In several posts I have written about marine creatures from the Miocene Epoch (which spans from about 23.3 to 5.3 Million years ago). During this period the geography of South America was quite different from what it is nowadays. As the map above shows, vasts parts of the continent were submerged by marine ingressions due to higher sea levels. Some "islands" remained safe and dry (the highlands which comprised the Brazilian and Guyanan shields as well as the rising Proto Andes). All the rest was under water.
Submerged South America
During the mid Miociene, between 10 and 20 million years ago, the sea levels rose and reached a maximum level, some 30 to 40 m (100 - 130 ft.) above current sea levels about 14 million years ago.
Seawater flooded the interior of South America forming "epicontinental" seas. There is still some discussion regarding the exact extension of these seas and if they were all interconnected however the fact remains that most of the Amazon basin and the Paranáa River basin and the Pampas were under the sea.
Parts of Patagonia were submerged (Somuncuráa Plateau and the Deseado shield) kept dry.
This marine enviornment would have created new access routes for Northern Hemisphere sea-going mammals such as the ancestors of modern seals, manatees and walruses. We have already mentioned the 'Central American seaway" (left red arrow) through Panama which linked the Caribbean with the Pacific Ocean as a route for dispersion. But, as you can see in the map, another narrow seaway connected the Caribbean with the Pebesian Sea (right red arrow). From here these creatures could have moved east into the Amazon or South all the way down to Patagonia.
Could the marine creatures discovered in southern Peru and Northern Chile ('walruses', giant marine sloths and sea cows) have counterparts on the eastern side of the Andes? In fact, the amazonian manatee and all other manatees around the world are said to have originated in Colombia (from the potamosiren). One of the members of the American manatee family (Trichechidae), the ribodon could be found all the way from the coast of North Carolina in the U.S. to Argentina in the south.
The lack of fossils in this region which was formerly the coast of these ancient seas may be due to their placement on the eastern foothills of the Andes. An area which is covered by dense jungles in the north and central parts of South America and, in the whole area, by hundreds of feet of sediment deposited there by the rivers dragging soil from the constant erosion of the Andes.
Maybe future exploration may yield new fossils that could help clarify the origin of some of South American cryptids (and hopefully, Patagonian cryptids too).
Quizás futuras exploraciones resulten en nuevos fósiles que puedan explicar algunos de los criptidos sudamericanos (y patagónicos).
This seaway joining the Caribbean and the South Atlantic is worth deeper analysis from a cryptozoological viewpoint as a route for cryptid dispersion.
 Daryl P. Domning, (1982). Evolution of Manatees: A Speculative History.
Journal of Paleontology, vol. 56, No. 3 (May, 1982), pp. 599-619.
 Evolution of the Sirenia
 For the map:
Kirby M.X., Jones D.S., MacFadden B.J., (2008) Lower Miocene Stratigraphy along the Panama Canal and Its Bearing on the Central American Peninsula. PLoS ONE 3(7): e2791. doi:10.1371/journal.pone.0002791
Marengo, H.G., (2000). Rasgos micropaleontológicos de los depósitos de la transgresión Entrerriense-Paranense en la cuenca Chaco-Paranense y noroeste argentino, República Argentina. En: F.G. Aceñolaza y R. Herbst (eds.), El Neógeno de Argentina. Serie Correlación Geológica 14: 29-45.
Alonso, Ricardo N., (1999). El terciario de la Puna salte˜ña In: Congreso Geológico Argentino, 1999, Salta. Relatorio XIV congreso geológico argentino, tomo I. , 1954. p.311 – 316.
Bush, Mark B., and Oliveira, Paulo E. de, (2006). The rise and fall of the Refugial Hypothesis of Amazonian speciation: a paleoecological perspective. Biota Neotrop., vol.6, n.1. ISSN 1676-0603. doi: 10.1590/S1676-06032006000100002.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia2010 International Year of Biodiversity Copyright 2009-2010 by Austin Whittall ©