Osseous and other hard tissue pathologies in turtles and abnormalities of mineral deposition

Abstract

Actualistic interpretation (on the basis of disorders documented in life) of pathology in modern turtles, and across the phylogenetic spectrum, allows confident diagnosis of disease in fossil turtles. Fortunately, those diseases that affect bone do so in a manner that appears independent of phylogeny and even of geologic chronology. To date, most pathologies have been reported as isolated observations. Therefore the latter have been characterized and placed within the framework of recognized diseases and activities. Toward this end, we surveyed the literature, assessing reports in terms of contemporary definitions. Epidemiologic studies of pathology in turtles are rare, with the exception of frequency of anomalies and of avascular necrosis and recognition of diving behavior. Notation of avascular necrosis in 50% of Cretaceous turtles, limitation to marine turtles, and its gradual reduction over geologic time present a unique window into turtle behavior and their development of strategies that minimize its occurrence. Anomalies, typically thought of as representing mutations, whether inherited or de novo, may also provide insight to environmental conditions. While amphibians are often utilized as markers of environmental health, extrapolation to reptiles is also pertinent. Fractures imply behavior, such as falls or mating injuries. Bites and other forms of trauma appear to be the most common cause of bone infections by bacteria and fungi. The most common forms of arthritis are gout and infections, although calcium pyrophosphate crystal disease and osteoarthritis also have been reported. Calcium and urate bladder stones have been reported. Vitamin D deficiency is essentially a phenomenon of captive animals, but can complicate kidney disease. Hyperparathyroidism may occur as part of what is referred to as renal osteodystrophy or it may occur as an isolated phenomenon. Carapace and plastron anomalies may represent normal variation, disease, or possibly even phylogenetic differences. The etiology of shell pitting has been highly controversial, with bites, parasites, mixed bacterial and fungal infections, and even algae invoked as causative agents. While many reports of such alterations, as well as isolated or identified associated organisms, exist, there has not been a delineation of which mechanism is responsible for specific types of shell lesions, or even a working vocabulary for describing such lesions.