The Miocene vertebrate faunas of Achiri, Bolivia

FRANÇOIS, PUJOS; PIERRE-OLIVIER, ANTOINE; BERNARDINO, MAMANI QUISPE; ABELLO, ALEJANDRA; ANDRADE FLORES, RUBEN

Raleigh

Congreso; 72nd Annual Meeting of the Society of Vertebrate Paleontology; 2012

The Society of Vertebrate Paleontology

The paleontological locality of Achiri is located in the Bolivian Department of La Paz. It was discovered at the end of the 1960s but it was not until the mid-1970s that it became the subject of intense studies. The fossiliferous levels of the typical locality, located hundreds of meters above the Ulloma Toba, are dated between 10.35 Ma (40Ar/39Ar, at Jankho Jakke Alto) and 8 Ma (K-Ar, west of San Andrés de Machaca). Several late Miocene mammals were identified in the last decades: the metatherian hathliacynid Borhyaenidium altiplanicum, the notoungulates Plesiotypotherium achirense and P. majus (Mesotheriidae) and Hoffstetterius imperator (Toxodontidae), the xenarthrans Trachycalyptoides achirense (Cingulata) and Xyophorus villaroeli (Tardigrada). Recent research has improved our knowledge of this locality. Ten nearly complete skulls of Plesiotypotherium will allow diagnosing precisely P. achirense and P. majus and identifying their affinities to other Mesotheriidae, while isolated remains of the typothere Hemihegetotherium expand the notoungulate assemblage. A Macraucheniidae litoptern isalso recognized. A new large hystricognath dinomyid, a medium-sized octodontoid, two cavioids (a cardiomyine and a dolichotine), and the chinchillid Prolagostomus sp. document rodents. The cingulate association encompasses the glyptodont Trachycalyptoides, the dasypodid Chorobates, and the pampatheriid Kraglievichia. Sloths are diversified, with an early scelidotheriine (larger than Proscelidodon), a huge mylodontine, new remains of the peculiar nothrotheriid of uncertain affinities Xyophorus, and a small megatheriine similar in size to Megathericulus. Field exploration in 2010-2011 resulted in the discovery of two older levels, stratigraphically older than the classical locality. The upper one, with amphibians, birds, and rodents, testifies to the presence of a lacustrine environment prior to the deposition of the latter (located ~200m above it in the same section). The lowermost one, located ~500m below it and more remote,yielded notoungulate, rodent, and cingulate remains. The most remarkable specimen is an elongated and long-snouted skull of a haplodontheriine toxodontid, with a complete dental formula (3I-C-4P-3M). The recognition of three successive fossiliferous levels nearly Achiri, the unexpected diversity of the concerned assembleages, and the exceptional preservation of the vertebrate remains are much promising as regard the evolution of vertebrates throughout the ?middle-late Miocene period in central Bolivia. The detailed study of these faunas, coupled with new field missions, will allow correlation with deposits farther south(Cerdas and Quebrada Honda, Bolivia; Maimara, Argentina) and north (LaVenta, Colombia; Acre, Brazil; Urumaco,Venezuela).