Manatees belong to one genus, Trichechus. It is made up by three species: one living along the southeastern coast of the US, the Central and South American coast along the Caribean. Another lives in the Amazon and Orinoco Rivers and a third one, on the shores of Senegal, in Western Africa.
They are big aquatic mammals measuring over 4 m (12 feet) long and weighing more than 1,000 kg (2,200 lb.). They graze the grasses and plants that grow in the river beds.
Their have adapted well to their aquatic environment: their front limbs have flattened into webbed flippers and they have a flat - single lobed dorsal tail. Their body is streamlined and they are excellent swimmers, capable of staying under water for over 15 minutes. Nevertheless, they are not capable of moving on land. 
The Amazon manatee is exclusively a fresh water creature, the others live in sat water and freshwater. All live in warm waters, from the Equator to roughly 20° from it.
Could these placid animals explain the "lake creature" sightings in Patagonia such as the "lake bulls"? Today's post will look into this question.
South American home to ancient Manatees
Manatee remains have been found in Argentina, along the banks of the Paraná River. They have been dated to the Upper Miocene (see my post on Miocene Americas)
These remains belong to the Rigodon limbatus a genus of the extant Trichechus manatees; it lived in the Upper Tertiary, and very likely belongs to the filogenetic line that leads to the modern Trichechus manatees.
The genus was first described by Florentino Ameghino in 1883 based on an upper molar found embedded in the clary cliffs along the shores of the Paraná River. He originally thought it may belong to a genus of the Tapiridae family, but after checking other molars he correctly identified them as belonging to a Sirenid -Sirenids span not only manatees but their relatives, the dugongs- in 1892 (he believed it to belong to the familiy of the Halitheridae, but we now know that they were Trichechidae.) 
Florentino Ameghino (1854-1911) was an anthropologist, zoologist and paleontologist. In 1886, he worked as Secretary and Sub-Director of the La Plata Museum. Between 1902 and 1911 he was Director of the Buenos Aires National Museum. Together with his brother Carlos he secured a large collection of Patagonian fossils and transformed South American geological studies.
He firmly believed humans had evolved in America and dispersed to the rest of the world from here. He also belived that extant mylodons could be found in Patagonia. He was a controversial scientist, yet many of his discoveries have proved sound.
Nowadays there are no manatees in the River Plate Basin, which comprises a large portion of southern South America spanning Brazil, Paraguay,Uruguay, Bolivia and Argentina, including the Paraná, Paraguay and Uruguay Rivers.
Could they have lived there until recently? An article written in 1899 seems to confirm this idea. It was written by Florencio de Basaldúa, an Argentine government official:
"While I was on a tour of duty for the National Government in the Territory of Misiones, I heard that Left Tennant Basualdo, subdelegate at the Port of Santo Tomé, on the shores of the upper Uruguay River, on the border with Brazil, reported to the General Ports Commander the existence of a great amphibian monster, whose lair was in a deep pool, close to his post. He believed it to be a hippopotamus, which the Brazilians living along the shore called mio-cao," [Bold mine] "because they had seen it swim in the river and graze on its shores, assuring that it was not Danta, Anta or Gran Bestia, common in that area" [Great Beast, all these names refer to the Tapir]. "And was not similar to any other animal that lives in those regions... 
Of course, we are well aware that hippopotami only live in Africa, and we imagine Basaldúa knew that too. So when he later met Florentino Ameghino and jokingly told him about this creature. Ameghino told him not to laugh about that story,and mendioned that in the past Augusto Bravard had reported a creature, the Manatus of the Paraná and Uruguay rivers, similar to the Manatee or sea cow of the Amazon.
This does not mean that Bravard actually saw one, it is more likely that he found bones or teeth. More research is needed on this point.
Interestingly, the creature mentioned by Basaldua as a Mio-Cao is a well known South American cryptid. It is the Minhocao or "Giant Earthworm". A snake-like being measuring 50 m (150 ft.) long and 5 m (15 ft.) wide.
However, being so big and, based on the description below, it is not something that one would identify with a Manatee. Perhaps Basaldúa used the wrong name to describe it.
The Minhocao's body is covered with scales, its skin is armored. It has a pig-like snout. Being a worm it lives underground but, is also amphibious. It burrows deep, attacks animals while they are crossing rivers and turns boats over. It knocks down trees, undermines roads and is found across the southern Amazon, southern Brazil and Uruguay.
All of these features are very unlike those of the placid grass munching manatee. Surely Minhocao and manatee are not the same creature. But the grazing bulky aquatic animal mentioned by Basaldúa is quite similar to a manatee.
Manatees, some extinct species
Manatees are endangered species, hunted for their blubber and meat, and accidentally hit by water craft and hurt by propellers, they are under pressure.
In a previous post, I mentioned another sirenid, a variety of manatee (Stller's sea cow) which lived in the North Pacific Ocean, close to Alaska and the Aleutian Islands and was hunted to extinction. I also conjectured about a possible "Sea Cow" in the South Pacific Coast of Chile.
There was also another manatee that lived on Saint Helena Island in the mid South Atlantic Ocean. These manatees were killed by the locals for their oil. The last sighting took place in 1810.
St. Helena is a tropical island located in the South Atlantic Ocean, about 1,950 km (1,210 mi.) from Africa and 2,900 km (1,800 mi.) from South America.
However, at the island's Manatee Bay -suggestive name indeed- manatee sightings have been reported recently .
An article printed in 1873 stated that in the early 1800s they were very abundant on the island: "at the beginning of this century the Manati or Manatee Sea cow or Sea lion existed in such numbers as to furnish employment for a fishery on it" [St. Helena Island] .
Yet, in the next paragraph it surmises that it was most likely a seal and not a manatee. Other authors belive it was a seal too (see:Theodor Mortensen, 1933).
Seals eat fish, manatees graze on sea grass and sea weeds... St. Helena island has over 60 marine algae and one species of red algae (Predaea feldmannii) is reported to be endemic. Close to the shore, at the base of the cliffs, there " is rock with a coating of seaweed and molluscs" , that means that there was food for them.
So here we have a possible sea-going manatee in the mid Atlantic. Could it have also dwelled along the South Atlantic coast? There is plenty of kelp in that area, enough to support a large manatee population. The cold water would not have been a problem (Steller's sea cow dealt with it in the freezing Alaskan waters).
Manatees and hippopotamus in Chile
We have information that there were manatees in Southern Chile: they are mentioned by Father Juan Ignacio Molina, the first European naturalist to describe Chilean animals in his book “Essay On The Natural History Of Chile” (1810) :
"In the Araucanian seas certain animals known as Sea Cows can sometimes be seen by its inhabitants; I could not assure if they are Lamantines or Rosmars, [walrus] or if they belong to another genus. According to the fuzzy description that they have given me, I am more inclined to believe that they belong to the species of the Trichecus Manatee. The first Spanirds who settled the large island of Juan Fernández captured a large quantity of such animals, on whose meat they joyfully fed; but the continuous killing that went on, has forced them to abandon the island's shores. 
Molina also mentions a variety hippopotamus in Chile, though he is cautious about it being a real creature (see my post on this): 
"The hippopotamus of rivers and lakes of the Araucan country, different to the African and similar in height and shape to the land horse but with palmed feet like those of seals. The existence of this animal is universally believed in, all over the country, and there are people […] who say they have seen its skin, which, they say, is covered with soft hair, of a color similar to that of tiny sea wolves."
Molina's is a very strange hippo; its soft fur makes it very different from the hair-less African variety. Also, its palmed feet differ from the hippo’s sturdy toes.
Historian José Toribio Medina mentions hippos en Chile in 1878: "I did not have the chance to see the sea horse. Based on the description of those who have seen it under water, I did not think that it was different to the African hippopotamus. Later, others who have seen it out of the sea, have told me that has the height of an ordinary horse, which it resembles in its head, tail and back, that its feet are like those of the seals, webbed." 
Toribio Medina's and Molina's descriptions are quite similar, but the animal they refer to is not a manatee, it is another type of beast, though what it is, will remain a mystery.
Getting back to our "sea cows", if there were sea cows on the Pacific Ocean seabord, and in St. Helena island, were there any along the Patagonian Atlantic coast?
Assuming that there were, could these creatures have swam upstream (along the Negro, Neuquén, Limay, Chubut, Senguer, Santa Cruz Rivers) towards the Patagonian Andean lakes, and originate the "Lake Bull" myths?
I am reading old sources to find refrences about sea cows in the South Atlantic Ocean. Who knows, we might find some surprises hidden in ancient texts.
 Rosendo Pascual, (1953). Sobre nuevos restos de Sirénidos del Mesopotamiense. Asociacion Geologica Argetina pp. 167. VIII No. 3, July 1953.
 Florencio de Basaldua, (1899), Monstruos Argentinos, Caras y Caretas II No. 32. May 13, 1899
 Lynas Murdoch, (2010). Four Years on St Helena. AuthorHouse, pp 82.
 Andrew Murray, Dec. 17, 1868. On the Geographical Relations of the Chief Colepterous Faunae. The Journal of the Linnean Society of London. vol 11, 1873 pp 16.
 Molina, J., (1986). Ensayo sobre la historia Natural de Chile. Santiago: Ediciones Maule. pp. 266
 Toribio Medina, J., (1878). Colección de historiadores de Chile y documentos.... vol 11
 G. C. Retching. Letters to Editor. Nature 138, 33-34 (04 July 1936), doi:10.1038/138033b0. The Manatee of St. Helena
 St Helena cle - JNCC. Defra.gov.uk
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia Copyright 2009-2014 by Austin Whittall ©