MINI-SERIES Ichthyosaurian palaeopathology: evidence of injury and disease in fossil ‘fish lizards’ J. M. Pardo-P erez 1,2 , B. P. Kear 3 , M. G omez 4 , M. Moroni 4 & E. E. Maxwell 1 1 Staatliches Museum f€ ur Naturkunde Stuttgart, Stuttgart, Germany 2 Vicerrector  ıa de Investigaci  on y Postgrado, Universidad de Magallanes, Punta Arenas, Chile 3 Museum of Evolution, Uppsala University, Uppsala, Sweden 4 Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Campus Isla Teja, Valdivia, Chile Keywords palaeobiology; ichthyosauria; Mesozoic; Reptilia; avascular necrosis; osteotrauma; palaeopathology. Correspondence Judith Pardo-P erez, Staatliches Museum f€ ur Naturkunde, Rosenstein 1, 70191 Stuttgart, Germany. Email: judith.pardo-perez@smns-bw.de Editor: Heike Lutermann Received 1 February 2017; revised 22 May 2017; accepted 13 June 2017 doi:10.1111/jzo.12517 Abstract The documented record of ichthyosaurian paleopathologies reveals an array of injury- related bone modifications and instances of disease evidenced through multiple clades, skeletal regions and body-size classes from the Middle Triassic to middle Cretaceous. Examples include traumatic injuries, as well as a high incidence of articular diseases, including avascular necrosis. Forelimb pathologies are particularly abundant (65% of total reported), and the glenoid region seems to have been especially prone to articular disease. In contrast, pathologies affecting the vertebral column are comparatively underrepresented (6% of reported pathologies). Also notable is the disproportionate commonality of osteopathologies in ichthyosaurian taxa between 2 and 6 m in length (54%), as opposed to demonstrably larger (31%) or smaller bodied (15%) species. Fur- thermore, osteopathologies are almost exclusively described from skeletally mature individuals, and are best known from taxa of Jurassic age (78%), versus those from the Triassic (15%) or Cretaceous (7%); this likely reflects biases in the ichthyosaurian fos- sil record through time. Ichthyosaurs evince remarkable similarities in the types of observed skeletal damage relative to other ecologically similar marine amniotes – espe- cially cetaceans and mosasaurid squamates, all of which potentially exhibited equiva- lent palaeoecological and/or behavioural adaptations for life in aqueous environments. Notably, however, the unusually low frequency of vertebral pathologies in ichthyo- saurs is peculiar, and requires further investigation to establish significance. Introduction Palaeopathological studies have been used to understand the his- tory of injury and disease in the fossil record (Rothschild & Mar- tin, 2006). They deduce the types of skeletal damage occurring in fossil populations, their underlying cause and by inference, aspects of related palaeoecology and behaviour (Moodie, 1918b; Rothschild & Martin, 2006). Palaeopathologies are usually iden- tified in fossil vertebrates only if they resulted in damage to the skeleton (but see, e.g., Rothschild & Depalma (2013), who reported traumatic skin damage in a hadrosaur) and are typically the result of a traumatic injury (e.g. fractures) involving bone modification and occasional callus development during healing. Infectious diseases can also develop after trauma (e.g. abscesses), or may be age related (e.g. osteoarthritis/osteoarthrosis) (Ling- ham-Soliar, 2004; Rothschild, 2012). Alternatively, osteological pathologies can result from other factors causing mechanical or physiological stress (Kompanje, 1999; Rothschild & Martin, 2006; Cooper & Dawson, 2009). Examples of putative palaeopathologies have long been observed among fossil vertebrates, and perhaps most famously among Mesozoic amniotes including dinosaurs and various marine reptiles (see Rothschild & Martin, 1993 for summary). Indeed, the latter have proven particularly pertinent for inter- preting lifestyle based on evidence of skeletal damage (e.g. bone modification attributed to nitrogen narcosis and diving habits: Rothschild & Martin, 1987; Rothschild, Xiaoting & Martin, 2012b; Rothschild, Schultze & Pellegrini, 2013). The earliest obligate marine amniotes were ichthyosaurs, which constituted a prolific radiation of middle to apex-level pelagic predators in Mesozoic aquatic ecosystems from the Early Triassic to the early Late Cretaceous (250–90 Ma) (McGowan & Motani, 2003; Dick & Maxwell, 2015). They were typified by a fish-like body plan with flipper-like fore- and hindlimbs; and relied primarily upon axial propulsion for subaqueous locomotion (McGowan & Motani, 2003). Unlike some other Mesozoic marine amniote clades (e.g. mosasaurid squamates), there is at present little compiled information describing the range and causes of osteopathologies observed in ichthyosaurs, although the frequency of avascular necrosis has been used as a key proxy for deep-diving behaviours (Motani, Rothschild & Wahl, 1999; Rothschild et al., 2012b). Journal of Zoology  (2017) – ª 2017 The Zoological Society of London 1 Journal of Zoology. Print ISSN 0952-8369