Inferring the palaeobiology of palorchestid marsupials through analysis of mammalian humeral and femoral shape

• Published in: Journal of mammalian evolution Vol. 30; no. 1; pp. 47 - 66
• Main Authors: Richards, Hazel L., Rovinsky, Douglass S., Adams, Justin W., Evans, Alistair R.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.03.2023; Springer Nature B.V
• Subjects: Animal Genetics and Genomics; Anthropology; Biomedical and Life Sciences; Divergence; Endangered & extinct species; Evolutionary Biology; Extinct species; Extinction; Femur; Human Genetics; Humerus; Life Sciences; Limbs; Marsupialia; Marsupials; Morphology; Original Paper; Palorchestidae; Phylogeny; Femur; Geometric morphometrics; Humerus; Functional morphology
• ISSN: 1064-7554; 1573-7055
• DOI: 10.1007/s10914-022-09640-6

The relationship between ecology and morphology of the limbs in living placental mammals is well established and has been used to infer aspects of palaeobiology for many extinct species. However, few studies have applied these principles to extinct marsupials. Palorchestids are a poorly understood extinct family of megafaunal marsupials of particular interest due to their highly robust and unusual limb morphology. Using a comparative sample of humeri and femora from living mammals potentially analogous to palorchestids, we applied three-dimensional geometric morphometric techniques in a phylogenetic comparative framework. We established that humerus and femur shape in living species showed significant associations with size, phylogeny, and substrate use, and found a weak association between humeral shape and diet. We then examined patterns in morphological disparity, modularity, covariance and morphospace occupation in palorchestids relative to comparative living mammals as well as their closest extinct marsupial relatives. We found palorchestid femora to be unremarkable in shape, while their overall and proximal humeral morphology were strongly divergent from all other mammals sampled. Over their evolutionary history, palorchestid distal humeri increasingly resembled those of mammals adapted for tearing and hook-and-pull digging, while other analyses showed various arboreal-like and fossorial-like affinities in humeral shape. Our findings indicate strong asymmetric selection acting on the fore- and hindlimbs in palorchestids, and their unique combination of shape traits suggests they used their forelimbs in a specialised manner that has no direct equivalence either with their extinct relatives or among other mammals alive today.