Cranial palaeopathologies in a Late Cretaceous mosasaur from the Netherlands

Here we describe multiple pathological skeletal elements in a specimen assigned to a globidensine mosasaur as Prognathodon cf. sectorius. This individual, NHMM 2012 072, was recovered from the upper Lixhe 3 Member (Gulpen Formation, upper Maastrichtian) near Maastricht, the Netherlands. Various injuries are visible on the anterior sections of the premaxillary, left maxillary and left dentary. In all likelihood, it was bitten in the snout by a large, possibly conspecific mosasaur – and survived this attack. The specimen described here is among the very few with clear and unambiguous evidence of (very likely intraspecific) agonistic interactions amongst mosasaurs. Despite significant injuries, including partial amputation of the premaxilla, this animal initially recuperated from the encounter, but the subsequent infectious processes as a result of this attack were still ongoing at the time of death. As a result, a vast amount of bone is dissolved in the maxillary, creating multiple anteroposteriorly oriented tubules and even starting to affect the enamel of the first maxillary tooth base. Radiological and morphological features suggest chronic osteomyelitis which probably hampered its ability to feed, potentially contributing to its demise. The underlying nature of such an encounter between two (or more) proportionally similar mosasaurs is highly speculative. However, the identification of more such encounters in the fossil record, suggests either intra- or interspecific competition or predation. According to the size of the victim and the suggested attacker(s), the latter would appear unlikely. Surprisingly, the specific immune response of this mosasaur to the chronic infection seems to hint at differences relative to the typical response of extant analogues including snakes.
This case study illustrates the potential of integrative three-dimensional approaches in palaeopathological studies to provide a much more comprehensive and detailed description of alterations and underlying physiological processes. Ideally pathological studies should aim to incorporate both histological and radiological techniques (including 3D-visualizations) to supplement traditional external morphological descriptions as suggested by previous authors. This allows for a much higher degree of certainty in identifying a causative factor, as well as providing a much more detailed description of skeletal processes on a tissue level.