Odontoceti's humerus: a novel study on its morphometry and bone density using helical CT

Abstract

Cetaceans are Mammals that have evolved through a series of morphophysiological adjustments of the various biological systems that allow them to live under water. One of them, the bone tissue is not fully understood and it is related both with the musculoskeletal and haematopoietic systems. From 2016 to date, humeri of 90 specimens belonging to 11 different species were collected from stranded animals in Canary Islands (Spain). Samples were analysed by means of helical computed tomography (CT), a technique particularly effective in the study of bone tissues, allowing measurements of bone densities. These have been measured from specific cross sections of the distal epiphysis, the diaphysis and the proximal epiphysis (separating the tubercle from the head of the humerus). Bone densities of the cortical and trabecular bone have been measured separately. Collected data led to trend plots focusing on the changes of the values along bones cross sections. Comparing these data, bone densities gradients showed a similar behaviour in individuals of the same species according to growth of each animal. Moreover it was interesting to discover that animals with similar diving habits have similar plots, thus differentiating between shallow and deep divers: deep divers have lower bone densities in the range of 200-800 Hounsfield while shallow divers’s range between 400-1600. The objectives of this project are the anatomical description together with the morphometric and bone density studies of the Cetaceans’ humerus, to obtain reference values that could help in a classification of the degree of growth of the animals, based on their skeletal development. Moreover, these data could be used to support diagnoses of pathologies related to the bone tissue.