BoletĂn del Museo Nacional de Historia Natural, Chile, 64: 69-79 (2015)
FIRST RECORD OF MOSASAURS (LEPIDOSAURIA: MOSASAURIDAE) FROM THE LATE CRETACEOUS (MAASTRICHTIAN) OF THE MAGALLANES BASIN SERGIO SOTO-ACUĂA (1,2), RODRIGO A. OTERO (1) y DAVID RUBILAR-ROGERS (2) (1) Red PaleontolĂłgica U-Chile, Laboratorio de Ontogenia y Filogenia, Departamento de BiologĂa, Facultad de Ciencias, Universidad de Chile. Las Palmeras 3425, Ăuñoa, Santiago de Chile; arcosaurio@gmail.com, otero2112@gmail.com (2) Ărea PaleontologĂa, Museo Nacional de Historia Natural, Casilla 787, Santiago de Chile; david.rubilar@mnhn.cl ABSTRACT Mosasaurs were a specialized clade of marine squamates with global distribution during the Upper Cretaceous and their presence is relatively frequent in Maastrichtian levels of Central Chile and Antarctica. However, until now, the group was absent in Cretaceous units from Southern Chile. Herein we report for the first time the presence of this clade in Upper Cretaceous levels of the Dorotea Formation, Magallanes Region. The material comprises a concretionary block with caudal vertebrae recovered from Sierra Dorotea, near Puerto Natales. Despite the fragmentary nature of the specimen, this record confirms the presence of mosasaurs in the Magallanes Basin, adding new taxa to the known local diversity of marine reptiles so far just represented by elasmosaurid plesiosaurs. This new record allows to making connections with the previous occurrences of mosasaurs from the James Ross Basin in Antarctica, adding new data to the marine herpetofauna in the Weddellian Biogeographic Province. Keyword: Mosasauridae, Maastrichtian, Biogeographic Weddellian Province
RESUMEN Primer registro de Mosasaurio (Lepidosauria: Mosasauridae) del CretĂĄcico TardĂo (Masstrichtiano) de la Cuenca de Magallanes. Los mosasaurios son un clado especializado de Squamata marinos de amplia distribuciĂłn global durante el CretĂĄcico superior y su presencia es relativamente frecuente en depĂłsitos marinos del Maastrichtiano de Chile Central y AntĂĄrtica, sin embargo, hasta ahora, el grupo estĂĄba ausente del registro fĂłsil en el extremo sur de Chile. AquĂ documentamos, por primera vez, la presencia del clado en niveles del CretĂĄcico Superior de la FormaciĂłn Dorotea, en la RegiĂłn de Magallanes. El material consiste en un bloque con vĂ©rtebras caudales recuperado en la localidad de Sierra Dorotea, en las cercanĂas de Puerto Natales. A pesar de la naturaleza fragmentaria del espĂ©cimen, el material permite confirmar la presencia de mosasaurios en la FormaciĂłn Dorotea, junto con la previamente conocida diversidad local de reptiles marinos hasta ahora representada por plesiosaurios elasmosĂĄuridos. Este nuevo registro permite establecer conexiones con existencias previas de mosasaurios de la Cuenca de James Ross en AntĂĄrtica, agregando nuevos datos para la herpetofauna compartida en la Provincia BiogeogrĂĄfica Wedelliana. Palabras clave: Mosasauridae, Maastrichtian, Biogeographic Weddellian Province
INTRODUCTION Mosasaurs (Squamata, Mosasauroidea) are a clade of aquatic lizards widely distributed along the Late Cretaceous seas, with a fossil record documented at least since the Cenomanian (Caldwell and Palci 2007, Bardet et al. 2008) until the upper Maastrichtian (Jagt 2005, Gallagher et al. 2012, Mulder et al. 2013). Inhabiting of epicontinentals seas and even of freshwater courses (MakĂĄdi et al. 2012), the mosasaurs have been found worldwide, including records from Antarctica (Novas et al. 2002, FernĂĄndez and Martin 2009). The traditional definition of âmosasaurâ involves characters such as the acquisition of hydrodynamic adaptions of the skeleton, derived from a terrestrial ancestral condition that includes deep modifications of the vertebrae, limbs and pelvic girdle (Russell 1967), as well as the bony microanatomy (Houssaye et al. 2013), the integument (Lindgren et al. 2011) and the presence of heterocercal fin tail (Lindgren et al. 2013). However, some of these novelties were acquired independently in different mosasaur lineages (Bell and Polcyn 2005, Caldwell and Palci 2007, Caldwell 2012).