Late Cretaceous reptilian biota of the La Colonia Formation, central Patagonia, Argentina: Occurrences, preservation and paleoenvironments Zulma Gasparini a, b , Juliana Sterli b, c, * , Ana Parras b, d , Jos  e Patricio O'Gorman a, b , Leonardo Salgado b, e , Julio Varela d , Diego Pol b, c a Divisi on Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata, Paseo del Bosque s/n, B1900FWA La Plata, Argentina b CONICET: Consejo Nacional de Investigaciones Científicas y T ecnicas, Argentina c Museo Paleontol ogico Egidio Feruglio, Av. Fontana 140, 9100 Trelew, Chubut, Argentina d INCITAP (CONICET-UNLPam), Facultad de Ciencias Exactas y Naturales, Universidad Nacional de La Pampa, Uruguay 151, 6300 Santa Rosa, La Pampa, Argentina e Instituto de Investigaci on en Paleobiología y Geología, Universidad Nacional de Río Negro, Isidro Lobo y Belgrano, 8332 General Roca, Argentina article info Article history: Received 28 July 2014 Accepted in revised form 2 November 2014 Available online Keywords: Late Cretaceous reptiles Central Patagonia Systematics Paleoenvironments abstract Cropping out on the southeastern margin of the Somún Cur a Plateau, the La Colonia Formation (Cam- panianeMaastrichtian) has yielded, over the last several decades, a varied fossil tetrapod fauna (mam- mals, ophidians, turtles, dinosaurs, plesiosaurs, anurans). For this study several field trips were carried out specifically to recover reptile remains. Three sections, located on the southeastern slope of the Sierra de La Colonia and in the vicinity of Cerro Bayo, Chubut Province (Argentina), were selected for particular attention. The prospected sections are composed of massive, laminated or heterolithic siltstones and claystones, with scarce and thin intercalations of massive, heterolithic o cross-bedded fine sandstones and of fossiliferous conglomerates. The most abundantly recovered reptiles are terrestrial and freshwater turtles, followed by plesiosaurs and dinosaurs. Among the chelonians, more than 16 specimens of Patagoniaemys gasparinae (Meiolaniformes), three specimens of Yaminuechelys aff. Y. gasparinii (Cheli- dae), and the remains of a new genus of Chelidae were identified. Among the dinosaurs, theropod metatarsal fragments, an incomplete abelisaurid theropod skeleton, sauropod vertebrae, ankylosaur osteoderms and appendicular fragments of hadrosaurs were found. Among the plesiosaurs there are several well preserved elasmosaurids (including two with associated gastroliths) and a polycotylid (Sulcusuchus erraini). Except for the plesiosaurs, all the reptiles are terrestrial or freshwater taxa. How- ever, analysis of the elasmosaurids indicates they are adult specimens of small body size, which could be related to forms that lived in restricted aquatic environments. Likewise, the polycotylid possesses deep rostral and mandibular grooves, and a conspicuous vascularization and/or innervation, that is consistent with the presence of some associated special sensory structures similar to those known in some ceta- ceans that inhabit modern rivers and estuaries. Sedimentological analysis suggests that deposition would have been mostly in low-energy restricted environments, like muddy plains, marshes and ponds cut by meandering channels, probably in the central mixed-energy zone within an estuary. This interpretation is consistent with the habitat inferred for the recovered reptiles, as well as with associated foraminifers and with the probable origin of gastroliths found associate with the plesiosaurs. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction During the Late Cretaceous and up into the Danian, wide areas of extra Andean Patagonia were covered by the Atlantic Ocean. This transgression, the first Atlantic transgression recognized in Patagonia, exceeded the extent reached by subsequent Atlantic * Corresponding author. Museo Paleontol ogico Egidio Feruglio, Av. Fontana 140, 9100 Trelew, Chubut, Argentina. Tel.: þ54 280 443 2100. E-mail addresses: zgaspari@fcnym.unlp.edu.ar (Z. Gasparini), jsterli@mef.org.ar (J. Sterli), aparras@exactas.unlpam.edu.ar (A. Parras), joseogorman@fcnym.unlp. edu.ar (J.P. O'Gorman), lsalgado@unrn.edu.ar (L. Salgado), julioadrianvarela@ hotmail.com (J. Varela), dpol@mef.org.ar (D. Pol). Contents lists available at ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes http://dx.doi.org/10.1016/j.cretres.2014.11.010 0195-6671/© 2014 Elsevier Ltd. All rights reserved. Cretaceous Research 54 (2015) 154e168