Look far enough back in time and a pattern may appear. After studying thousands of ancient fossils, paleontologist Jack Sepkoski identified just that in 1981: an epic sequence of life and death, engraved in the skeletons of the last 500 million years.
The late Sepkoski, a professor at the University of Chicago, discovered what became known as the three great evolutionary fauna of marine animals – a trio of successive explosions of biodiversity in the ocean during the Phanerozoic Aeon.
These huge flourishes of marine life have been recorded by world-changing catastrophes: extinction events that precipitate the mass death of animals – simultaneously clearing the stage for new creatures to emerge and thrive in the spaces they have left behind. follow.
But that doesn’t have to be the case, a new study suggests. Equally powerful forces – capable of modeling macroevolutionary processes with planetary implications – do not always require asteroids or supervolcanoes.
Sometimes the fire comes from inside.
“The fossil record tells us that some of the key transitions in the history of life were rapid changes triggered by abrupt external factors,” says paleontologist Michal Kowalewski of the University of Florida.
But this study shows that some of these major transitions were more gradual and could have been driven by biological interactions between organisms.
The case at this point is what is known as the Marine Mesozoic Revolution. Since about 150-200 million years ago, this transition represents all the macroevolutionary changes that have taken place as marine predators, such as bony fish, crustaceans, and predatory snails, have forced their invertebrate prey, such as mollusks. , to adapt the defense against the boring and shell crushing attacks.
In the new research, which used modeling to demonstrate the network of relationships between gigantic sets of prehistoric marine life, the team found that the Mesozoic Marine Revolution was indeed a fourth, unrecognized chapter in increasing Phanerozoic biodiversity – equal in its power. with three large evolutionary faunas Sepkoski identified decades ago.
“We integrate the two hypotheses – the Mesozoic Marine Revolution and the three great evolutionary faunas into one story,” explains the first author and paleontologist Alexis Rojas of Umeå University in Sweden.
“Instead of three phases of life, the model shows four.”
Finally, although the Marine Mesozoic Revolution was characterized by gradual ecological changes produced by interactions with marine life over millions of years, researchers say it still triggered a prolonged biotic transition comparable in size to the final Permian transition.
This episode, often called the Great Dying, occurred about 250 million years ago and was the most severe mass extinction event on Earth, killing about 80% of all marine species (and 70% of terrestrial vertebrates).
After that, life returned with the third great evolutionary fauna, known as the modern fauna period, according to Sepkoski’s framework.
But according to Rojas, Kowalewski and their team, the modern period intersected with the Mesozoic Marine Revolution, contributing to a recognized transition of biodiversity into Earth’s marine life during the Middle Cretaceous period, about 129 million years ago.
“What we actually built is an abstract fossil record that offers a unique perspective on the organization of marine life,” says Rojas.
“At the most basic levels, this map shows the regions of the ocean with certain animals,” he adds. “The basic elements of our study are the individual animals themselves.”
The findings are reported in Biology of communications.