FIRST MAMMALIAN REMAIN FROM THE MIDDLE MIOCENE ANGASTACO FORMATION AT THE TONCO VALLEY, LOS CARDONES NATIONAL PARK, SALTA PROVINCE, ARGENTINA

1. FIRST MAMMALIAN REMAIN FROM THE MIDDLE MIOCENE ANGASTACO FORMATION AT THE
TONCO VALLEY, LOS CARDONES NATIONAL PARK, SALTA PROVINCE, ARGENTINA
1Instituto de Bio y Geociencias del Noroeste Argentino, Salta, Argentina 2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad Autónoma de Buenos Aires,
Argentina 3Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Ciudad Autónoma de Buenos Aires, Argentina 4Laboratorio de Anatomía
y Biología Evolutiva de los Vertebrados, Departamento de Ciencias Básicas, Universidad Nacional de Luján, Luján, Argentina
N. Zimicz1,2*, M. Fernández2,3,4, J.C. Fernicola2,3,4 and L. Chornogubsky2,3
The Tonco Valley is a synclinal structure of around 35 km located at the Calchaquíes Valleys (Salta Province, Northwestern Argentina). Almost
all the complete Cenozoic stratigraphic sequence outcrops along this valley. The Angastaco Formation (Payogastilla Group) comprises thick
fluvio-eolian Oligocene-Miocene deposits that record the regional environmental changes promoted by the Andean orogeny.

2. Angastaco Fm.
Palo Pintado Fm.
Here, we describe the first mammalian remain exhumed from the lower part of Las Flechas Member at the
Tonco Valley, Los Cardones National Park (Salta Province, Argentina). The age of the fossiliferous strata is
bracketed by absolute ages between 17.5 and 13.7 Ma (early-middle Miocene).
An arid paleoenvironment has been suggested for this unit based on geochemical data
and the alleged absence of fossils probably given by an oxidising depositional
environment.

3. The specimen IBIGEO-P 128 is an isolated hypselodont left upper molar (probably M1)
identified here as Hegetotheriinae indet. (Notoungulata, Typotheria, Hegetotheriidae). This
tooth is sub-trapezoidal in occlusal outline, being longer than wide; it exhibits a thick
cement layer. The enamel layer is continuous around the crown, being much thinner at the
mesio and disto-labial angles of the tooth; the labial face presents shallow, but conspicuous
grooves; the lingual face is slightly convex without entoflexus; the distal face is smooth, and
narrower than the remainder of the occlusal surface; the distal face and the ectoloph form an
angle of approximately 90°, and no fossettes are observed.
Systematic paleontology
Order NOTOUNGULATA Roth (1903)
Suborder TYPOTHERIA Zittel (1893)
Family HEGETOTHERIIDAE Ameghino (1894)
Subfamily HEGETOTHERIINAE Ameghino (1894)
Hegetotheriinae gen et sp. indet.
This report constitutes the earliest record of the family Hegetotheriidae in Northwestern
Argentina. The hypselodont condition of the specimen agrees with the suggested open
environments for the unit but demonstrates that the Angastaco Formation is fossiliferous and
the supposed absence of fossil remains is probably due to the previously low prospection
efforts.
This discovery emphasizes the need of exhaustive and systematic prospections in order to
understand the faunal configuration at the Central Andes during the Oligocene-Miocene.
FUNDING: ANPYCT, PICT201-0508 y PICT2019-3551; CONICET, IBIGEO-PUE y
PUE22920160100098; y UNLu PC-BC142-20.