Osteo-histology of Mesozoic marine tetrapods : implications for longevity, growth strategies and growth rates
Sammanfattning: Osteo-histology provides information on age, growth strategies, and lifestyles of both recent and ancient animals. This study deals with the histology of fossilized bone from three groups of tetrapods – sea turtles, ichthyosaurs and plesiosaurs – all secondarily adapted to marine life, but with rather different bone microstructures. As a result of extensive vascularization (i.e. osteoporosis), ichthyosaur bone is light, which may have contributed to increased manoeuvrability in open waters. This structure is comparable to that of most extant whales and dolphins. Plesiosaur bone, on the other hand, is very dense (i.e. pachyosteosclerotic) and therefore heavy. This extra weight may have been used for ballasting in a near-shore, shallow marine environment, indicative of habits similar to those of modern sirenians. Sea turtles display a lamellar, moderately vascularized bone pattern comparable to that of most recent turtles and crocodiles. This structure also indicates relatively slower growth rates compared to those of ichthyosaurs. The maturity of the animals at hand has also been investigated, and the sea turtle is adult, displaying at least 17 annual growth rings, whereas the ichthyosaur is a young adult or late juvenile and the plesiosaur is immature.
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