One of the most widespread theories regarding the extinction of dinosaurs is that, when the asteroid Chicxulub crashed into Earth causing a climate catastrophe that wiped out 75% of all living species, lizards were already in decline, and therefore more vulnerable to extinction itself.
A study published in Sciencehowever, now casts doubt on this idea, suggesting instead that, at the time of the asteroid’s fall, the dinosaurs were doing very well, in terms of quantity and also variety of species.
On the eve of extinction. The study was conducted on dinosaur populations that inhabited what is now New Mexico, particularly those of the so-called Kirtland Formation. These are fossils that date back to a period between 66.4 and 66 million years ago, therefore exactly at the turn of the extinction event caused by the asteroid (and by a series of other contributing causes, but let’s get over the simplification). The team was therefore able to analyze in detail the health status of dinosaurs that experienced extinction in an area relatively close to where Chicxulub impacted the planet.
Killer asteroid. The results of the analysis say something very simple and very clear: other than declining, before the asteroid the dinosaurs were doing very well. Both from a quantitative point of view (the populations of New Mexico are very numerous) and from a biodiversity point of view: all of North America was populated by dinosaurs, who lived in distinct communities separated from each other by climatic factors. In particular, the so-called “bioprovinces” into which North America was divided were characterized by different climates (and therefore temperatures).
Damn asteroid! To summarize: on the eve of extinction, New Mexico (and all of North America in general) was teeming with dinosaurs, who occupied all available environments, choosing them according to their needs. Confirmation of how favorable the ecosystem was to dinosaurs comes from what happened after their extinction: within 300,000 years, mammals diversified and took their place, however distributing themselves according to the same division into bioprovinces that characterized the dinosaurs.
Catastrophe. In short, the climate continued to guide the evolution of life in North America even after the disappearance of the dinosaurs, and according to the same rules. The study therefore demonstrates that dinosaurs were not already “launched” towards extinction when Chicxulub fell: their disappearance was sudden and unexpected, caused by an unpredictable catastrophe. In short: who knows how things would have gone without that asteroid…
