Rodrigo Pellegrini

Microanatomical and Histological Features in the Long Bones of Mosasaurine Mosasaurs (Reptilia, Squamata) - Implications for Aquatic Adaptation and Growth Rates

Background During their evolution in the Late Cretaceous, mosasauroids attained a worldwide distribution, accompanied by a marked increase in body size and open ocean adaptations. This transition from land-dwellers to highly marine-adapted forms is readily apparent not only at the gross anatomic level but also in their inner bone architecture, which underwent profound modifications. Methodology/Principal Findings The present contribution describes, both qualitatively and quantitatively, the internal organization (microanatomy) and tissue types and characteristics (histology) of propodial and epipodial bones in one lineage of mosasauroids; i.e., the subfamily Mosasaurinae. By using microanatomical and histological data from limb bones in combination with recently acquired knowledge on the inner structure of ribs and vertebrae, and through comparisons with extant squamates and semi-aquatic to fully marine amniotes, we infer possible implications on mosasaurine evolution, aquatic adaptation, growth rates, and basal metabolic rates. Notably, we observe the occurrence of an unusual type of parallel-fibered bone, with large and randomly shaped osteocyte lacunae (otherwise typical of fibrous bone) and particular microanatomical features in Dallasaurus, which displays, rather than a spongious inner organization, bone mass increase in its humeri and a tubular organization in its femora and ribs. Conclusions/Significance The dominance of an unusual type of parallel-fibered bone suggests growth rates and, by extension, basal metabolic rates intermediate between that of the extant leatherback turtle, Dermochelys, and those suggested for plesiosaur and ichthyosaur reptiles. Moreover, the microanatomical features of the relatively primitive genus Dallasaurus differ from those of more derived mosasaurines, indicating an intermediate stage of adaptation for a marine existence. The more complete image of the various microanatomical trends observed in mosasaurine skeletal elements supports the evolutionary convergence between this lineage of secondarily aquatically adapted squamates and cetaceans in the ecological transition from a coastal to a pelagic lifestyle.

Osseous and Other Hard Tissue Pathologies in Turtles and Abnormalities of Mineral Deposition

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.

Summary of Osseous Pathology in Amphibians and Reptiles

The summary review of turtles is much more extensive than that currently possible for other reptiles and amphibians. The literature on the latter does not lend itself to such organization at this time. It consists mostly of isolated reports, with few epidemiological studies, predominantly representing a delineation of what has been noticed. Much of the discussed reptile analysis is derived from ongoing personal research.