Meeting Abstract

26.2  Saturday, Jan. 4 13:45  Proximal caudal vertebral morphology in relation to tail length among primates and other mammals RUSSO, G.A.; The University of Texas at Austin; Northeast Ohio Medical University grusso@neomed.edu

Tail reduction/loss independently evolved in a number of mammalian lineages. One prerequisite to appropriately contextualizing and understanding its significance is the ability to confidently establish tail length from fossil material. This study examines how caudal vertebral anatomy varies among primates and other mammals (carnivores, diprotodonts, pilosans, rodents, and tree shrews; N=333) known to differ in relative tail length (RTL; =tail length/[head+body length] x 100). Linear and angular measurements with known biomechanical significance were collected on first, mid-proximal, and transition caudal vertebrae, and their relationship with RTL was assessed using phylogenetic generalized least-squares regression methods. Compared to shorter-tailed taxa, longer-tailed taxa possess a greater number of caudal vertebral features associated with enhanced proximal tail mobility (e.g., more circularly-shaped cranial articular surfaces), as well as greater surface area for attachment and improved leverage of basal tail musculature (e.g., more laterally expanded and caudally oriented transverse processes). Multivariate models constructed from the extant primate data were used to predict the RTLs of two extinct subfossil lemurs with associated caudal vertebrae. The predicted RTL of Palaeopropithecus was 36 (i.e., tail is shorter than ½ head and body length) and that of Archaeolemur was between 109 and 143 (i.e., tail longer than total head and body length). These results have implications for our ability to track evolutionary changes in tail length and also provide an anatomical basis for future studies of tail kinematics. Supported by NSF DDIG BCS-1156016 and The Leakey Foundation.