Evolution and ecomorphology of the avian foot: the morphology of the tarsometatarsus in birds and its responses to evolutionary changes in foot use

Thesis

Accipitriformes, Strigiformes, and Falconiformes are the three extant raptorial avian clades, most members of which use their feet to kill and carry prey. The disparate grouping of these clades with similar foot use has been hypothesised to result from retention of raptoriality from a telluravian ancestor, which has not been tested using ecomorphological methods. I evaluated the hypothesis by testing the anatomical correlates of raptoriality and other foot uses in extant birds using geometric morphometrics and phylogenetic comparative shape analysis on first the entire tarsometatarsus bone, and then on the proximal articular surface and hypotarsus (a plantar channel through which flexor tendons run). I then mapped the ancestral states of raptoriality across the phylogeny, including fossil taxa, as well as the ancestral states of 14 other foot uses. Centroid size, body mass, flightlessness, zygodactyl digit orientation, force grip foot use, and raptoriality all had significant and independent effects on whole tarsometatarsus shape, and explain approximately 26% of tarsometatarsus shape variation. Hypotarsus shape is a statistically significant indicator of raptoriality in birds: raptorial birds tend to possess a deep and wide monosulcate hypotarsus. This relationship can be used to infer raptorial foot use in stem taxa throughout Telluraves known only from fossils. Using these inferred states in ancestral character estimation demonstrates that all extant raptorial groups have convergently evolved raptoriality, contradicting existing hypotheses of a raptorial ancestry of Telluraves as a whole. However, this does not rule out the occurrence of carnivory in the ancestor of Telluraves. Cursoriality, ability to hold down objects, digital manipulation, scansoriality, and hanging and clinging behaviour were determined to be convergent within Telluraves. Force grip foot use, walking ability, perching ability, and anisodactyl digit orientation were determined to be ancestral to Telluraves.

Authors: Tronrud, B

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: raptoriality in telluraves; avian evolution; phylogenetic geometric morphometric analyses
• Subjects: Birds; Vertebrates, Fossil; Paleobiology