Fossil localities of the Santa Cruz Formation (Early Miocene, Patagonia, Argentina) prospected by Carlos Ameghino in 1887 revisited and the location of the Notohippidian

Between January and September of 1887 Carlos Ameghino carried out his first geologic and paleontological expedition to the Rio Santa Cruz, Patagonia. Based on the fossils and geologic information compiled, in 1887 and 1889, Florentino Ameghino named more than 120 new species of extinct mammals and his Formacion Santacrucena and Piso Santacruceno (Santacrucian stage). Data published by both brothers state that the specimens were collected in outcrops by the Rio Santa Cruz, between 90 and 200 km west of its mouth. However, information in the posthumously published letters and Travel Diary of C. Ameghino allows us to recognize a fourth locality, Rio Bote, at about 50 km further southwest. In 1900, 1902, F. Ameghino divided the Piso Santacruceno in a younger etage Santacruzienne and older etage Notohippideen, restricting the geographical distribution of the latter to Kar Aiken locality, northeast of Lago Argentino. However, 15 of the 54 species that F. Ameghino listed as exclusively Notohippidian stage already had been named on specimens collected South to the Rio Santa Cruz in 1887, two year prior to C. Ameghino's first visit to Kar Aiken. Based on historical information and several expeditions to the Rio Santa Cruz and its environs, in this contribution we establish the geographical locations of the 1887 localities, formalize their names, evaluate the stratigraphic position of the fossil-bearing levels, and analyze the geographic extension of the Notohippidian, inferring that Rio Bote is where C. Ameghino first collected species that came to define the Notohippidian. (C) 2014 Elsevier Ltd. All rights reserved.