William J. E.Crabbe *1, Thomas H. P. Harvey 1, Duncan J. E. Murdock 2 & Mark A. Purnell 1
1 School of Geography, Geology and the Environment, University of Leicester, Leicester, LE1 7RH, UK; wc117@leicester.ac.uk
2 Oxford University Museum of Natural History, University of Oxford, Oxford, OX1 3PW, UK
Skeletons are one of the most vital developments in animal evolution, having been developed by every major animal group (Murdock 2020).In particular they have acted as the scaffolding for evolution and diversification of the vertebrate lineage over the last 500 million years,ultimately culminating in the evolution of humans.While we may imagine a skeleton as the hard, internal framework of an animal such as that possessed by humans, a skeleton can be defined as any mineralized structure produced by an organism.The earliest vertebrate tissues are represented by the conodonts–an extinct group of jawless, eel-like animals that first occurred in the Cambrian Period around 500 million years ago. They lack an internal skeleton; instead their skeletons are represented by tooth-like elements that form complex apparatuses within their mouths and throats that were used for food gathering (see Fig. 1B).Our research revolves around the earliest group of these animals, known as the ‘paraconodonts’. These animals are known solely from their microscopic phosphatic elements, which range in form from simple cones, to distinct U- and W- shaped elements known as Westergaardodina (Fig. 1C). The growth of the coniform elements is well constrained while the growth and development of Westergaardodina remains problematic. Through high-resolution 3D imaging and examination of internal structure of exceptionally preserved fossils (Fig. 1C)we aim to resolve the growth of these problematic elements and their relationships. The results of this research will greatly enhance our understanding of the origins of the skeleton in vertebrates.
Fig 1. A: Reconstruction of the conodont (from Discover magazine 1996). B: Model of an example skeletal apparatus present within the mouth and throat of the conodont (from Purnell and Donoghue 1997). C: Tooth-like elements of the problematic paraconodont Westergaardodina displaying exceptional preservation of internal growth structure.
References
Murdock, D.J.E. 2020. The ‘biomineralization toolkit’ and the origin of animal skeletons. Biological Reviews Published online
Purnell, M.A., Donoghue, P.C.J., 1997. Architecture and functional morphology of the skeletal apparatus of ozarkodinid conodonts. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 352, 1545–1564