As part of the Serenada informal gedenkschrift, here's a short thing about fossil sea cows known from Jamaica. I know she liked Jamaica but I am unsure on her love of large extinct sea creatures. They're not quite supernatural creatures but I hope they'll do.

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Super quick primer on aquatic mammals

In our modern oceans, there's three groups of aquatic mammals1: mammals that spend most of, or their entire, life in freshwater or marine waters. Pinnipeds (seals, sea lions, walruses) are a group of carnivorans (cats, dogs, and their relatives) which went semi-aquatic and can locomote on land and in sea. Here's a link to the ongoing Observation Deck weekly rundown on extant pinnipeds. Cetaceans (toothed and baleen whales) are a group of artiodactyls (even-toed hoofed mammals) which went completely aquatic, except for when they are found in space around the planet Magrathea. The third group of marine mammals are sirenians.

Who and where is Sirenia

Sirenians are the only group of aquatic mammals which are primarily herbivorous, making their informal name of "sea cows" completely reasonable. There are ideas that they may have been the real source for mermaid myths? Like humans, sirenians have fairly anterior mammary glands, so maybe someone saw a female sirenian feeding her young and thought that looked somewhat human? I dunno if I'm convinced by that argument. The closest modern relatives of sirenians are proboscideans (elephants) and hyracoids (hyraxes), and with a few other groups they make up a group of placental mammals named Afrotheria. Sirenians are a completely aquatic group which, much like cetaceans, have almost entirely lost the skeleton of their hindlimbs. See for instance this skeleton of an adult and juvenile manatee on display at The Museum of Osteology in Oklahoma City, Oklahoma.

Sirenians are today represented by four species. The West Indian manatee (Trichechus manatus) is known from the Gulf of Mexico, Caribbean Sea, and northern/northeastern coast of South America; if you have heard of manatees in Florida being ran into by motorboats, it was this species. The Amazonian manatee (Trichechus inunguis) is known from the Amazon Basin. The West African manatee (Trichechus senegalensis) is known from coastal and freshwater river systems of Western and Central Africa. The dugong (Dugong dugon) is known from multiple coastlines of East Africa, Southern Asia, and Australia, and apparently may have even lived in the Mediterranean within the past few thousand years.

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The extirpation (local extinction) of dugongs from the Mediterranean is a quick reminder that human influences on sirenians can be quite deadly to the sirenians. Sirenians had their species diversity dropped by 20% by humans within recent recorded history. When Stellar's sea cow (Hydrodamalis gigas) was described by Western natural historians in 1741, they recognized that it seemed to be fairly small in abundance and distribution; later research has shown that at that time both natural and anthropogenic influences had reduced its distribution. But by 1768, the entire remaining population of Stellar's sea cow had been hunted to death for food and oil. So it goes.

Jamaica: sort of named the manatee and has oldest known sirenians

The word manatee itself may be a derivation of the word manatí from the Taíno people, who were the inhabitants of Jamaica in 1494 when Columbus and other explorers for Spain made landfall there. Since then, at least two fossil species of sirenians have been described from Jamaica. If there's more, I'm not ignoring them on purpose, I promise.

Prorastomus sirenoides

Mr. Henry H. Shirley sent Professor Richard Owen, at the Natural History Museum of London, a partial skull of a fairly manatee-looking creature. In an 1855 record in The Quarterly Journal of the Geological Society of London Owen's brief description of the fossil was given, along with a name, which referred to the boat's prow-shaped mouth of the creature. Owen later (1875) discussed a few more details of the skull and gave his opinion that this specimen was probably the oldest known sirenian; modern workers identify the fossil as being early middle Eocene in age, roughly 50 million years in age. Savage and colleagues (1994) described a newer specimen with fragments of skull, vertebrae, and ribs, and redescribed the material that Owen had described, after the skull had been prepared further. The image above is a very speculative one, because no limb elements for this species have been found; maybe it had reduced hindlimbs, we're not sure. But for another species we do have a fairly complete skeleton, and it's majestic.

Pezosiren portelli

A different, possibly slightly younger, western Jamaican early middle Eocene locality was discovered in 1990 by Roger W. Portell. The locality was worked on by crews from the University of the West Indies, Florida Museum of Natural History, and Smithsonian Museum. In addition to molluscs, a lizard, a possible primate, and a rhinoceros, this locality produced an almost complete skeleton of a new sirenian. Named by Domning in 2001, Pezosiren portelli, Portell's walking siren, was a 2.1 meter long … well, walking sirenian. It had four limbs capable of terrestrial motion, but its hyperdense ribs and retracted nasal opening are suggestive of an aquatic lifestyle. Most of that reconstructed skeleton above is based on real material. The bones of the hands and feet and most of the tail are speculative, but the rest of that is real awesome walking sea cow.

TL;DR

Pezosiren portelli was a land sea cow. Prorastomus sirenoides needs more material, go invest in Jamaican paleontology so we can find more of it. Jamaica's fossil sea cows are great, thank you Jamaica for such great fossils.

Citations and other end material

Domning DP. 2001. The earliest known fully quadrupedal sirenian. Nature 413:625-627.

Owen R. 1855. On the fossil skull of a mammal (Prorastomus sirenoides, Owen), from the island of Jamaica. Quarterly Journal of the Geological Society of London 11:541-543. Link to Google eBook which includes that.

Owen R. 1875. On Prorastomus sirenoides (Ow.). – Part II. Quarterly Journal of the Geological Society of London 31:559-567.

Savage RJG, Domning DP, Thewissen JGM. 1994. Fossil Sirenia of the West Atlantic and Caribbean region. V. Prorastomus sirenoides Owen, 1855. Journal of Vertebrate Paleontology 14(3):427-449.

1 Aquatic mammals are also called marine mammals, because they primarily are found in marine environments. … But not all of them are, particularly among sirenians, so I'm using the less commonly used term 'aquatic mammals' here.

Images courtesy of: I have no idea who made the top gif, calmingmanatee.com (apparently this is a meme-ification of an image uploaded to Wikimedia by Ahodges7), Wikimedia user Sklmsta, Nobu Tamura, uploaded by Wikimedia user ArthurWeasley, Wikimedia user Thesupermat.