Palaeoecological inferences about dinosaur gregarious behaviour based on the study of tracksites from La Rioja area in the Cameros Basin (Lower Cretaceous, Spain)

Abstract

In La Rioja the widespread ichnological record of dinosaurs ranges from the Berriasian to the Aptian age (Early Cretaceous). There, due to the high palaeodiversity, several evidences of gregarious behaviour can be observed in different types of footprints (sauropods, theropods and ornithopods). Moreover, due to the huge dimensions of some sites, different types of dinosaur tracks representing gregarious behaviour can be found very close in space and time. All these evidences have been compiled and analysed, obtaining an overview of this type of behaviour in relation to the type of trackmaker. Twenty-eight evidences of gregariousness have been found, of which nine are of sauropod footprints, twelve of theropod, seven of ornithopod, and one of unknown bipedal dinosaurs. These data have been further divided into accumulations and sets of parallel trackways. In sauropod footprints the main evidence is represented by the accumulations of tracks made by herds of individuals of the same size. In ornithopod footprints there are accumulations and parallel trackways of large size individuals and even family groups. In theropod footprints, sets of parallel trackways of few individuals of the same size (from small to medium) are the most common evidence and there are no data about gregariousness in large theropod footprints. Thus, data were obtained on different sizes of herds, size of individuals and structure of the groups depending on different ichnotypes, providing information about important palaeoecological aspects of their trackmakers, such as population structure.Keywords: dinosaurs, footprints, gregarious behaviour, Cretaceous, La Rioja, Spain Resumen En La Rioja existe un abundante registro icnológico de dinosaurios en materiales de edades Berriasiense-Aptiense (Cretácico Inferior). En ellos se pueden observar diferentes muestras de comportamiento gregario en distintos tipos de huellas (saurópodas, terópodas y ornitópodas). Incluso debido al gran tamaño de algunos yacimientos, se pueden encontrar muestras de comportamiento gregario de distintos tipos de dinosaurios muy próximas en el espacio y en el tiempo. Se han recopilado todas estas evidencias y se han analizado para obtener así una visión global de este tipo de comportamiento en funcion de los dinosaurios que las produjeron. Se ha obtenido un total de veintiocho evidencias de gregarismo, de las cuales nueve son de icnitas saurópodas, doce de terópodas, siete de ornitópodas y una de dinosaurios bípedos indeterminados. Todas estas evidencias se han dividido en acumulaciones y conjuntos de rastros paralelos. En icnitas saurópodas se observan fundamentalmente acumulaciones de huellas atribuidas a manadas constituidas todas por individuos de talla media. En cuanto a icnitas ornitópodas, hay acumulaciones y conjuntos de rastros paralelos de individuos de gran tamaño así como grupos familiares de pocos individuos. En icnitas terópodas se observan más evidencias de conjuntos de rastros paralelos con individuos generalmente de talla semejante (pequeña a median...

Ichnological evidence of Megalosaurid Dinosaurs Crossing Middle Jurassic Tidal Flats

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Multi-aged social behaviour based on artiodactyl tracks in an early Miocene palustrine wetland (Ebro Basin, Spain)

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