The influence of island evolution on size-shape relationships in the anatomy of sheep, goats and their relatives

The relationship between anatomical form and body size (allometry) is a fundamental concept in anatomy. Size-shape relationships can be studied across development (ontogenetic allometry), between adults of the same species (static allometry), or between species within a larger clade (evolutionary allometry). In reference to evolutionary allometry, it has been noted that, owing to physical and functional constraints, large and small species vary in body proportions and skeletal anatomy, and are rarely, if ever, isometrically scaled versions of one another. For example, large quadrupedal mammals tend to have relatively shorter distal hind limbs compared to smaller species, to support their increased body mass against gravity.

In general, evolutionary allometric trends can be derived for any given skeletal element within a clade of vertebrates, such that anatomical form can be predicted from body size. However, such allometric trends can break down in the presence of factors that alter selection pressures. For example, life on an island where food resources are limited but the predation risk is reduced has been shown to lead to large changes in body size (insular dwarfism and gigantism) accompanied by changes in morphology not predicted by the allometric trajectory of closely related mainland species (Hennekam et al, 2022). Moreover such morphological changes have been shown to have functional consequences that suggest niche shifts (Hennekam et al, 2023). This project will investigate these issues within the ungulate subfamily Caprinae (sheep, goats and their relatives). They are an ideal group for this project as there around 38 wild species spanning a wide range of body sizes (30-350 kg), the postcranium is generally quite conservative in its morphology (implying that any major changes are likely to be functionally driven), and the clade also contains examples of both island and domestic species. Myotragus is a genus of extinct dwarf goat found on Mallorca and Menorca between 5.3 million and 5,000 years ago. Its closest living relative is the much larger takin, a Himalayan bovid that can reach 400 kg in body mass. Myotragus shows unusual features including forward-facing orbits, ever-growing incisors, and stout metapodials, suggesting it has potentially diverged from the caprine allometric trajectory.

This project has three main objectives:

1. To determine the relationship between size, morphology, ecology, and habitat in the jaws and limbs of a wide sample of extant and extinct caprine genera.
2. To assess the degree to which the allometric relationships are disrupted by life in an island environment. This will be quantified using a case study of the extinct dwarf goat Myotragus.
3. To determine the functional consequences of morphological variation resulting from island dwarfism. This will be explored on a dataset of Myotragus and some of its extant relatives.

These objectives will be addressed using a toolbox of sophisticated techniques such as: 3D surface scanning; microCT scanning; virtual reconstruction; landmark-based shape analysis (geometric morphometrics); and virtual biomechanical simulation (finite element analysis).

This project would suit a candidate with a background in anatomy, zoology, palaeontology or zooarchaeology. Prior experience in geometric morphometrics and/or biomechanics would be a bonus, but is not essential as training will be provided during the course of the PhD. However, it is important that the student is competent in mathematics and data handling. The supervisory team includes expertise in functional morphology, biomechanics and palaeontology.

Interested applicants should contact Dr Phil Cox (philip.cox@ucl.ac.uk) with a CV and a statement of research interests.

To make a formal application, use the following link: https://www.ucl.ac.uk/prospective-students/graduate/research-degrees/cell-and-developmental-biology-mphil-phd . Select a start date of October 2025, and state Dr Philip Cox as the primary supervisor.