Anatomical Adaptions

 The elephant presents a unique characteristic in which the pleural membrane is thickened and the pleural cavity is eradicated by connective tissue (West et al., 2003). This unique set of anatomy came to be because elephants can snorkel in deep waters, this behavior suggests that micro vessels in the partial pleura are evident (West et al., 2003). Based on early onset of a thick parietal pleura in the elephant fetus, scientists have hypothesized that the development of the pleura is in response to the elephant's aquatic ancestors West et al., 2003).

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Embryological and paleontological  studies show that the elephants and sea cows must share a common ancestor (Gaeth et al., 1999).  The extinct 

Desmostylia appreared to have been semi aquatic, considering that they have only been found in marine deposits and maintained a herbivorous diet, feeding mainly on marine algae and angiosperms (Gaeth et al., 1999). Remains of Anthracobune, the earliest known elephant ancestor (50 million years ago), were found  in parts of Asian and Africa near shallow water environments (Gaeth et al., 1999). There are also similarities in enamel structure, most likely due to the similar diets that elephants and their ancestors had (Gaeth et al., 1999). Biochemical data also supports this theory by linking the two through the development of the fetal membrane (Gaeth et al., 1999). In addition to these findings, Gaeth et al. (1999) hypothesizes that the development of nephrostomes in the kidney, intra-abdominal location of the testes, and the premature developments could have all been adaptations to an aquatic lifestyle (Gaeth et al., 1999). 

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Nephrostomes, a feature most common in aquatic vertebrates such as sturgeons and frogs, have been found in the mesonephric kidneys throughout all stages of development in elephants (Gaeth et al., 1999). The presence of neprhostomes in the mesonephros of the elephant fetus could be a result of the slow embryonic and fetal development (Gaeth et al., 1999). There has never been any data collection recorded of nephrostomes in the mesonephric kidneys of other viviparous animals on land, demonstrating that the elephant may have evolved from an aquatic animal (Gaeth et al., 1999).

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Another unique characteristic of the elephant is the intra-abdominal location of its testes (Gaeth et al., 1999). The differentiation of the urogenital system in male African elephant fetuses heeded the typical mammalian pattern, except that testes remained intra-abdominal and never descended to the scrotum (Gaeth et al., 1999). In scrotal mammals, the testes descend and are guided by the the inguinal canal to the scrotum by the gubernaculum (Gaeth et al., 1999). During the process of fetal development in elephants, there was no evidence of a gubernaculum, scrotum, or inguinal canal (Gaeth et al., 1999). As a result, the scientists were able to conclude that the elephant was a primary testicond mammal (Gaeth et al., 1999).

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The trunk was evident in the earliest stages of fetus development, insinuating that the trunk must have been one of the first adaptations to an aquatic environment (Gaeth et al., 1999). A normal pleural cavity was present in all of the fetuses however, the parietal and visceral pleura fuse prior to birth, resulting in no pleural cavity (Gaeth et al., 1999).  By means of evolution, the parietal and visceral pleura were replaced with dense connective tissue and separation of the pleura by loose connective tissue also allowed for sliding movement (West, 2001). This adaptation was thought to be a form of protection against high negative intrathoracic pressures which occurs when water is sucked up while drinking (Gaeth et al., 1999). 

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As commonly reported by many scientists, dating all the way back to Aristotle (4th Century BCE), elephants in the wild can snorkel through their trunks while completely submerged underwater (West, 2001). Snorkeling at any depth can cause an increased amount of pressure differentials around the lung resulting in tissue perfusion (West, 2001). It is well established that when pressure surrounding large veins outside the thoracic cavity is high and atrial pressure is low, the veins are compressed while entering the thoracic cavity resulting in a independent venous return of the downstream pressure in the thoracic cavity (West, 2001). This phenomena protects the right atrium from filling up (West, 2001).

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