66 million years ago, terrestrial dinosaurs succumbed to the impact of a huge asteroid that fell on the Yucatan Peninsula (Mexico). The cataclysm wiped them out, but were they already in decline and headed for inevitable collapse? For decades, this has been one of the great scientific debates.
Until now, most of the research on the extinction of the dinosaurs has been based on the fossil records of the Hell Creek formation, an enclave spread between the states of Montana, the Dakotas and Wyoming, in the United States, but none has clarified whether the sudden extinction of these vertebrates at the end of the Cretaceous was taking place before the cataclysm.
Today, a new study, based on new geochronological data collected in the rock formation of Ojo Álamo (New Mexico) – an area rich in fossils from between 66.4 and 66 million years ago, that is, contemporary with those of the American sites – concludes that the dinosaurs that populated North America 400,000 years before the asteroid impact were “very diverse and varied” and were, therefore, very far away. of the collapse.
Details of the study, carried out by an international team led by Andrew G. Flynn, a researcher at New Mexico State University, Baylor University, and the Smithsonian Institute in the United States, have been published in the journal Science.
Dating methods
Using radioisotope dating and magnetostratigraphy dating, the authors fixed the geological age of the Naashoibito Member of the Ojo Álamo formation at around 350,000 years before the extinction.
“Unlike the Hell Creek area, which has classic dinosaurs such as Triceratops, Tyrannosaurus rex or Edmontosaurus, this area was dominated by Alamosaurus, the only large long-necked sauropod left in North America at the end of the Cretaceous,” explains Jorge García-Girón, researcher at the University of León and co-author of the research, to EFE.
When comparing this fauna with what was in the southern area of New Mexico, the authors found that at the end of the Cretaceous there were “very notable differences” between both areas, both in forms of diversity, as well as in size, species richness, adaptation or diet, evidence of a “very high heterogeneity” between the dinosaurs of the north and the south that prove that they did not show signs of ecological decline before extinction massive.
Quite the contrary, “we have found sustained empirical evidence that there was a high degree of provinciality in these animals”, that is, that there were great differences between the northernmost and southernmost fauna, and that “allows us to affirm that there was no taxonomic decline” in the ecosystems and “close a decades-long debate” in paleontology.
The study also points out that the evidence found on other continents – although less precise in terms of dating – also suggests that in the rest of the planet there were “equally robust and diverse” dinosaur faunas and that they survived until the last moments of the Cretaceous.
However, to demonstrate it empirically “it is necessary to have a better biochronological record of the fossils from the end of the Cretaceous in other parts of the world and to have dating as precise as the ones we have done in this study to have a small time window that allows us to ‘zoom in’ within the geological record and have a few hundred thousand years over which to do the analysis,” the researcher specifies.
Meanwhile, “nothing suggests” that the diversity of dinosaurs was very different on other continents before they were abruptly exterminated by the asteroid impact, he concludes.
A perspective
In an accompanying perspective, Lindsay Zanno of North Carolina State University explains that clarifying whether dinosaurs were in decline before the meteorite impact is “highly relevant to humanity” because biodiversity on Earth is declining “at an alarming rate,” and studies suggest that impoverished ecological networks are more likely to collapse.
To predict the future of ecosystems, it is necessary to have an “empirical understanding” of the Earth’s fossil record, warns Zanno.
But almost all the fossil records from this time come from the formation of Hell Creek, whose biodiversity patterns have served to draw conclusions on a global scale although, obviously, the site does not include all species or contains species without an essential context such as precise estimates of geological age.
The latter is what the Naashoibito area in New Mexico provides – the expert emphasizes -, a new radioisotopic dating of the layers that demonstrates that the specific extinct species of southern North America were contemporary with the iconic faunas of Hell Creek.
Their results demonstrate that dinosaurs were divided into ecologically distinct northern and southern biomes during the last 10 million years of the Cretaceous, demonstrating that “hypotheses about the decline of dinosaurs before the asteroid impact underestimated their true taxonomic and ecological richness,” he concludes.
With information from EFE.
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