Look back enough in time and a pattern can emerge. After studying thousands of ancient fossils, paleontologist Jack Sepkoski identified such a thing in 1981: an epic sequence of life and death, engraved on 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 faunas of marine animals: a trio of successive explosions of biodiversity in the ocean along the Phanerozoic Aeon.
These giant blooms of marine life added to catastrophes of scale that changed the world: extinction-level events that precipitate the mass death of animals, while clearing the stage for new creatures to appear and thrive in spaces that go leave behind.
But it doesn’t have to happen that way, a new study suggests. Equally powerful forces, capable of shaping macroevolutionary processes with planetary implications, do not always require asteroids or supervolcanoes.
Sometimes the fire comes from within.
“The fossil record tells us that some of the key transitions in life history were rapid changes caused by abrupt external factors,” explains paleontologist Michal Kowalewski of the University of Florida.
“But this study shows that some of these important transitions were more gradual and may have been driven by biological interactions between organisms.”
The case at this point is what is known as the Marine Mesozoic Revolution. Beginning about 150-200 million years ago, this transition represents all the macroevolutionary changes that occurred as marine predators such as bony fish, crustaceans, and predatory snails increased, forcing their invertebrate prey. , such as mollusks, to adapt defenses against shell crushing attacks.
In the new research, which used modeling to demonstrate the network of relationships between giant sets of prehistoric marine life forms, the team found that the Mesozoic Marine Revolution effectively represents a fourth unrecognized chapter in growing biodiversity within the Phanerozoic. , equal in its power three great evolutionary faunas that Sepkoski identified decades ago.
“We are integrating the two hypotheses: the Mesozoic Marine Revolution and the three great evolutionary faunas into a single story,” explains first author and paleontologist Alexis Rojas of Umeå University in Sweden.
“Instead of three phases of life, the model shows four.”
Ultimately, although the Mesozoic Marine Revolution was characterized by gradual ecological changes produced by marine interactions over millions of years, researchers say it nevertheless triggered a prolonged biotic transition comparable in magnitude to the transition. end of the Permian.
This episode, often called the Great Dying, occurred about 250 million years ago and was the most severe mass extinction event on Earth, killing approximately 80% of all marine species (and 70% of terrestrial vertebrates).
Then life rebounded with the third great evolutionary fauna, known as the modern fauna period, according to Sepkoski’s framework.
But according to Rojas, Kowalewski and his team, the modern period intersected with the Mesozoic Marine Revolution, contributing to a recognizable transition in biodiversity in the Earth’s marine life during the Middle Cretaceous period, about 129 million years ago. .
“What we’ve really built is an abstract fossil record that provides a unique perspective on the organization of marine life,” Rojas says.
“At the most basic levels, this map shows ocean regions with specific animals,” he adds. “The basic components of our study are the animals themselves.”
The findings are reported in Biology of Communications.