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 NATALIA; CHORNOGUBSKY, LAURA; FERNICOLA, JUAN CARLOS; BOND, MARIANO; FERNÁNDEZ, MERCEDES; CÁRDENAS, MAGALÍ; ARNAL, MICHELLE

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 103

0895-9811

In this contribution, we report the discovery of Archaeogaia macachaae gen. et sp. nov., oneof the oldest notoungulate recovered from the upper section of Mealla Formation in theTonco Valley (Northwestern Argentina, Salta Province). The new material consists on a leftmandibular fragment with damaged m1 and complete m2-3. Archaeogaia macachaae ischaracterized by the following combination of features: m1 slightly shorter than m2 and bothlarger than m3; brachydont molars; talonid mesio-distally shorter than trigonid; metaconidslightly taller than protoconid and distally placed; reduced paraconid in m2; metalophidstraight in m2?3, but it runs mesially forming a slightly obtuse angle in the labial edge in m2,whereas it is more transverse in m3; transverse entolophid; mesial cingulid extending fromthe middle to the lingual face of molars; and distal cingulid connecting the hypoconulid withthe mesial face of the entoconid on m2?3. We perform a phylogenetic analysis based on adata 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-supportedclades collapse into a polytomy; and Archaeogaia is positioned within the orderNotoungulata based on two synapomorphies: a) presence of a transverse entolophid, and b)lower cheek teeth with short mesio-distal protolophid, transverse metalophid and mesio-distalhypolophid slightly convex labially. The former character was recovered as a synapomorphyfor Notoungulata in several previous studies. According to the reduced consensus,Archaeogaia occupies different positions within the order; these fluctuating locations couldbe the result of the presence of plesiomorphic features in the holotype, and the absence of thestructures that define the notoungulate clades in which the new taxon is located. Thepaleomagnetic data indicates that the Mealla Formation was deposited during Chron 27r tothe 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 Americanbiochronology.