When I was in Mexico, in the year of our Lord one thousand five hundred eighty six, they found one of those giants buried in one of our farms, which we call Jesus del Monte, of whom they brought a tooth to be seen, which (without augmenting) was as big as the fist of a man; and, according to this, all the rest was proportionate, which I saw and admired at his deformed greatness. (Book VII, adapted from the Grimston translation of 1604)
Isn’t that cute? I think it should be obvious what is happening here. Acosta is reporting the discovery of a large prehistoric tooth, almost certainly one of a mastodon, mammoth, or other member of the paleomegafauna. In fact, an examination of the known finds of mastodon fossils and the habitation zone of the semi-mythical Chichimeca finds that they overlap as far south as Puebla, Mexico, the southernmost point of the known mastodon range, and near the southernmost range of the nomads who passed under the name Chichimeca. Similarly, the bones of “incredible bigness” must be mastodon bones, which as late as the eighteenth century were still confusing scholars into thinking they belonged to giants.
Acosta’s tooth almost exactly parallels the tooth seen by Gov. Dudley of Massachusetts in 1705 and declared by him to be that of a Biblical giant (Genesis 6:4) killed in the Flood, for he was “perfectly of opinion that the tooth will agree only to a human body, for whom the flood only could prepare a funeral; and, without doubt, he waded as long as he could keep his head above the clouds, but must, at length, be confounded with all other creatures.” The tooth is today a known mastodon tooth.