Multidisciplinary approaches to the evolutionary history of felids: phylogeny disparity and biomechanics in living and fossil cats

As a key innovation in the evolution of jawed vertebrates, biting permits a diverse array of feeding strategies and, as a consequence, also successful expansion into niches. Various anatomical adaptations underpin different feeding functions. Our understanding of the relationship between form and function is thus key to teasing out evolutionary changes related to skull and jaw biomechanics function. However, quantitative analyses of function and their associations to structural modifications and anatomical constraints require novel approaches and redefinition of current paradigms. To study function, we will use several metrics, in particular bite force. This offers a good quantitative proxy, as it is represented by a single numerical value that summarises multiple functional parameters, including craniofacial and jaw configuration, muscle position, and muscle size. However, bite force is strongly correlated with body size (the bigger the animal the more powerful its bite). For this reason, a standardised and size-independent relative bite force will be used to compare the variation in bite force that is exclusively linked to function. As a case-study, we will use cats (Family Felidae) to analyze feeding function, and its relation to skull shape, body size, and evolutionary history. Cats are an excellent study group for biomechanical analyses. Contrary to popular belief, their seemingly conservative skull morphology is in fact capable of a wide range of feeding-related functions, particularly among smaller cats. Cats share a relatively recent ancestry (around 10 million years for the extant cats' radiation and 20-25 million years for the most basal stem members of the family), are extremely diverse (41 living species), exhibit a spectrum of body sizes (5 to 300+ kg), and are widely distributed. All these elements suggest that the group underwent a rapid radiation, culminating in some of the top predators of past and present ecosystems (e.g. lions and sabre-tooth cats). The project consists of two major and integrated parts. First, we will test for patterns of evolution in functional traits. This will be accomplished by using a suite of numerical analytical protocols (loosely assembled under the umbrella of phylogenetic comparative methods). These methods allow us to incorporate phylogenetic information into the dataset of functional traits and test for phylogenetic signals or any patterns in trait changes along the branches of the phylogenetic tree. Testing for the effects of phylogeny in functional data is important because some of the variability we observe in the data may actually be because of the relatedness of the species under comparison. For instance, smaller cats show a great deal of variation in standardised bite force data but the larger cats (great cats) show far less variance. There may truly be some biological reason behind this; perhaps smaller cats occupy diverse functional niches. However, the smaller cats are taxonomically diverse and belong to multiple lineages, whereas the great cats are all closely related; the greater variability of functional values in smaller cats and the lower variance in larger cats could very well be attributed to phylogenetic distances. Thus, the effects of phylogeny on the data must be tested in order to understand the evolutionary constraints or processes of functional traits. Second, we will compare changes in functional traits in relation to changes in morphology. This will be accomplished by using geometric morphometrics. This method uses landmarks to capture salient features of interest in the skulls and jaws of cats and allows for identifications of patterns in shape change with increasing body size or with phylogeny (within or across taxonomic groups). Patterns of shape change in skulls can be compared with changes in functional traits to identify key morphological features that may be associated closely with function.

As one of the most successful, highly specialized, and ubiquitous groups of top mammalian predators in many of today's terrestrial ecosystems, cats (Felidae) offer a benchmark for integrated macroevolutionary, macroecological, and morphofunctional investigations. This proposal sets out to explore changes in the biomechanical performances of the cranial musculoskeletal system across the spectrum of past and present felid diversity, in particular their jaw mechanics, and to re-evaluate critically functional paradigms related to feeding. To this end, we propose to undertake a comprehensive phylogenetic analysis of osteological characters (cranial and postcranial) of all extant and most extinct felids. The interrelationships of felids are in a considerable state of flux, and several domains of cat phylogeny, especially among the smallest species, remain unresolved. The phylogenetic component of this proposal is especially important for the smaller cats. Despite their less conspicuous appearance relative to their more fierce and more popular relatives, small cats are very diverse and reveal a surprising amount of variance in biting forces. The detailed phylogeny will inform patterns of change in biomechanical features of interest, and will allow us both to assess the tempo and mode of functional modifications and to disentangle evolutionary and ecological components of craniofacial remodelling in the history of the group. Application of advanced techniques in the field of phylogenetic comparative methods is of paramount importance for resolving the impact of phylogenetic, ecological, and morphological factors on feeding biomechanics as well as for assessing the biomechanical performance of superficially similar fossil (e.g. sabre-toothed cats) and extant taxa (e.g. small cats). Key issues include tempo and mode of functional changes; quantification of cranial functional allometry; analysis of rates of evolution and morphological diversification; life-trait histories.

Among the activities included in the 'public understanding of science' domain is our strong commitment to high-quality school teaching. A solid grasp of basic principles of evolution and an adequate knowledge of the past pave the way to a better understanding and appreciation of the living world, and offer a useful tool for making predictions for the future. The educational component of this proposal is high. Both school children and their teachers will benefit from acquiring a basic knowledge of some of the most exciting and cutting-edge developments in current evolutionary research. The contributions of evolutionary theory provide strong pillars for contemporary science teaching in the UK, and play an almost unrivalled and fundamental role in students' learning progression, from basic tenets of a discipline through to the development of more integrated, synthetic and analytical thinking. The proposed research may also assist teachers in developing courses in general biology, earth sciences and natural history. School teaching will involve a series of informal lectures aided by audio-visual presentations (e.g. PowerPoint; slide projection) and demonstrations with full displays of fossil specimens, rock samples, charts, and other methods. We are committed to dissemination of results in the form of basic lectures in palaeontology, general biology, and geology at schools or public libraries, or in the form of slightly more formal presentations on specific topics at various natural history associations, or in the form of semi-technical papers at learned societies, including museums and centres of higher education. The project provides countless opportunities for Master and PhD students and for postdoctoral scientists who wish to engage in different fields of palaeobiological research, from theoretical and practical aspects of phylogeny reconstruction to macroevolutionary analyses. I would be interested in guiding and supervising students who want to explore deep time macroevolutionary patterns in different groups of organisms across different crucial periods. Results from this research will also be presented to undergraduate students as case studies in palaeontology. At a more general level, students will familiarize with some of the most hotly debated, current topics in vertebrate paleontology, and will benefit from the exploration of multiple facets of comparative methods in evolutionary biology. The results will inform teaching courses and be used to strengthen and widen public engagement. At undergraduate level, we will ensure that the results from this research enrich classes in palaeontology and evolutionary biology, especially by providing insights into collection-based research, assembly and management of fossil data, and development of analytical skills. At graduate level, this reasearch can be developed along several parallel lines of investigation through student recruitment, admission and training, all of which will take place under the umbrella of the University of Bristol. Enthusisatic students with an interest in evolutionary palaeobiology will be offered opportunities to embark on PhD projects that explore similar or related topics. At postdoctoral level, there will be scope to bid for additional grants that will extend the scope of the proposed research, and that will employ researchers with an interest in comparing and contrasting patterns from the fossil record throughout Earth's history, at a local or global geographic scale. We have made preliminary contacts with several societies and libraries within the Bristol City Council area, and has received positive and enthusiatic responses thus far from two libraries, the Bristol City Museum, the Geologist Section of the Bristol Naturalists' Society, and the Bristol Museums, Galleries & Archives Service. A broad circulation of results on a national and international scale will be ensured through interaction with the Press Office at University of Bristol.