In the last quarter of the nineteenth century, an Argentine paleonthologist, Florentino Ameghino proposed a startling theory: man had originated in America, and, more precisely in the Argentine Pampas, from where he later spread out across the world.
He put this theory forth in the First International Americanist Congress held in Paris in 1879 .
According to Ameghino’s theory : the Miocene Period American apes, were forced by evolution to adapt to the Pampa’s prairies and walk on two feet, upright. They passed through several stages, from the most antique, the Tetraprothomo which evolved into the Triprothomo, who was followed by the Diprothomo and, finally, our ancestor, the “man of the Pampas”, Homo pampeanus who later crossing land bridges moved into the Old World.
Ameghino based his findings on stone tools, bones with evidence of human tampering and also evidence of man-made fires such as burned bones and fire hardened clay (which could not have been caused by natural fires due to the high temperatures required) which he found in sediments dating back over 3.5 Million years.
After visiting the Pampas and studying the findings in 1908, Czech - American anthropologist Alex Hrdlicka harshly refuted Ameghino’s theory, because he believed that the skeletons were actually intrusive burials (that migrated from new to old sediments) and that the specimens’ primitive traits fell within the limits of modern human variability and therefore belonged to modern natives. 
By the way, Hrdlicka was one of the promoters of the “immigration” theory, that is, that Asians peopled America crossing Beringia. Of course, Ameghino’s “authoctonist” theory and his were in direct conflict.
Even though modern findings have shown that man originated in Africa and from there moved on to conquer the world, we could interpret Ameghino’s findings in a different way: They were not the bones or remains of a local H. pampeanus, but of an ancient migration by H. erectus.
This could easily account for remains dating back to over 1.5 million years (though not for those older than that, as there were no hominds around more than 6 million years ago - Sahelanthropus thchadensis or, if we consider the australopithecines, not earlier than 4.5 million years).
Regarding the remains of hearths which cooked the soil beneath them, one scientific source states that these “would now be dated with an age close to one million years” .Who was around at that time and was capable of lighting a fire? Only one creature in the whole of the earth could do that:H. erectus. If so, and if the fires were man made, then H. erectus had to present in America.
Pliocene bone with an arrowhead
Then there is the famous toxodon (extinct megafaunal animal) femur bone with an arrowhead embedded in it. This was dated to the Late Pliocene some 2 – 3 million years ago. It was found at Miramar, on the Atlantic coast of Buenos Aires province. After Florentino Ameghino's death, by his brother Carlos, who carried on with his work. The image below shows the femur:
Though some have discredited it as a hoax, one of Ameghino's critics, Romero (1915) believed that the arrowhead had been placed there by an Indian from a later period who used the bone as a tool. Somehow the tool later got itself buried in older strata and this led to it being dated as Late Pliocene. 
Borman (1921)on the other hand, though he could not prove it, believed it was a hoax , and suspected that Parodi, who worked for the Museum, had somehow stuck the arrowhead in an old fossil toxodon bone and later “discovered” it. Of course, he did not produce any evidence to prove that Parodi had ever behaved fraudulently.
The question is open.
 Ameghino, F., (1879). L'homme prehistorique dans La Plata. Revue d'Anthropologie 2:210-249.
 Ameghino, F., (1880). La antiguedad del hombre en La Plata. 2 vols. Privately published, Paris.
 Hrdlicka, A., (1912). Early man in South America. Bureau of American Ethnology Bulletin 52. Smithsonian Institution, Washington.
 Isabel Hernández, (1992). Los Indios de Argentina. Editorial Abya Yala pp.22
 Ameghino, Carlos, (1915). El fémur de Miramar, una prueba mas de la presencia del hombre en el Terciario de la República Argentina. Nota preliminar. Anales del Museo Nacional de Historia Natural de Buenos Aíres, Tomo XXVI, Buenos Aires, pp. 433/50, láminas XXV y XXVI.
 Romero, A. A., (1915). La obra de Ameghino. La importancia de los hallazgos paleolíticos de Chapalmalan (Miramar). Buenos Aíres.
 Boman, Eric, (1921). Los vestigios de industria humana encontrados en Miramar (República Argentina), y atribuidos a la época terciaria. Rev. Chilena de Historia y Geografía, vol. 39. 330/52.
Further reading on ancient remains:
González, Germiniano, (2004). Sudamérica: cuna de la humanidad?. Club Universitario (in Spanish).
Bonomo, Mariano, (2002). El Hombre Fósil de Miramar. Intersecciones antropol., Olavarría, n. 3, dic. 2002. (in Spanish).
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia2011 International Year of Forests Copyright 2009-2011 by Austin Whittall ©