Three dimensional digital reconstruction of the jaw adductor musculature of the extinct marsupial giant Diprotodon optatum.

Alana C Sharp

doi:10.7717/peerj.514

Abstract

The morphology and arrangement of the jaw adductor muscles in vertebrates reflects masticatory style and feeding processes, diet and ecology. However, gross muscle anatomy is rarely preserved in fossils and is, therefore, heavily dependent on reconstructions. An undeformed skull of the extinct marsupial, Diprotodon optatum, recovered from Pleistocene sediments at Bacchus Marsh in Victoria, represents the most complete and best preserved specimen of the species offering a unique opportunity to investigate functional anatomy. Computed tomography (CT) scans and digital reconstructions make it possible to visualise internal cranial anatomy and predict location and morphology of soft tissues, including muscles. This study resulted in a 3D digital reconstruction of the jaw adductor musculature of Diprotodon, revealing that the arrangement of muscles is similar to that of kangaroos and that the muscle actions were predominantly vertical. 3D digital muscle reconstructions provide considerable advantages over 2D reconstructions for the visualisation of the spatial arrangement of the individual muscles and the measurement of muscle properties (length, force vectors and volume). Such digital models can further be used to estimate muscle loads and attachment sites for biomechanical analyses.

Highlights

Understanding the relationship between form and function is the aim of biomechanical analysis of extinct or extant vertebrates (Lauder, 1995)
Soft tissues can be preserved in the fossilised remains, but in the majority of cases it is necessary to infer the arrangement of muscles and ligaments from skeletal remains in order to predict muscle function, skeletal movement, and possible behaviour (Lauder, 1995; Witmer, 1995)
Dentition The Diprotodontidae, which includes a diverse group of vombatomorphian marsupials, are characterised by relatively simple bilophodont molars, oval to triangular P3 in dorsal aspect, and six upper and two lower incisors

Summary

Introduction

Understanding the relationship between form and function is the aim of biomechanical analysis of extinct or extant vertebrates (Lauder, 1995). Soft tissues can be preserved in the fossilised remains, but in the majority of cases it is necessary to infer the arrangement of muscles and ligaments from skeletal remains in order to predict muscle function, skeletal movement, and possible behaviour (Lauder, 1995; Witmer, 1995). Where there are no close living analogues, palaeontologists must rely on fossil material alone to reconstruct soft tissues. This in turn requires a broad knowledge of vertebrate anatomy. Bone and soft tissue structures were described and illustrated using line drawings in standard anatomical planes and often only one or two diagrams were given

Methods

Results

Conclusion