Earth’s ‘Great Dying’ killed 80-90% of life. How some amphibians survived.

When discussing mass extinction events, the asteroid impact that led to the extinction of the dinosaurs 66 million years ago is often the first to come to mind. However, the Permian-Triassic extinction event, also known as the Great Dying, was actually the most devastating loss of life in the planet’s history. Approximately 80 to 90 percent of all species on Earth were wiped out during this period of drastic climate change around 252 million years ago, completely altering the planet’s biosphere.

Despite the widespread devastation, some species managed to survive, including a group of primitive amphibians known as the temnospondyls. These amphibians may have survived the Great Dying by feeding on freshwater prey that larger land-based predators couldn’t access and by being adaptable eaters. These new findings were detailed in a study published on March 4 in the journal Royal Society Open Science.

Around 250 million years ago in the Early Triassic period, continuous volcanic activity resulted in global warming, arid conditions, decreased oxygen levels in the atmosphere, mega El Niños, acid rain, and wildfires. The landscape became so harsh that the tropics became devoid of animal life. This tropical dead zone had significant impacts on the distribution of both marine and terrestrial organisms on Earth. Despite this, some organisms like sharks, horseshoe crabs, and temnospondyls managed to survive.

Aamir Mehmood, an evolutionary biologist at the University of Bristol in the United Kingdom and a co-author of the study, stated, “One of the great mysteries has been the survival and flourishing of a major group of amphibians called the temnospondyls.” He further added, “These were predatory animals that fed on fishes and other prey but were primarily linked to the water, similar to modern amphibians like frogs and salamanders. We know that climates were hot back then, especially after the extinction event. How could these water-loving animals have been so successful?”

To unravel this mystery, Mehmood and the research team collected fossil data from 100 temnospondyls that lived during the Triassic period. They analyzed how their ecologies changed by examining parts of their skulls, teeth, and body sizes to understand their specific functions.

Surprisingly, the study found that the temnospondyls did not undergo significant changes during the crisis. They maintained the same range of body sizes as they did in the earlier Permian period. Some temnospondyls were small and fed on insects, while others were larger and had different feeding habits. The larger temnospondyls played a crucial role in their survival.

Armin Elsler, a paleontologist and co-author of the study, explained, “These larger forms included long-snouted animals that trapped fishes and broad-snouted generalist feeders. What was remarkable was how their diversity of body sizes and functional variety expanded about 5 million years after the crisis and then declined.”

During the initial five million years of the Triassic period marked by intense global warming, both terrestrial and marine organisms migrated away from the tropics to escape the extreme heat. The temnospondyls, however, managed to traverse the tropical dead zone, showcasing their resilience.

The study suggests that the key to their success lay in their generalist feeding ecology. Temnospondyls could adapt to feeding on various prey types, despite the environmental changes. Their ability to thrive in sparse water bodies and consume diverse prey contributed to their survival.

However, this success was short-lived, as the temnospondyls began declining in the Middle Triassic period with the emergence of mammal and dinosaur ancestors.

Mehmood noted, “Their burst of success in the Early Triassic was not sustained.” Eventually, temnospondyls went extinct around 120 million years ago. While they have no living descendants, some evolutionary biologists view them as a crucial step in the evolution of today’s diverse amphibians. Studying these ancient periods can provide insights into how modern amphibians like frogs, salamanders, and toads might cope with present environmental challenges, as amphibians are among the most endangered animal groups due to diseases and climate change.