FIRST REPORT OF A SKELETAL PATHOLOGY OF A MOSASAUR FROM THE SOUTHERN HEMISPHERE

TALEVI MARIANELLA; ROTHSCHILD BRUCE; FERNÁNDEZ, MARTA S.; REGUERO MARCELO; MITIDIERI, MATÍAS

Simposio; Xlll International Symposium on Antarctic Earth Sciences; 2019

Paleopathological studies have been used to understand the history of injuries and diseases in extinct forms. Examples of paleopathologies have been widely observed and recognized among fossil vertebrates, including dinosaurs and various marine reptiles. Paleopathology studies represent a vast field of novel information in etiological terms and insight to resulting limitations affecting behaviour and provide a glimpse of the possible survival strategies under which these reptiles lived. Infections are a well-recognized complication of injuries, as noted in dinosaurs and marine reptiles, with joint infections specifically noted in shoulders of pliosaurs. Spondyloarthropathy has been previously recognized as pan-phylogenetic in mammals and as isolated phenomenon in Dimetrodon, Diadectes, Ctenorhachis, mosasaurs, hadrosaurs, ceratopsia. It is predominantly vertebral in distribution, although peripheral joints have sometimes been affected. Northern Patagonia and the Antarctic Peninsula have rich records of Upper Cretaceous (Campanian and Maastrichtian) marine reptiles. However paleopathology?s have not been previously reported from in these abundant and diverse marine reptile assemblages. We describe a left scapula belonging to a juvenile mosasaurs (Plioplatecarpinae, indet.) from the López de Bertodano Formation (upper Maastrichtian) of Marambio Island (Seymour Island), Antarctic Peninsula, representing the first report of a skeletal pathology of a mosasaur from the southern hemisphere. Macroscopic examination of the scapula revealed a remodelled, deeply excavated and expanded gleno-humeral joint with adjacent linear disruption. X-ray examination revealed a deep excavation expanding the glenoid fossa, with disorganized subchondral bone and a focal spherical defect. The diagnostic considerations are infectious arthritis and spondyloarthropathy. The former is characterized by erosions with reactive new bone formation, the latter, by disorganized trabecular patterns underlying the articular surface. The spheroid defect recognized radiologically and presences of the surface defect (indicative of a draining sinus) are parsimonious with the diagnosis of infectious arthritis. The articulation of the scapula and humerus was disrupted by the glenoid fossa expansion, compromising its normal function as a fulcrum. The limb was thus rendered flail, unable to contribute to propulsion or directionality (steering). The individual survived long enough for partial healing, in the form of new bone formation. This process may occur as rapidly as within a few days in mammals, but commonly is more prolonged (e.g., month) in reptiles. However given the high growth rate and endothermic of hydropelvic mosasaurs, new bone deposition may have occurred much faster than in extant squamates. The individual did not continue to grow for a long time after the appearance of the lesion. Although not directly related to the mosasaur death, this condition may have contributed to the demise of the animal by reducing its effectiveness at obtaining food or increasing susceptibility to fatal disease, additional injury, or even predation. A juvenile mosasaur with this condition would eventually make it an easy prey.