A Three-Dimensional Skeletal Reconstruction of the Stem Amniote Orobates pabsti (Diadectidae): Analyses of Body Mass, Centre of Mass Position, and Joint Mobility

Abstract

Orobates pabsti, a basal diadectid from the lower Permian, is a key fossil for the understanding of early amniote evolution. Quantitative analysis of anatomical information suffers from fragmentation of fossil bones, plastic deformation due to diagenetic processes and fragile preservation within surrounding rock matrix, preventing further biomechanical investigation. Here we describe the steps taken to digitally reconstruct MNG 10181, the holotype specimen of Orobates pabsti, and subsequently use the digital reconstruction to assess body mass, position of the centre of mass in individual segments as well as the whole animal, and study joint mobility in the shoulder and hip joints. The shape of most fossil bone fragments could be recovered from micro-focus computed tomography scans. This also revealed structures that were hitherto hidden within the rock matrix. However, parts of the axial skeleton had to be modelled using relevant isolated bones from the same locality as templates. Based on the digital fossil, mass of MNG 10181 was estimated using a model of body shape that was varied within a plausible range to account for uncertainties of the dimension. In the mean estimate model the specimen had an estimated mass of circa 4 kg. Varying of the mass distribution amongst body segments further revealed that Orobates carried most of its weight on the hind limbs. Mostly unrestricted joint morphology further suggested that MNG 10181 was able to effectively generate propulsion with the pelvic limbs. The digital reconstruction is made available for future biomechanical studies.

Three‐dimensional mobility and muscle attachments in the pectoral limb of the Triassic cynodontMassetognathus pascuali(Romer, 1967)

“…; Nyakatura et al. ). To circumvent this, we established an articular cartilage thickness of 0.25 mm based on relationships for mammalian articular cartilage (Simon, ).…”

“…; Nyakatura et al. ). Further, we reconstruct the origins and insertions of the shoulder musculature using an updated, extended extant phylogenetic bracket, and map them onto the 3D pectoral limb skeleton of Massetognathus pascuali .…”

“…Using digital models of fossil material derived from micro-computed tomography (lCT), we interactively assess articular function at the shoulder and elbow joints (e.g. Pierce et al 2012;Nyakatura et al 2015). Further, we reconstruct the origins and insertions of the shoulder musculature using an updated, extended extant phylogenetic bracket, and map them onto the 3D pectoral limb skeleton of Massetognathus pascuali.…”

3‐D range of motion envelopes reveal interacting degrees of freedom in avian hind limb joints

“…Paleontologists often seek to make inferences about function in extinct taxa known only from skeletal remains (e.g. Galton, 1971;Bramwell & Whitfield, 1974;Stevens & Parrish, 1999;Gishlick, 2001;Senter & Robins, 2005;Senter 2006;Carpenter & Wilson, 2008;Senter, 2009;Mallison, 2010a,b;Pierce et al 2012;Hutson & Hutson, 2014, 2015Nyakatura et al 2015;White et al 2015White et al , 2016. An accurate assessment of ROM about each of a joint's DoFs can test hypotheses of behavior by eliminating those that require poses or movements outside the range of accessibility (Senter, 2005(Senter, , 2009Brougham & Brusatte, 2010;Pierce et al 2012).…”

A quantitative evaluation of physical and digital approaches to centre of mass estimation

“…Recent advances in computing technology have seen digital modelling used more and more frequently as a method for calculating CoM position (e.g. Henderson, 1999;Hutchinson et al 2007;Ren & Hutchinson, 2008;Amit et al 2009;Bates et al 2009aBates et al , 2016Allen et al 2013;Maidment et al 2014;Park et al 2014;Paxton et al 2014;Nyakatura et al 2015;Peyer et al 2015). Digital models offer some advantages over physical methods including ease of data sharing and simple manipulation for sensitivity analyses and repeatability analyses, in addition to the advantages of scanning procedures such as computed tomography (CT).…”