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Since their appearance in the fossil record 34 Mya, modern cetaceans (dolphins, whales, and porpoises) have radiated into diverse habitats circumglobally, developing vast phenotypic variations among species. Traits such as skeletal morphology and ecologically-linked behaviors denote swimming activity; trade-offs in flexibility and rigidity along the vertebral column determine patterns of caudal oscillation. Here, we categorized 10 species of cetaceans (Families Delphinidae and Kogiidae; N = 21 animals) into functional groups based on vertebral centra morphology, swimming speeds, diving behavior, and inferred swimming patterns. We quantified trabecular bone mechanical properties (yield strength, apparent stiffness, and resilience) among functional groups and regions of the vertebral column (thoracic, lumbar, and caudal). 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. Overall, bone from the pre-fluke/fluke boundary had the greatest yield strength and resilience, indicating that the greatest forces are translated to the tail during caudal oscillatory swimming. Group 1, composed of five shallow-diving delphinid species, had the greatest vertebral trabecular bone yield strength, apparent stiffness, and resilience of all functional groups. Conversely, Group 3, composed of two deep-diving kogiid species, had the least strong, stiff, and resilient bone, while Group 2 (three deep-diving delphinid species) exhibited intermediate values. These data suggest that species that incorporate prolonged glides during deep descents in the water column actively swim less, and place relatively smaller loads on their vertebral columns, compared with species that execute shallower dives. We found that cetacean vertebral trabecular bone properties differed from the properties of terrestrial mammals; for every given bone strength, cetacean bone was less stiff by comparison. This relative lack of material rigidity within vertebral bone may be attributed to the non-weight bearing locomotor modes of fully aquatic mammals.
Since their appearance in the fossil record 34 Mya, modern cetaceans (dolphins, whales, and porpoises) have radiated into diverse habitats circumglobally, developing vast phenotypic variations among species. Traits such as skeletal morphology and ecologically-linked behaviors denote swimming activity; trade-offs in flexibility and rigidity along the vertebral column determine patterns of caudal oscillation. Here, we categorized 10 species of cetaceans (Families Delphinidae and Kogiidae; N = 21 animals) into functional groups based on vertebral centra morphology, swimming speeds, diving behavior, and inferred swimming patterns. We quantified trabecular bone mechanical properties (yield strength, apparent stiffness, and resilience) among functional groups and regions of the vertebral column (thoracic, lumbar, and caudal). 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. Overall, bone from the pre-fluke/fluke boundary had the greatest yield strength and resilience, indicating that the greatest forces are translated to the tail during caudal oscillatory swimming. Group 1, composed of five shallow-diving delphinid species, had the greatest vertebral trabecular bone yield strength, apparent stiffness, and resilience of all functional groups. Conversely, Group 3, composed of two deep-diving kogiid species, had the least strong, stiff, and resilient bone, while Group 2 (three deep-diving delphinid species) exhibited intermediate values. These data suggest that species that incorporate prolonged glides during deep descents in the water column actively swim less, and place relatively smaller loads on their vertebral columns, compared with species that execute shallower dives. We found that cetacean vertebral trabecular bone properties differed from the properties of terrestrial mammals; for every given bone strength, cetacean bone was less stiff by comparison. This relative lack of material rigidity within vertebral bone may be attributed to the non-weight bearing locomotor modes of fully aquatic mammals.
The knowledge of Mesoplodon peruvianus species about its distribution and ecology is limited, because the range of the species is unknown. Mainly due to their inconspicuous behaviour. A survey was conducted from November 2014 to January 2015 along a near 80 km long transect in the central coast of Oaxaca. Additionally, based on an stranded individual at Zicatela beach, we measured it and performed a necropsy to report the probable cause of stranding. Two individuals of M. peruvianus species were observed on December 5, 2014 at about 9.3 km from the coast at 12:45 local time. The identification was clearly positive because of the black and white large individual, with an estimated size of 4 m. This is the first record of M. peruvianus in the area. On March second 2016, a carcass of a male of M. peruvianus was found stranded at Zicatela beach; was classified as scale 2 stranded individual (freshly dead). Our main pathological findings were related with the respiratory and the digestive systems. The thoracic cavity arose out of air suggesting a pneumothorax; lungs were collapsed and to the touch showed a consistency of atelectasis. In total, 18 marine mammal species have been recorded for the state of Oaxaca, this study adds a new record, confirming the presence of M. peruvianus and its distribution in the region. The collapsed lungs of the stranded individual, probably resulted from an apnea state, were related with dysbarism. In Mexico no exist the practice of necropsies in wild marine mammals, therefore, our work contributes to gather relevant information on the health of marine mammals and the threats they face.El conocimiento acerca de la distribución y ecología de Mesoplodon peruvianus es limitada debido a que su comportamiento enigmático limita el conocimiento acerca de su ámbito hogareño. Se realizaron muestreos en transectos lineales paralelos a la costa de Oaxaca de noviembre de 2014 a enero de 2015 con el fin de obtener registros de mamíferos marinos. Adicionalmente, con base en un ejemplar varado en la playa Zicatela en 2016, realizamos su medición y necropsia para indagar las posibles causas del varamiento. Dos individuos de M. peruvianus fueron avistados el 5 de diciembre de 2014 a 9.3 km de la costa alrededor de las 12:45 horas del día. La identificación se realizó por la típica coloración y se le estimó una longitud de 4 m. Estos avistamientos son el primer registro de M. peruvianus en la zona, contribuyendo al conocimiento de la especie. El 2 de marzo de 2016, se encontró el cadáver de un ejemplar macho de M. peruvianus varado en la playa Zicatela. Se le clasificó en la escala 2 (recién muerto). Nuestros principales hallazgos patológicos se relacionaron con el sistema respiratorio y el digestivo. La cavidad toracica presentó evidencia de aire sugiriendo un pneumotorax y los pulmones estuvieron colapsados y al tacto presentaron una consistencia elástica atribuida a una posible atelectasia. En total, 18 especies de mamíferos marinos han sido registrados para el estado de Oaxaca y nuestro trabajo adic...
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