FIRST EARLY MIOCENE CAVIOMORPH ASSEMBLAGE FROM LOW LATITUDES OF SOUTH AMERICA

GONZALES, LAUREN A.; ARNAL MICHELLE; VALDIVIA A. L.; MORSE, PAUL E.; BORTHS, MATTHEW R.; FLEMING, PERRY R.; MARTÍNEZ, JEAN- NOËL; KAY, RICHARD F.

Congreso; SVP Annual Meeting; 2021

Caviomorpha are hystricognath rodents endemic to SouthAmerica. Their rich fossil record indicates an arrival onthe continent during the Paleogene, followed by adaptiveradiation into the higher latitudes of Patagonia during theNeogene. To date, however, the best record ofcaviomorph diversity, paleobiology, and evolution isrestricted to high-latitude localities with a paucity ofinformation from the low-latitude tropics. Here, from sitesin Peru, we describe the first tropical record ofcaviomorphs from the early Miocene.Fossils were collected from Site AMD-45, located in theBala Fm. of the Madre de Dios Basin (13°S) along theRío Alto Madre de Dios. Dates from detrital zirconsconstrain the locality?s minimum depositional age to 17.1± 0.7 Ma, making this the only tropical fauna comparablein age to the oldest levels of the Santa Cruz Fm. ofPatagonian Argentina (Santacrucian) ranging 48?52oS. AtAMD-45, we recognize representatives of the four maincaviomorph clades: Chinchilloids are the most abundantand diverse group, with the presence of Scleromyspraecursor and at least three new taxa ranging from lowcrownedbrachydonty to euhypsodonty. Pan-Octodontoidsare also abundant but less diverse; they are represented byAcarechimys minutus, only known from Patagonia, a newbrachydont taxon similar to Acarechimys and Selvamys,and a new adelphomyine. Erethizontoids are representedby a new lineage similar to Protosteiromys. Cavioidea isthe least abundant clade, with one tooth recognized as?Luantus, also only known from Patagonia.Preliminary study indicates this rodent assemblage has itsgreatest taxonomic resemblance with those of lateOligocene levels of Contamana and early Oligocene ofShapaja (in Peru), and less resemblance with the middleMiocene of La Venta, Colombia. It extends the ranges ofat least two taxa previously known only from the earlyMiocene of Argentinean Patagonia. Most notable,however, is the observed diversity in crown height.Though we document several brachydont caviomorphs(Acarechimys minutus, Acarechimys sp. nov.,Erethizontoidea sp. nov.), many taxa are higher-crowned(Scleromys praecursor, ?Luantus, a new adelphomyine, alow-crowned chinchilloid) or even euhypsodont (newchinchilloid). These findings indicate an early Miocenerodent fauna with great morphological diversity andspecies richness, comparable to assemblages of higherlatitudes,and provide insight into the tropical radiationand evolution of caviomorphs.