UAB research confirms the extinction of dinosaurs was not a gradual process

18 March 2010
Universitat Autònoma de Barcelona

Researchers of the UAB Department of Geology, in collaboration with the Catalan Institute of Palaeontology (ICP), systematised data from 29 archaeological sites containing dinosaur bones, tracks and eggs located in the Catalan Pyrenees, one of the best areas of the world to study the period in which these animals went extinct. The research confirms that there was a large diversity of dinosaur species shortly before the moment in which they became extinct. This conclusion refutes scientific hypotheses defending that the catastrophe which caused the extinction of dinosaurs was only the final end of a more gradual process. In addition, researchers discovered the unexpected presence of a group of Asian dinosaurs which arrived only one million years before the species disappeared.

Dinosaurs became extinct 65 million years ago. In fact, the species which became extinct is what scientists name “non-avian” dinosaurs, given that some dinosaur descendants still exist: birds or “avian” dinosaurs. The cause was most probably due to several large meteors impacting with the planet. However, there is the belief that during the time of this catastrophe dinosaurs were already in decline, suffering from a gradual extinction process. To study the evolution of this phenomenon, researchers from all parts of the world search for and analyse dinosaur fossils from this period, known as the Maastrichtian, the last stage of the Cretaceous period. There are several sites in North America corresponding to this period. In the rest of the world however there are very few, and there is a need for global evidence of what happened before dinosaurs became extinct. One of the best areas of the world with which to compare data from North America is the southern part of the Pyrenees. The sites located in the towns of Tremp and Aren are rich in bones; those in Vallcebre contain many dinosaur tracks, and at Coll de Nargó many fossilised eggs can be found.

Violeta Riera, a young researcher at the UAB Department of Geology, worked in collaboration with Oriol Oms (UAB), Rodrigo Gaete (Conca Dellà Museum) and Àngel Galobart (Catalan Institute of Palaeontology) to carry out the first study focused on organising and establishing connections between fossils found at the 29 Pyrenean sites by systematising all data into a graphic diagram known to geologists as a correlation panel. The diagram directly shows to which period each of the remains from the different sites belong.

The main conclusion of the research is that at the end of the Maastrichtian stage there was a large diversity in dinosaur species. In the upper layers of the sediments, those corresponding to stages closest to the extinction period, researchers were able to observe this diversification. This fact collides head-on with the hypothesis that the extinction of dinosaurs was a gradual process.

The research also shows for the first time that the Sauropod titanosaurus (herbivorous quadrupeds reaching enormous sizes), as well as the nodosaurid (armoured herbivores), preferred swampy environments, while other dinosaurs such as the dromaeosaurid (relatively small-sized carnivores, closely related to birds) lived in practically all types of environments.

“Often it is very difficult to identify a specific species”, Violeta states, “since there are sites containing over 700 bones, but very few skull bones and these are the bones that we need to identify the species accurately.” Nevertheless, among the numerous classified fossils there are many bones belonging to the only species defined until now in Catalonia, two hadrosaurids or “duck-billed” dinosaurs, the Pararhabdodon isonensis and the Koutalisaurus kohleri (although it is thought that the two are most probably the same species).

The research revealed another surprising fact, the presence in the Pyrenees of a group of dinosaurs from Asia during the last one million years before extinction: the lambeosaurids, a group of hadrosaurids with empty crests differing in shape and size according to the species.

For Violeta Riera, studying dinosaurs in Catalonia is a privilege, given that “the dinosaurs found here are the last specimens which lived on Earth”. “The Pyrenees”, she affirms, “are the only place in Europe where quality research can be carried out on the period in which they became extinct”. No other European mountain range offers such rich sites since “at that time, Europe was a large archipelago with not much land for dinosaurs”. This is the first exhaustive research in all of Europe to be carried out on the period during which dinosaurs became extinct.

The research was published recently in the prestigious journal Palaeogeography, Palaeoclimatology, Palaeoecology.

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(Submitted by Tim Chapman)