An underwater revolution millions of years ago rewrote the ocean script –

An underwater revolution millions of years ago rewrote the ocean script

If you look far enough back in time, a pattern may emerge. After studying thousands of ancient fossils, paleontologist Jack Sepkoski identified such a thing in 1981: an epic sequence of life and death, etched into skeletons for 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 bursts of biodiversity in the ocean throughout the Phanerozoic Eon.

These giant blooms of marine life were crowned by world-changing catastrophes of scale: extinction-level events that precipitated the mass death of animals, simultaneously clearing the stage for new creatures to emerge and thrive in the spaces they left 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 the history of life were rapid changes caused by abrupt external factors,” explains paleontologist Michal Kowalewski of the University of Florida.

“But this study shows that some of those 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 Mesozoic Marine Revolution. Beginning approximately 150-200 million years ago, this transition represents all of the macroevolutionary changes that took place as marine predators such as bony fish, crustaceans, and predatory snails increased in numbers, forcing their invertebrate prey, such as mollusks, to adapt defenses against crushing attacks piercing.

In the new research, which used models to demonstrate the web of relationships between giant assemblages of prehistoric marine life forms, the team found that the Mesozoic Marine Revolution effectively represents an unrecognized fourth chapter of growing biodiversity within the Phanerozoic, equal in power. to the three major evolutionary faunas that Sepkoski identified decades ago.

“We are integrating the two hypotheses: the Mesozoic Marine Revolution and the three great evolutionary faunas in a single story,” explains first author and paleontologist Alexis Rojas from 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 interactions of marine life over millions of years, the researchers say it triggered a protracted biotic transition comparable in magnitude to the final Permian transition.

This episode, often called the Great Dying, occurred approximately 250 million years ago and was the most serious mass extinction event on Earth, wiping out approximately 80 percent of all marine species (and 70 percent of all marine species). terrestrial vertebrates).

As a consequence, life recovered 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 recognizable transition in biodiversity in Earth’s marine life during the Middle Cretaceous period, about 129 million years ago.

“What we really build is an abstracted fossil record that provides a unique perspective on the organization of marine life,” says Rojas.

“At the most basic levels, this map shows ocean regions with particular animals,” he adds. “The building blocks of our study are the animals themselves.”

Findings are reported in Communications biology.


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