Did the meteor hit the dinosaurs at their career high, or was it more of a bang at the end of a slow decline? A study now provides further evidence that the catastrophe struck around 66 million years ago in a dinosaur world already marked by species extinction. Using egg fossils, the paleontologists show that during the last chapter of the Cretaceous, there was also a decline in biodiversity in Asia. The low biodiversity could have contributed to the fact that, apart from the birds, no dinosaurs survived the caesura, say the researchers.
For many millions of years, they dominated the world's animal world and brought forth an enormous variety of species: The dinosaurs were downright successful models in the history of evolution. The end of the Cretaceous period was still clearly characterized by these highly developed beings. But then suddenly there was a shot: around 66 million years ago, a huge meteorite crashed into the earth in the area of today's Yucatan peninsula and caused a global catastrophe. Paleontologists largely agree that this sealed the age of the dinosaurs: all species except the ancestors of modern-day birds were swept off the stage of evolutionary history by the direct and indirect effects of the impact.
Did the blow come out of the blue?
However, there has been a controversy for some time as to what state the dinosaur world was in at the time of the apocalypse. Some research suggests that this group of animals experienced a career peak at the end of the Cretaceous. But since then there have been increasing indications that the meteorite impact had caught them on a rather weak foot. Most recently, a study on the development of dinosaur biodiversity in present-day North America revealed a decline in biodiversity in the run-up to the meteorite impact. But it could also have been a more regional phenomenon and not a global trend, one objected.
As part of their study, the scientists led by Fei Han from the China University of Geosciences in Wuhan wanted to find out to what extent finds from Asia also show a declining trend in dinosaur biodiversity in the Maastrichtian era. Their findings are largely based on examining fossil eggs found in the Shanyang Basin in central China. They come from a layered rock formation with a total thickness of about 150 meters. The special feature of the study lies in the comparatively precise dating of the deposits, the researchers emphasize: By analyzing more than 5,500 geological samples, they were able to identify finds from around two million years before the end of the Cretaceous period. Around 1,000 of these egg fossils were then assigned to dinosaur species based on their characteristics.
decline in biodiversity
As the team reports, there was a strikingly low level of biodiversity in the era of the last chapter of the Cretaceous: In the deposits from around 68 to 66 million years ago, the researchers found eggs from three different dinosaur species, which in turn can only be assigned to two groups are: the oviraptors and the hadrosaurs, also known as duck-billed dinosaurs. There is also information from other sites, according to which representatives of the tyrannosaur and sauropod family lived in the Maastrichtian era. From the previous period - the so-called Campanian - representatives of eight dinosaur groups are known from the East Qinling region, the scientists report.
Han and his colleagues conclude that the results also show a significant decline in dinosaur species in Asia at the end of the Cretaceous period. In conjunction with the earlier study results from North America, this finding supports the assumption that this animal group was on the decline even before its extinction. The scientists explain that this could have been due to known global climate fluctuations and volcanic eruptions at the end of the Cretaceous period.
According to them, many specialists may have fallen victim to the instability of the ecosystems. More adaptable representatives may also have coped with the adverse Maastrichtian conditions, as they may have been able to use a wide range of food plants. Ultimately, however, they too were apparently unable to cope with the extreme consequences of the meteorite impact. Fewer species probably meant less basic potential for survivors: The low biodiversity could have contributed to the fact that no dinosaur species survived the catastrophic time, the researchers say, apart from the ancestors of birds.
Source: Chinese Academy of Sciences, professional article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2211234119