Paleontologists have collected and examined over 1,000 dinosaur eggshell samples from a fossil-rich site in the Shanyang Basin of central China — one of the most abundant dinosaur records from the Late Cretaceous epoch. The researchers have found only three eggshell types representing two dinosaur groups — oviraptors and hadrosaurs — in sediments deposited between 68 and 66 million years ago, indicating sustained low dinosaur biodiversity. They suggest that the end-Cretaceous catastrophic events, such as the Chixulub impact and the Deccan Traps volcanism, probably acted on an already vulnerable ecosystem and led to the extinction of non-avian dinosaurs.
An artist’s depiction of a Late Cretaceous oviraptorosaur, a hadrosaur, and a tyrannosaur in central China. Image credit: Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences.
The demise of non-avian dinosaurs at the end of the Cretaceous period is a large component of one of the most severe mass extinctions of the Phanerozoic Eon.
The impact of an asteroid roughly 10 km in diameter in the Yucatán Peninsula, Mexico, and the resulting environmental destruction is a widely accepted causal mechanism for dinosaur extinction.
Despite that consensus, there are extensive ongoing disagreements about whether the dinosaur extinction was geologically abrupt, coinciding with the impact, or more gradual, occurring over millions of years.
“By examining the dinosaur record in China, we hoped to determine whether this declining trend extended to Asia as well,” said Dr. Qiang Wang from the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences and colleagues.
In their study, the authors systematically collected more than 1,000 well-preserved dinosaur eggshells and several complete and incomplete dinosaur eggs from 44 levels of sediments in the Shanyang Basin, China.
“We obtained detailed age estimates of the rock layers by analyzing and applying computer modeling to over 5,500 geological samples,” they said.
“We were able to create a timeline of nearly two million years at the end of the Cretaceous — with a resolution of 100,000 years — representing the period right before the mass extinction.”
“The fossils collected from the Shanyang Basin represented only three different dinosaurian eggshell species (oospecies): Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis.”
“In addition, two of the three dinosaur oospecies were from a group of toothless dinosaurs known as oviraptors, while the other is from the plant-eating hadrosaurid group.”
“A few additional dinosaur bones from the region show that tyrannosaur and sauropod also lived in the area between about 66.4 and 68.2 million years ago.”
“This low diversity of dinosaur species was sustained in central China for two million years before the mass extinction.”
“Our results suggest that dinosaurs were probably declining globally before their extinction.”
The findings were published in the Proceedings of the National Academy of Sciences.
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Fei Han et al. 2022. Low dinosaur biodiversity in central China 2 million years prior to the end-Cretaceous mass extinction. PNAS 119 (39): e2211234119; doi: 10.1073/pnas.2211234119
Source link: https://www.sci.news/paleontology/cretaceous-dinosaur-biodiversity-11228.html
