Mary Anning’s marine reptiles: taxonomy, systematics, morphometrics and evolution of the iconic Ichthyosaurus
Ichthyosaurus is the most famous of all fossil marine reptiles, yet its taxonomy and composition is little studied. Hundreds of Ichthyosaurus specimens are known, and at least five species are recognized by recent authors. The autapomorphies and diagnosis of both Ichthyosaurus as a whole and its constituent species are little studied and several specimens reveal a range of intermediate conditions between currently recognized species. We report the most comprehensive analysis of Ichthyosaurus ever undertaken, based on a large sample of specimens (>200) from across the Lias. Precise data on the stratigraphic position of specimens is scant; one aim of this study is to use palynomorphs to establish age and provenance. This work has resulted in: (1) Anatomical clarification of the status of Ichthyosaurus; (2) Understanding of the likely species composition within Ichthyosaurus; (3) Large-scale morphometric, systematic and phylogenetic analyses within the clade, and; (4) A clear understanding of evolutionary trends within Ichthyosaurus across the Liassic. Conclusions indicate that the validity of Ichthyosaurus is supported by autapomorphies. However, specimen clusters recovered by principal-component (PC) and size-constrained PC morphometric analyses do not correspond to currently recognized species. Ichthyosaurus spans a range of body sizes and individuals cluster into several size classes. Some represent ontogenetic stages within species. Other clusters exhibit trends in body size evolution throughout the Lias. This work helps clarify both the true diversity and evolutionary history of this iconic Liassic animal, first brought to scientific attention by Mary Anning over a century ago.