Cretaceous dinosaurs liked spas: affinities of neosauropod nesting-sites with hydrothermal paleoenvironments

L.E. FIORELLI; G. GRELLET-TINNER; P.H. ALASINO; E. ARGAÑARAZ

San Luis

Jornada; XXV Jornadas Argentinas de Paleontologia de Vertebrados; 2010

Facultad de Cs. Físico-Matemáticas y Naturales, UNSL

Although several Late Cretaceous dinosaurs nesting sites have been discovered world-wide, the biological and paleoenvironmental triggers behind the selection of these nesting localities, have not yet been adequately investigated. Thus the factors that influenced the choice of selected colonial nesting sites by neosauropods still remain enigmatic. Herein we report for first time the stunning Sanagasta colonial nesting site in La Rioja Province, Argentina, a Cretaceous hydrothermal setting where a group of neosauropod dinosaurs came repetitively to ovideposit and specifically use the soil thermoradiance to incubate their eggs. Discovery of this new colonial nesting locality demonstrates nest fidelity over a long time and a symbiotic relationship between egg clutches and a peculiar hydrothermal environment that favored their incubation. Geochemical analyses, regional tectonisms, and field observations support a Cretaceous dating and synchronicity between the hydrothermal and nesting activities. This paleobehavior still is expressed in a few species of modern dinosaurs, namely the Polynesian megapode that buries its eggs in burrows at volcanically heated nesting sites. The Sanagasta discovery also implies associated migrations for reproduction and demonstrates a high dependency between reproductive characters/behaviors and a particular Cretaceous geological setting. Therefore, the selection of specific nesting site is an important element in the paleobiology of these sauropods and perhaps could have played a key role in their progressive extinction due to rapid environmental changes by the end of the Cretaceous.