FIRST RECORD OF COXOFEMORAL DYSPLASIA IN A LATE TRIASSIC RYNCHOSAUR. Paleopathology deals with diseases that have left evidence in the fossil record. This field includes the identification of the pathology, and its consequences that on the animal that suffered it. We present the first record of a coxofemoral dysplasia in an Upper Triassic rhynchosaur, being also the first identification of this pathology in the fossil record. The specimen is an incomplete skeleton, partially articulated, of Hyperodapedon sanjuanensis (Sill), from the Ischigualasto Formation (Carnian—Norian). Rhynchosaurs were herbivores with a widespread geographical distribution, low species diversity and a stratigraphic range restricted to Triassic outcrops. The abnormalities described consist of atrophy of the sacrum and pelvis, sclerosed structures in some dorsal vertebrae, and deformation of the left femur. These features are presently characteristic of acetabular dysplasia in dogs. Acetabular dysplasia is a multifactorial disease appearing in the earliest stages of development and increasing throughout life, triggering a secondary joint osteoarthritis in the adult animal and leading to total disability of the affected limb. The advanced stage of the disease affecting the studied specimen reveals a pace known as “fourth grade claudication”, stage in which the affected limb stops supporting the body-weight, moving the center of gravity and loading the body-weight onto the other legs. Finally, the adult stage reached by the specimen —despite the severity of their condition— may suggest complex survival strategies in Hyperodapedon sanjuanensis, which need confirmation by future analyses.
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