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

Thepaleontologicallocalityof Achiri is located in the Bolivian Department of La Paz. It wasdiscoveredattheendofthe 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 Trachycalyptoidesachirense (Cingulata) andXyophorusvillaroeli(Tardigrada). Recent research has improved ourknowledgeofthislocality. Ten nearly completeskullsofPlesiotypotheriumwill allow diagnosing precisely P.achirenseandP.majusand identifying their affinities to other Mesotheriidae, while isolatedremainsof 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 chinchillidProlagostomussp. document rodents. The cingulate association encompasses the glyptodont Trachycalyptoides, the dasypodidChorobates,and the pampatheriid Kraglievichia.Slothsare diversified, with an early scelidotheriine (largerthanProscelidodon),ahuge mylodontine,newremainsofthepeculiar nothrotheriid of uncertain affinities Xyophorus,andasmall megatheriinesimilarinsizetoMegathericulus. 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 ~500mbelowitandmoreremote,yieldednotoungulate,rodent,andcingulateremains.Themostremarkablespecimenisanelongatedandlong-snoutedskullofahaplodontheriinetoxodontid,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 theevolutionofvertebrates throughout the ?middle-late Miocene period incentralBolivia.Thedetailedstudyofthesefaunas,coupledwithnewfieldmissions,willallowcorrelationwithdepositsfarthersouth(CerdasandQuebradaHonda,Bolivia;Maimara,Argentina)andnorth(LaVenta, Colombia;Acre,Brazil;Urumaco,Venezuela).