandicoot (Isoodon obesulus) and greater bilby (Macrotis lagotis) (Marsupialia : Peramelemorphia)

“…Following the recent description of the forelimb muscular anatomy (Warburton, Gregoire et al 2013), the current study provides detailed myological descriptions of the hind limb of the southern brown bandicoot (Isoodon obesulus) and greater bilby (M. lagotis). The descriptions, muscle maps and comparative notes reported here provide baseline morphological data for an examination of the musculoskeletal basis of bandicoot locomotion, and for palaeontologists and neontologists investigating morphological evolution in living and fossil bandicoots.…”