A remarkable assemblage of enantiornithine birds from the Late Cretaceous of southeastern Brazil.

LUIS CHIAPPE; NAVA, WILLIAM R.; AGUSTIN MARTINELLI; RYAN TUCKER; HERCULANO ALVARENGA

Congreso; 78th Annual Meeting, Society of Vertebrate Paleontology,; 2018

Despite abundant discoveries of Mesozoic birds in recent decades, knowledge of theirevolution during the last 20 million years of the Cretaceous remains scant. However, thistime interval is essential to better understand the rise of modern birds and the pattern ofavifaunal turnover during the Cretaceous-Paleogene transition. We report on a remarkablyrich site (William?s Quarry; discovered in 2004 by WN) contained in the Upper CretaceousAdamantina Formation (Bauru Group) of southeastern Brazil (Presidente Prudente,western São Paulo State). Excavations at this site have produced hundreds of isolated andpartially articulated remains of small to medium-sized enantiornithine birds concentratedin a very small area (approximately 6 m2) of red-pink fluvial sandstones and claystones.Representing at least three taxa, the remains include numerous postcranial elements as wellas many skull portions (isolated rostra, mandibles, and crania) preserved in threedimensions. As the most abundant avian Mesozoic locality in the Americas and the richestsite of Late Cretaceous age in the world, this site provides key information for contrastinghypotheses of avian diversification during the K-Pg transition and the earliest divergencesof modern birds. Along with other Late Cretaceous localities from Gondwana, theinformation revealed at this site indicates a clear abundance of enantiornithine bird speciesduring the ~80?70 mya interval. Such a record is difficult to reconcile with hypothesesarguing that modern (neornithine) birds originated in the southern hemisphere during theLate Cretaceous.