Thursday, 20 June 2013

An aquatic past for elephants

Endotheliochorial placenta of the Amazonian manatee
Fetal (fc) and maternal (mc) capillaries are present

The closest relatives to elephants are the dugong and manatees. Placentation in the African elephant Loxodonta africana has been well studied (reviewed here). We were able to show strong resemblances in the placenta and fetal membranes between the elephant and the Amazonian manatee Trichecus inunguis (here).

This hoax photo of the Loch Ness monster
is thought to be an elephant swimming

It has long been suspected that the ancestor of proboscideans was aquatic or semi-aquatic (here). Clues include the presence of nephrostomes in the mesonephros of the fetus (here). Now support comes from an unexpected quarter: myoglobin.

Diving mammals such as whales and seals have high amounts of myoglobin in their muscles to act as a source of oxygen during prolonged submersion. A new study (here) shows that in such species there is an increase in surface charge of the molecule to prevent dimerization occurring at high concentrations of myoglobin. This molecular signature was also found in sirenians and proboscideans. The analysis included two extinct species: the woolly mammoth (previous post) and Steller's sea cow. A phylogenetic analysis suggested that substitutions contributing to increased surface charge on myoglobin occurred in the common ancestor of sea cows, elephants and hyraxes (paenungulates). The conclusion drawn is that this ancestor may have been semiaquatic.

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