EARLY PLATYRRHINE AND CAVIOMORPH BIOGEOGRAPHY: EMERGING EVIDENCE FROM THE AMAZONIAN RIVER BASINS OF PERU HIGHLIGHT THE ROLE OF THE TROPICS

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

Congreso; Congreso de la Asociación Paleontológica Argentina; 2021

While the modern intertropical regions of South America are among the most biodiverse in the world, their vertebrate fossilrecord is dominated by high-latitude localities obscuring the earliest appearance and radiations of platyrrhine primatesand caviomorph rodents. Recent discoveries in the Amazonian region of Peru have uncovered new localities spanning the?middle Eocene?late Miocene/Pliocene. These records offer novel insight into the first appearance of these groups. Herewe provide an update of occurrence data for these taxa, including previously undescribed findings and associated newdetrital zircon dates. The oldest well-dated records of South American primates are from the Peruvian Santa Rosa locality.These include a stem platyrrhine, Perupithecus, and a parapithecid stem anthropoid, Ucayalipithecus, belonging to a groupotherwise restricted to Africa. Recent absolute dates on Santa Rosa indicate an early Oligocene age. Fragmentary primateremains at Shapaja may be ~33 Ma but the age is not radiometrically confirmed. The next youngest platyrrhine isCanaanimico, a distinct soriacebine from CTA-61 of Contamana (26.5 Ma). Later, platyrrhines from the late Oligocene?earlyMiocene are only known from mid- to high latitudes, with the exception of two low latitude records from the Río Alto Madrede Dios: a small talus of uncertain affinity and an isolated tooth assigned to Parvimico (18.9?17.1 Ma). The oldestcaviomorphs have been recovered from the same localities, as well as others proposed to be of middle?late Eocene toearly Oligocene age (CTA-27 and CTA-29 of Contamana, Balsayacu, and Juanjui). These assemblages are diverse, withalmost all taxa having primitive dental characters (brachydonty, bunolophodonty, and quadrangular teeth). Accordingly,Cachiyacuy, Canaanimys, and Eosallamys paulacoutoi from CTA-27 and Santa Rosa have been argued to have plesiomorphicmolar morphologies, similar to the earliest Afro-Asian hystricognaths. However, some rodents at Santa Rosa and Shapajahave derived molar patterns (Eoincamys, Eodelphomys). We further include two new early Oligocene localities from Río AltoMadre de Dios tributaries: Río Carbón (31.87 ± 0.08 Ma) and Río Aguaroa (30.28±0.74 Ma). While taxonomic analysis isongoing, fossils appear similar to Pozomys, Cachiyacuy, and Eobranisamys, primitive forms described from Contamana andSanta Rosa. The current Peruvian data support a possible ~10 Ma interval separating the earliest caviomorphs fromplatyrrhines. After their arrival to South America, caviomorphs immediately diversified into their four major superfamilies;yet a few primitive forms appear both resilient and widespread, occurring at Contamana, Santa Rosa, Río Carbón, and RíoAguaroa. There is no evidence for crown platyrrhines among the tropical fossils from the early Oligocene?early Miocene,but the homunculid subfamily Soriacebinae?well-represented in Patagonia during the early?middle Miocene?wasalready present in the tropics by the late Oligocene. With one fossil primate assigned to an otherwise exclusively Africanradiation and caviomorphs directly related with an African hystricognath (Eoincamys), evidence is mounting for severalwestward Paleogene transatlantic crossings in the late Eocene?early Oligocene. Current evidence from the South AmericanPaleogene tropical fossil record indicates the tropics were a cradle, generating the mammalian diversity sampled from laterPatagonian localities.