A study led by scientists from the Natural History Museum of America try clarify whether dinosaurs were in decline long before their extinction at the end of the Cretaceous. The research team consists of a scientist associated with the Museum of Natural History, Steve Brusatte; by the director of the museum's Paleontology Division, Mark Norell; by the scientist of the Ludwig Maximilian University of Munich, Richard Butler; and by Albert Prieto-Márquez, from the State Collection of Paleontology in Bavaria. It is the first scientific approach to the extinction of dinosaurs based on morphological disparity, that is, the variation in body structure within a particular group of dinosaurs.
The conclusions were published on May 1 in the journal Nature and suggest that, in general, the huge herbivores were in decline during the last 12 million years of the Cretaceous. But carnivorous dinosaurs and medium-sized herbivores don't. Furthermore, in some cases, the geographical location could have been an influential factor in the biological success of the animal.
For Steve Brusatte, “few issues in the history of paleontology”They have pushed“as much research and popular fascination as the extinction of the dinosaurs”. The mystery about its extinction, which could be due to volcanic explosions or an asteroid, gives rise to a large number of theories. But the researchers are now trying to clarify if the catastrophe happened as they have always presented it or, if on the contrary, it is something inevitable.
Theories preceding the one presented by Brusatte's team were carried out almost exclusively in estimates of changes in the number of dinosaurs. However, the new approaches seek to be more thorough and precise.
“Looking only at trends in taxonomic diversity, one receives contradictory answers about the state of dinosaurs before extinction”Says Brusatte. "This is because the results may be biased by an unbalanced sample of the fossil records. In places where more rocks and fossils formed, such as the Great American Plains, more species would be found. We want to go beyond a simple species count”.
Scientists claim examine the change in biodiversity within a given group of dinosaurs over time, in order to create an estimated capture of the general welfare of the animals. Then, it would be determined that the groups that show an increase in the variations, could have evolved into more species, giving them an ecological advantage. On the other hand, the decrease in variations would be a sign of extinction in the long term. In any case, the researchers have isolated morphological disparities from the seven largest groups of dinosaurs, using databases that include features of all kinds on the intricate skeletal structure of about 150 different species.
Butler comments that dinosaurs they were "extremely diverse”. There were hundreds of species living in the Cretaceous and they differed enormously "in diet, shape and size”. The different groups were evolving unevenly, and that is what the result of the new study shows. Hadrosaurs and ceratopsids experienced a decline in biodiversity in the last 12 million years of Cretaceous.
As a counterpoint, small herbivores and carnivores remained relatively stable or they even increased their biodiversity, that is, even more species from these groups appeared. In addition, it must be taken into account that hadrosaurs show different levels of disparity depending on the place where they were located. While went into decline in North America, diversity increased in Asia during the Cretaceous.
“These disparity calculations create a more nuanced picture of the last 12 million years of dinosaur history.”Explains Brusatte. "Contrary to how things are perceived, the Cretaceous was not a static world that was violently disrupted by an asteroid or a natural catastrophe. Some dinosaurs were undergoing dramatic changes during this period and the large herbivores appeared to have entered a long-term decline, at least in North America.”.
In North America, extreme climatic and earthly fluctuations, could have affected the evolution of dinosaurs differently from species on other continents. Therefore, the authors are of the opinion that North American records they may not be representative of an overall pattern. They also point out that there is no way to argue whether a group of decaying dinosaurs would have survived if catastrophic extinction had not occurred.
However, they do comment on the relativity of your study. Norell reasons that although the disparity of some species of dinosaurs and regional fauna was “downhill”, This does not mean “automatically that dinosaurs were doomed to extinction”. The diversity of dinosaurs fluctuated throughout the Mesozoic and slight increases or decreases during time intervals are not relevant within the context of the 150 million year history of these animals.
Passionate about History, he has a degree in Journalism and Audiovisual Communication. Since he was little he loved history and ended up exploring the 18th, 19th and 20th centuries above all.