Muscular reconstruction and functional anatomy of Plesiotypotherium achirense (Mammalia, Notoungulata, Mesotheriidae) from the late Miocene of Bolivia

PUJOS, F.; FERNÁNDEZ-MONESCILLO, M.; ANTOINE, P.-O.; BERNARDINO, MAMANI QUISPE

General Roca

Congreso; 11Th Congreso de la APA; 2017

We provide a muscular reconstruction and we infer functional properties of the forelimb of Plesiotypotherium achirense Villarroel, 1974 from the late Miocene of Achiri, Pacajes Province, Bolivia. The osteological sample available for the forelimb of this species (study based in seventy-eight postcranial elements) is much wider than for any other mesotheriid notoungulate, thus providing exceptional insights about osteological features and muscular areas. Recent mesotheriid-focused studies have concluded to a highly conservative postcranial skeleton, with a scratch-digging faculty. In order to test this hypothesis, our comparison sample included extant mammals with similar functional abilities, such as Vombatus ursinus, Tamandua sp., Hystrix cristata, Taxidea taxus, Orycteropus afer, and Nasua nasua. As a result, Plesiotypotherium achirense shows typical fossorial osteological structures: i) distally located suprascapular fossa, ii) well-developed deltoid crest, iii) complete scapular girdle, iv) well-developed entepicondyle, ectepicondyle, and supracondylar crest of the humerus, v) enlarged olecranon, and vi) strong manus with robust carpals and metacarpals and phalanges. The form-function forelimb complex was then inferred thanks to osteological features and muscular reconstruction: the different muscular groups acted together combining their function and resulting in a biomechanical average, perfectly compatible with a scratch-digging life style, with favored limb and humeral retraction, and antebrachium supination pronation and flexion.