Reptiles quickly invaded the seas shortly after a global extinction, according to researchers at the University of California, Davis.
The likely global climate change caused by massive volcanic eruptions destroyed 95 percent of all species 250 million years ago, at the end of the Permian period. But terrestrial reptiles colonized the ocean in just 3.35 million years at the beginning of the Triassic, a rapid recovery in geological time, according to the study published in Scientific Reports.
A chinese researcher called Fu, focused on the analysis of fossils and rock samples obtained at the site of Majiashan in Chaohu, southern China.
The oldest fossils of marine reptiles were 248.81 million years ago, according to the study. These marine reptiles including ichthyosaurs pioneers and sauropterygians, like dolphins, came to dominate the Mesozoic seas during the age of dinosaurs animals.
At the same time, there were major changes in ocean chemistry and the carbon cycle, according to the researchers. Vertical mixing of ocean waters had stopped during or shortly after the mass extinction, causing widespread depletion of oxygen in the oceans. Carbon isotopes in the rock layers of Majiashan suggest that the oldest marine reptiles appeared after the return of healthy ocean circulation, which may have induced ecosystem recovery, according to a University. The rocks showed a more vigorous mixing of ocean waters with nutrient-rich waters surface that fed small organisms at the bottom of the ocean food chain.
“We attribute the biotic recovery and the start of a new marine ecosystem to the final breakdown of the stratification of the ocean and return to an oxygenated ocean,” said Isabel Montañez, coauthor of the study.
Carbon isotopes varied in the time scale of 405,000 years, 100,000 years, reports the study. These carbon cycles corresponds to the orbital eccentricity of the Earth, which alternates between more circular and more elliptical. These orbital variations provided means for dating the appearance of Mesozoic marine reptiles.
