Biomedical Ephemera, or: A Frog for Your Boils

Top: Dorsal view and pectoral limb of Manatus americanus (now Trichechus manatus)
Bottom: African Elephant (Loxodonta africana)

These two creatures, though vastly different, are actually some of the most closely related extant sea and land mammalia.

Though the transition from land to sea occurred around the same time, the Sirenians (dugongs and manatees) are only distantly related to the Pinnipedia (seals and sea lions) and Cetacea (whales). The only living ocean-dwelling mammalian herbivores, Sirenians split off from a common ancestor with elephants around the middle of the Eocene epoch. This pig-like creature was very distinct from the small deer-like creatures that led to both the Cetaceans and modern horses.

The manatee’s land-dwelling origins can be seen in their pectoral limbs - there are “fingernails” at the end of each flipper, much more similar to the fingernails on an elephant’s foot than the claw-like nails you can see on the Pinnipedia.

Manatee: Transactions of the Zoological Society of London, Vol. VIII 1874.

Elephant: Wildlife of the World: A Descriptive Survey of the Geographical Distribution of Animals. Richard Lydekker, 1911.