About 445 million years ago, Earth underwent a dramatic shift, with a massive extinction event fundamentally reshaping marine life. The Late Ordovician mass extinction (LOME) wiped out roughly 85% of ocean species, triggered by glacial expansion and drastic climate change. However, this upheaval wasn’t just destruction; it created an opportunity for one group to rise: jawed vertebrates. A new study published in Science Advances confirms that this extinction directly propelled the dominance of jawed fishes, setting the evolutionary trajectory for all vertebrates, including humans, that followed.
The Ordovician World Before the Catastrophe
Before the LOME, the planet was dominated by the supercontinent Gondwana, surrounded by warm, shallow seas. There were no polar ice caps, and life flourished in the oceans. Creatures like large-eyed conodonts, tiny trilobites, and even sea scorpions the size of humans thrived. Among them were the ancestors of gnathostomes – jawed vertebrates. But this world was about to change drastically.
The Double-Wave Extinction
The extinction unfolded in two phases. First, the climate shifted rapidly from warm to frigid as Gondwana froze over, drying out shallow habitats. Then, millions of years later, the ice melted, and surviving species drowned in warm, oxygen-depleted water. Most vertebrates retreated into isolated refugia – biodiversity hotspots shielded by deep oceans. It was within these zones that jawed vertebrates gained a crucial advantage.
The Rise of Jaws: A Database of Survival
Researchers compiled years of paleontological data to reconstruct ecosystems during this period. The analysis showed a clear link between the mass extinction and a subsequent surge in jawed vertebrate diversity. These survivors were concentrated in stable refugia, such as what is now South China, where early shark-like fossils appeared. Over millions of years, they evolved the ability to colonize other ecosystems.
Opportunity in Ecological Vacancy
The study suggests that jaws didn’t evolve to fill a new niche; rather, jawed vertebrates filled niches left open by extinct jawless species and arthropods. Confined to small areas with abundant vacancies, they diversified rapidly. This is analogous to Darwin’s finches on the Galápagos Islands, which adapted their beaks to exploit new food sources.
The Diversity Reset Cycle
The LOME didn’t wipe the slate clean; it reset the ecological structure. Early vertebrates stepped into roles previously occupied by conodonts and trilobites, rebuilding ecosystems with new players. This “diversity-reset cycle” repeats after other extinction events, with evolution converging on similar designs. The study confirms that the dominance of jawed vertebrates wasn’t just chance—it was a direct outcome of the LOME.
Ultimately, this research sheds light on why jaws evolved, why jawed vertebrates prevailed, and why modern marine life traces back to these survivors. By revealing these long-term patterns, evolutionary biology gains deeper insight into the forces that have shaped life on Earth.
