Application of Fracture Mechanics to Failure in Manatee Rib Bone

Developmental changes in bone mechanics from Florida manatees (Trichechus manatus latirostris), obligate swimming mammals

Mammals living in aquatic environments load their axial skeletons differently from their terrestrial counterparts. The structure and mechanical behavior of trabecular bone can be especially indicative of varying habitual forces. Here, we investigated vertebral trabecular bone mechanical properties (yield strength, stiffness and toughness) throughout development in Florida manatees (Trichechus manatus latirostris), obligate undulatory swimmers. Thoracic, lumbar and caudal vertebrae were dissected from manatees (N=20) during necropsies. We extracted 6 mm3 samples from vertebral bodies and tested them in compression in three orientations (rostrocaudal, dorsoventral and mediolateral) at 2 mm min-1 We determined variation in mechanical properties between sexes, and among developmental stages, vertebral regions and testing orientations. We also investigated the relationships between vertebral process lengths and properties of dorsoventrally and mediolaterally tested bone. Rostrocaudally tested bone was the strongest, stiffest and toughest, suggesting that this is the principal direction of stress. Our results showed that bone from female subadults was stronger and stiffer than that of their male counterparts; based on these data, we hypothesize that hormonal shifts at sexual maturity may partially drive these differences. In calves, bone from the posterior region was stronger and tougher than that from the anterior region. We hypothesize that as animals grow rapidly throughout early development, bone in the posterior region would be the most ossified to support the rostrocaudal force propagation associated with undulatory swimming.

Aquatic Habits of Cetacean Ancestors: Integrating Bone Microanatomy and Stable Isotopes

The earliest cetaceans were interpreted as semi-aquatic based on the presence of thickened bones and stable oxygen isotopes in tooth enamel. However, the origin of aquatic behaviors in cetacean relatives (e.g., raoellids, anthracotheres) remains unclear. This study reconstructs the origins of aquatic behaviors based on long bone microanatomy and stable oxygen isotopes of tooth enamel in modern and extinct cetartiodactylans. Our findings are congruent with published accounts that microanatomy can be a reliable indicator of aquatic behaviors in taxa that are obligatorily aquatic, and also highlight that some "semi-aquatic" behaviors (fleeing into the water to escape predation) may have a stronger relationship to bone microanatomy than others (herbivory in near-shore aquatic settings). Bone microanatomy is best considered with other lines of information in the land-to-sea transition of cetaceans, such as stable isotopes. This study extends our understanding of the progression of skeletal phenotypes associated with habitat shifts in the relatives of cetaceans.

Embarcações motorizadas: uma ameaça aos peixes-boi marinhos (Trichechus manatus) no Brasil

O aumento do tráfego de embarcações motorizadas em áreas utilizadas para alimentação, descanso e reprodução pelos peixes-boi marinhos tem não só afugentado estes animais, mas resultado em potenciais casos de colisões. Este trabalho tem como objetivo relatar casos de interações entre embarcações motorizadas e peixes-boi marinhos (Trichechus manatus) no litoral Nordeste do Brasil. As interações ocorreram nos Estados do Ceará, Paraíba e Sergipe com três espécimes, sendo um destes com quatro registros. Foram observados transtornos clínicos como edema da região frontal, proptose ocular, emagrecimento e múltiplos cortes ao longo do corpo. Sendo assim, o aumento do tráfego de embarcações, e a falta de normativas e de fiscalização que assegurem a efetiva proteção de determinadas áreas, representam um risco direto para a conservação dos peixes-boi marinhos no litoral Nordeste do Brasil.