Estudio de patologías óseas en reptiles marinos mesozoicos de Patagonia y Antártida

Abstract

Paleopathological studies have been used to understand the history of injuries and diseases in the fossil record, and allow deducing the type of skeletal damage that occurs in fossil specimens, its apparent cause, and aspects related to palaeoecology and behavior. The analysis of the pathological characteristics of the Mesozoic marine reptiles of Patagonia and Antarctica, is presented as a vast field of study still scarcely explored, and capable of offering novel information. The main objective of the work is to analyze bone elements of a plesiosaur and a mosasaur recovered from Patagonia and Antarctica which show signs of various paleopathologies. The elements of the specimens were analyzed macroscopically as well as by computerized microtomography. Also, through the photogrammetry technique, a 3D reconstruction of the elements was made, which were then printed using a 3D printer (Creality Ender 3). The first specimen (MML-PV 1305) consists of a cervical vertebra belonging to an adult plesiosaur, recovered from the upper Maastrichtian of Patagonia (Bajo de Santa Rosa, Río Negro). This represents the first report of a bone paleopathology in a marine reptile from Argentina. The macroscopic analysis revealed the presence of a Schmorl nodule accompanied by osteophytes on the lower left edge of the vertebral centrum on the anterior articular face. The analysis of the microtomographs revealed a depression in the central region of the vertebral centrum, followed by an erosion that extended internally to the middle region of it. All these characteristics observed in the specimen are consistent with the diagnosis of a mechanical stress trauma, generated by torsional and compression forces produced by the length of the neck itself or at feeding moments. This pathological condition could generate difficulties in movement and cause recurrent pain in the individual's cervical region. The second specimen (MLP 87-II-7-1) consists of a left scapula belonging to a juvenile mosasaur, recovered from the upper Maastrichtian of Antarctica (Marambio Island), which represents the first report of a bone pathology in a marine reptile from Antarctica . The macroscopic analysis revealed an expansion of the glenohumeral joint, which was deeply eroded and remodeled, and a draining sinus at the level of the scapular neck, which was surrounded by a thin margin of new periosteal bone. Microtomography analysis revealed disorganized trabecular tissue and two draining sinuses. All these characteristics observed in the specimen are consistent with the diagnosis of infectious arthritis. The joint of the scapula and humerus was interrupted by erosion of the glenoid fossa, compromising its normal function. Although not directly related to the death of the mosasaur, this condition may have contributed to reducing its effectiveness in obtaining food or increasing its susceptibility to fatal disease, additional injury, or even predation. The results obtained from the work complement the state of knowledge about current pathologies in extinct forms and their evolutionary prospecting, as well as paleoecological aspects of the organisms studied.