Fossil Shows That Dinosaurs Were Declining Before the Asteroid Hit

Courtesy of Mike Shaver (Flickr CC0)

Around 65 million years ago, a huge asteroid struck the earth and contributed to the worldwide extinction of dinosaurs, leaving birds as their one living relative. Scientists believe that a wide selection of dinosaurs lived all through the world at the end of the Cretaceous period, right before their extinction. Although scientists have argued whether or not dinosaurs were at their peak prior to extinction or already in decline before their death. In simpler terms, how did dinosaurs go out, did they go out with a bang or a whimper?

Researchers from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, along with their collaborators, have figured out the answer. They have found evidence supporting the idea that dinosaurs were not different prior to their extinction, and in fact declined overall during the last part of the Cretaceous.

North America provides the majority of the scientific information about the demise of the dinosaurs. While some published studies contend that the dinosaur populations were prospering before their mass extinction, other extensive research projects prove that the dinosaurs were truly in decline, which prepared them for the following events of their inevitable mass extinction.

The Chinese researchers sought to discover whether this falling tendency persisted throughout Asia by looking at the dinosaur record in China.

Courtesy of Cherrysweetdeal (Flickr CC0)

Over 1,000 fossilized dinosaur eggs, along with shell pieces, coming from the Shanyang Basin in China, were analyzed by the researchers. These fossils were found in rock layers that were about 150 meters thick overall.

Through the examination of more than 5,500 geological samples and the use of computer modeling, the researchers were able to determine the precise ages of the rock layers. As a result, the researchers were able to construct a timeline at the end of the Cretaceous that covered about 2 million years and had a resolution of 100,000 years, marking the time just prior to extinction. Comparisons with worldwide data are available using this timeline.

Based on the data from the Shanyang Basin, the scientists found a drop in the diversity of dinosaur species. For instance, just three different species of dinosaurs, Macroolithus yaotunensis, Elongatoolithus elongatus, and Stromatoolithus pinglingensis, are represented amidst the 1,000 dinosaur egg fossils that were discovered in the basin. In addition, two out of three dinosaur eggs are owned by a group of toothless dinosaurs, and oviraptors, and the third is from the hadrosaurid group, which consumed plants also known as duck-billed dinosaurs.

Tyrannosaurus and sauropod dinosaurs also lived in the area between approximately about 66 and 68 million years ago, according to a few dinosaur bones that were found in the area. Prior to the mass extinction, central China had low diversity of dinosaur species throughout the previous 2 million years. Shanyang Basin and central China contain a sparse dinosaur population and are nowhere compared to the setting of Jurassic Park.

Together with data from North America, these findings imply that dinosaur populations were likely falling globally before their extinction.

The sustained low number of dinosaur lineages for the last few million years and the long-term worldwide decline in their diversity through the end of the Cretaceous Period may have been brought on by known global climate fluctuations and large volcanic eruptions, specifically the Deccan Traps in India. These factors might’ve caused ecosystem-wide instability, leaving dinosaurs that were not birds vulnerable to a mass extinction that happened at the same time as the asteroid impact.

Written By Lance Santoyo


PHYS: Chinese fossil eggs show dinosaur decline before extinction

Forbes: Fossil Eggs Show Dinosaur Decline Before End-Cretaceous Extinction

The Week: Dinosaurs ‘already declining’ when asteroid hit

Featured Image Courtesy of Mike Shaver Flickr Page – Creative Commons License

Inset Image Courtesy of Cherrysweetdeal Flickr Page – Creative Commons License

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