Dr David J Button

The sauropodomorph dinosaurs, the iconic "long-neck" dinosaurs of the Mesozoic, included the largest animals ever to have walked the earth. They have been descibed from every continent, and dominated megaherbivorous niches over much of the world for 135Ma, and also show great diversity, inferred to have been permitted by niche partitioning, itself unusual for such large herbivores. They are hence of great interest not only due to their own je ne sais quoi, but in understanding the driving forces behind gigantism and the physiological, biological and ecological limits acting upon terrestrial life. Their longevity and diversity indicates them as one of the most successful radiations of terrestrial herbivores, and provide a good candidate for detecting evolutionary signals associated with the evolution of herbivory. Additionally, the great size, megaherbivorous role and ubiquitous nature of sauropods must have made them one the most important biotic influences upon the ecosystems in which they dwelled; a thorough understanding for sauropodomorph ecology is imperative for an understanding of Mesozoic ecosystems in general.

Given that the large sauropods must have operated at the limits of biological feasibility, they present many problems and paradoxes, not the least of which was how they secured sufficient food intake. Previous modeling and biomechanical work has focussed largely on the role of the neck in feeding, but the skull, despite its small size, was a highly specialized cropping tool and it own right and a sound, biomechanical, understanding of its function is crucial to understanding feeding.

Previous morphological, macrowear and microwear studies have afforded an overview of sauropod craniodental function and evolution, and have been used to posit hypotheses of ecology (diet, niche partitioning) and macroevolution, with a shift to bulk-feeding at the base of the Sauropoda, followed by certain lineages developing more specialized feeding strategies. However, much remains unclear. Firstly, the trends in certain osteological features, most notably cranial arthrology (the morphology of the sutures and joints in the skull) have are poorly understood, lacking a comprehensive review. Secondly, the biomechanical significance of many of the features invoked in ecological and macroevolutionary hypotheses regarding the sauropodomorph skull have yet to be tested.

My work seeks to tackle both of these problems. One stage of this project concerns inspection of sauropodmorph osteological features, from first-hand observations as far as possible, and in particular a thorough profiling of cranial arthrology (which may have phylogenetic as well as mechanical significance). Phylogenetic optimization will then be utilized to yield a more detailed overview of osteological trends in sauropodomorph cranial evolution. The biomechanical significance, if any, of these characters and those already invoked as functionally significant in the evolution of the sauropodomorph feeding apparatus will be tested utilising Finite Element Analysis.

Finite Element Analysis (FEA) is an engineering technique whereby stress and strain distributions can be calculated in a digital model of a complex shape (such as a skull) under loading (such as by the adductor muculature) by breaking it down into a large (but finite) number of discrete and simple elements, each of which is easily solvable. FEA represents a method which can test biomechanical hypotheses in a quantitative manner. As such it has been widely used to inspect cranial limits and testing hypotheses of funtion in taxa as disparate as theropods and foraminifera, and has been used to great success in multitaxon comparative studies in testing of ecological and behavioural hypotheses.

I am currently involved in producing 3D models of the skulls of the macronarian neosauropod Camarasaurus, which will be compared to an existing model of a sympatric, but very different, taxon- Diplodocus. Each will be subjected to a range of loading conditions, representing different behaviours such as straight, adductor-driven biting and branch stripping. Comparison of skull performance under these regimes will inform hypotheses of differing function and consequent niche partitioning of these taxa based on craniodental anatomy, and provide clarification on the dynamics of a sauropod-dominated ecosystem.

Additionally, the biomechanical significance of cranial characters derived within the sauropodomorpha, such as the marked changes in skull shape and the development of the lateral plates, will be investigated through comparison of these neosauropods to models constructed of the basal taxa Plateosaurus and Massospondylus. Explicit hypothesis testing of features such as the lateral plates and any suture patentcy through comparison of runs of the base Camarasaurus model with one in which the feature in question has been removed (if possible) will then allow definite statements of the biomechanical significance (or lack thereof) of each of these characters, and test their role in evolution and adaptation of the sauropodomorph skull.

This work will see the evolution of the sauropodomorph skull placed in a rigorous biomechanical context for the first time through the application of Finite Element Analysis. This will facilitate testing of the biomechanical tennets of currently invoked hypotheses of the development and application of the sauropodomorph skull towards feeding through time, providing insight into the evolution and ecology of the sauropodomorpha.

Before this, my masters thesis conerned investigating the utility of continuous characters in cladistic analysis and their impact on the phylogeny of pterosaurs.