Archaeogaia macachaae gen. et sp. nov., one of the oldest Notoungulata Roth, 1903 from the early-middle Paleocene Mealla Formation (Central Andes, Argentina) with insights into the Paleocene-Eocene south American biochronology

ZIMICZ ANA N.; FERNANDEZ, MERCEDES; BOND, M.; CHORNOGUBSKY, LAURA; ARNAL, MICHELLE; CÁRDENAS MAGALÍ; FERNÍCOLA JUAN CARLOS

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2020

0895-9811

In this contribution, we report the discovery of Archaeogaia macachaae gen. et sp. nov., one of the oldestnotoungulate recovered from the upper section of Mealla Formation in the Tonco Valley (NorthwesternArgentina, Salta Province). The new material consists on a left mandibular fragment with damaged m1 andcomplete m2-3. Archaeogaia macachaae is characterized by the following combination of features: m1 slightlyshorter than m2 and both larger than m3; brachydont molars; talonid mesio-distally shorter than trigonid;metaconid slightly taller than protoconid and distally placed; reduced paraconid in m2; metalophid straight inm2?3, but it runs mesially forming a slightly obtuse angle in the labial edge in m2, whereas it is more transversein m3; transverse entolophid; mesial cingulid extending from the middle to the lingual face of molars; and distalcingulid connecting the hypoconulid with the mesial face of the entoconid on m2?3. We perform a phylogeneticanalysis based on a data matrix composed of 147 craniodental characters and 70 taxa. The analysis yields 6104most parsimonious trees of 423 steps each. In the strict consensus previously well-supported clades collapse intoa polytomy; and Archaeogaia is positioned within the order Notoungulata based on two synapomorphies: a)presence of a transverse entolophid, and b) lower cheek teeth with short mesio-distal protolophid, transversemetalophid and mesio-distal hypolophid slightly convex labially. The former character was recovered as a synapomorphy for Notoungulata in several previous studies. According to the reduced consensus, Archaeogaiaoccupies different positions within the order; these fluctuating locations could be the result of the presence ofplesiomorphic features in the holotype, and the absence of the structures that define the notoungulate clades inwhich the new taxon is located. The paleomagnetic data indicates that the Mealla Formation was depositedduring Chron 27r to the base of Chron 26r (latest Danian-earliest Selandian). In this context, we discuss thefinding of Archaeogaia, and the age of Mealla Formation in the South American biochronology.