The placental mammal order Carnivora is an ideal group for examination of macroevolutionary patterns.  They are exceptionally diverse in ecology and morphology, have an exceptional fossil record, and are well studied in phylogeny, development, and genetics.  We have used Carnivora as a model group for extensive analyses of morphological integration and modularity, functional morphology, macroevolutionary patterns, adaptive radiations, and numerous other topics.  With funding from the Leverhulme Trust, we are studying the evolutionary modularity and biomechanics of the cat vertebral column, incorporating morphometrics, comparative anatomy, and modelling to understand how cats maintain locomotory flexibility at large body sizes.

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Walking the Cat Back: Evolutionary Modularity & Mechanics of the Felid Skeleton

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In this Leverhulme Trust funded project, Team Cat is studying the evolution of cat locomotion by unifying three disparate fields of analysis.  First, we are conducting dissections and biomechanical analyses of cat postcrania, representing the full breadth of cat ecology and size to identify the biomechanical consequences of large body size in cats and the effect of any changes in postcranial muscles and bone shape on cat locomotion.  Second, we are using 3D geometric morphometrics to identify postcranial changes that are associated with increasing size, as well as changes that relate to other factors, such as habitat, prey preference, or killing behaviour.  As previous studies have shown that large cats have relatively more robust limbs for their size, this data will allow us to test if the entire skeleton shows a similar pattern, or if different parts of the skeleton are modified in other ways to allow for the unusual locomotor style observed in cats.  Third, we are analysing the evolutionary relationships among the different parts of the postcranial skeleton with measurement and developmental data.  Functional, genetic, and developmental links between the front of the postcranial skeleton (the forelimbs, pectoral girdle, and anterior vertebral column), and the back of the skeleton exist, but previous studies have shown that these links can be broken in species with unusual reproductive strategies (such as marsupials) or unusual locomotor styles (such as bats).  We will test whether the links across the different elements have been modified from the ancestral placental mammal pattern in order to allow the cats to maintain their crouching posture at large sizes.  We will also be able to combine these data with our biomechanical analyses to test if parts of the skeleton that show similar responses to mechanical stress also show stronger evolutionary correlations than parts that don’t respond similarly.  Our results already demonstrate that cat body size has a complex evolutionary history, and that the postcranial muscles do not scale sufficiently with size, meaning that large cats are relatively weaker than small cats.  Our shape analyses show that the vertebral column of cats is also more complex than thought, with the anterior portion showing strong phylogenetic signal, while the posterior half shows stronger ecological signal. 

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Link to downloadable 3D pdf of dissected tiger forelimb (save and open in pdf viewer)

 

Link to downloadable 3D pdf of dissected lion hind limb  (save and open in pdf viewer)

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