At the end of the Permian period some 252 million years ago, global climate change killed off 95 percent of the planet’s species. Now, researchers studying carbon isotopes and ocean chemistry confirm that marine reptiles recovered rapidly after that mass extinction event: They invaded the oceans within just 3.35 million years. The findings are published in Scientific Reports this week.
A new, 248-million-year-old marine reptile called Sclerocormus parviceps was described in a study published last month. This toothless ichthyosauriform from the Early Triassic had an extremely small head and a long, fluke-less tail. The new species was described as “aberrant” with a “hitherto unknown body design.” The discovery suggested that the extent of marine reptile diversity has yet to be fully uncovered and that life evolved quickly after the Great Dying. Until recently, the recovery was thought to be slow and delayed.
However, the timing of marine ecosystem recovery following the end-Permian mass extinction remains poorly constrained. So, an international team led by Peking University’s Da-yong Jiang and Isabel Montañez of UC Davis turned to carbon cycling and ocean chemistry. Carbon cycles are paced by obliquity (Earth’s tilt) and eccentricity (how circular or elliptical Earth’s orbit is). These shift over time, and their cycles help researchers better understand climate and biosphere dynamics of the past. The team examined carbonate samples collected from the Majiashan section of Chaohu in southern China.
During or just after the end-Permian mass extinction event, the process of vertical mixing in the oceans stopped. These large-scale movements help circulate nutrients and oxygen, and they depend largely on temperature. Global warming at the end of the Permian – likely caused by the release of carbon dioxide from massive volcanic eruptions – led to the depletion of oxygen throughout the world’s oceans.
The team discovered that the first appearance of marine reptiles 248.81 million years ago occurred at the same time the oceans regained their healthy circulation. That means the restoration of deep ocean ventilation helped facilitate complex ecosystems and the reptile invasion into the sea. “We attribute the biotic recovery and initiation of a new marine ecosystem to the final breakdown of this ocean stratification and the return to an oxygenated ocean,” Montañez said in a statement. It took 3.35 million years for the marine ecosystem to recover.