Ichthyosaurian palaeopathology: evidence of injury and disease in fossil ‘fish lizards’

• Published in: Journal of zoology (1987) Vol. 304; no. 1; pp. 21 - 33
• Main Authors: Pardo‐Pérez, J. M., Kear, B. P., Gómez, M., Moroni, M., Maxwell, E. E.
• Format: Journal Article
• Language: English
• Published: London Blackwell Publishing Ltd 01-01-2018
• Subjects: Adaptation; Aqueous environments; Avascular necrosis; Biocompatibility; Biomedical materials; Body size; Commonality; Cretaceous; Disease; Diseases; Fish; Fossils; ichthyosauria; Injuries; Jurassic; Lizards; Marine ecology; Mesozoic; Necrosis; osteotrauma; palaeobiology; Palaeoecology; palaeopathology; Reptilia; Taxa; Triassic; Vertebrae; Wounds
• ISSN: 0952-8369; 1469-7998; 1469-7998
• DOI: 10.1111/jzo.12517

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. Furthermore, 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 fossil record through time. Ichthyosaurs evince remarkable similarities in the types of observed skeletal damage relative to other ecologically similar marine amniotes – especially cetaceans and mosasaurid squamates, all of which potentially exhibited equivalent palaeoecological and/or behavioural adaptations for life in aqueous environments. Notably, however, the unusually low frequency of vertebral pathologies in ichthyosaurs is peculiar, and requires further investigation to establish significance.
The recorded ichthyosaurian paleopathologies reveals a series of injury‐related bone modifications and diseases evidenced in different species, skeletal regions and body‐size classes during the Mesozoic. Traumatic injuries as a high incidence of articular diseases are the most documented. Particularly abundant are pathologies from the forefin (65%), in contrast to pathologies affecting the vertebral column (6%). Pathologies in ichthyosaurs are almost exclusively described from mature individuals and are most abundant in Jurassic age taxa (78%) than those from the Triassic (15%) or Cretaceous (7%). The pathologies documented in ichthyosaurs evidence remarkable similarities to the ones observed in ecologically similar marine amniotes, specially cetaceans and mosasaurs, exhibiting a potential palaeoecological and/or behavioural equivalent adaptations for life in marine environments.