Chinese dinosaurs declined two million years before extinction

(ORDO NEWS) — Chinese geologists and paleontologists have examined dinosaur eggshell fossils from the Shanyang Basin in Central China and concluded that the dinosaurs in the region experienced a two-million-year decline before becoming extinct. This study supports the view that the asteroid impact only hastened the extinction of the dinosaurs.

The Cretaceous-Paleogene extinction event, which occurred 66 million years ago, affected many groups of animals, but became widely known mainly due to the extinction of non-avian dinosaurs.

At present, the impact hypothesis of extinction prevails among scientists: the biospheric crisis was caused by the fall of an asteroid with a diameter of about ten kilometers (but there is an alternative point of view, according to which the extinction was caused by volcanism on the Indian plate).

However, paleontologists disagree on the details of the extinction of dinosaurs: some experts believe that their extinction was sudden (1, 2, 3), others that this group was already in decline and the impact event simply accelerated their extinction (4, 5, 6). The dispute is complicated by

Fei Han of the China University of Geosciences and his colleagues studied in detail the state of the Late Cretaceous dinosaur fauna in Central China. Using magnetostratigraphy, cyclostratigraphy, and biostratigraphy, researchers have dated rocks from the Shanyang Basin in East Qinling to within 100,000 years.

It turned out that the basin contains continuous deposits ranging in age from 71.7 to 64.6 million years, that is, it covers the end of the Cretaceous and the beginning of the Paleogene.

At the same time, fossil eggshells and whole dinosaur eggs found here come from deposits ranging in age from 68.2 to 66.4 million years (in addition, bones of hadrosaurids, sauropods and theropods, including an unknown tyrannosaurid, were also found in these deposits).

Chinese dinosaurs declined two million years before extinction 2
Fossil egg of Macroolithus yaotunensis

Scientists have analyzed more than 1,000 fossil dinosaur shells and eggs and determined that they belong to just three ootaxa: Macroolithus yaotunensis, Elongatoolithus elongatus and Stromatoolithus pinglingensis.

The first two ootaxa belong to the Elongatoolithidae and most likely belong to small theropod oviraptorosaurs, while S. pinglingensis is attributed to hadrosaurids. According to previous work, the diversity of ootaxa and dinosaur taxa is higher in earlier deposits of other East Qinling basins.

The results of scientists speak of a low level of diversity of dinosaurs in this region for almost two million years before the extinction. Researchers tentatively attribute this decline to climatic changes at the end of the Cretaceous.

Chinese dinosaurs declined two million years before extinction 3
Dinosaur fossils and fossil eggs from the East Qinling Basins (B) on the geochronological scale (A) and the global distribution of Upper Cretaceous dinosaur localities (C). Taxa and ootaxa from the Shanyang Basin shown in black

According to the authors, in order to finally resolve the dispute about the extinction of dinosaurs, it is necessary to increase the sample of taxa, its spatiotemporal coverage, and also use high-precision dating of fossils. Fei Han and his co-authors believe that their study is an important step in this direction.


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