Extensive radial fibrolamellar bone tissue in long bones reveals an epidemic of persistent, recurrent, and non-traumatic bone infection in a juvenile-dominated phytosaur (Archosauria; Pseudosuchia) community.

We report for the first time an epidemic of persistent and recurrent bone infection in a Late Triassic juvenile-dominated phytosaur community. Bone histology of long limb bones and dorsal ribs of nine out of 21 individuals of Colossosuchus techniensis revealed aggressive periosteal growth as represented by distinct crescentic zone(s) of radial fibrolamellar bone tissue in the form of a sunburst pattern of the vascular channels and extensive secondary resorption at the mid- and outer cortical region. We propose that this Colossosuchus community suffered an epigenetic disease influenced by some exogenous factors and/or environments. The possibility of various diseases is reviewed, and within an extant phylogenetic bracketing approach, the most probable cause is inferred to be bacterial infection, especially in the form of osteomyelitis. Alternating occurrences of normal and diseased bone tissue in several limb bones, albeit in several individuals, suggest that the bone infection was persistent and recurrent, and resulted in a suppressed immunodefence system and restricted mobility that ultimately caused the demise of the phytosaur community.