The age of fishes began after a wave of mass death, fossil database shows

How Ancient Mass Extinction Cleared the Way for the Age of Fishes (Images: Canva)

A study published in Science Advances shows the Late Ordovician Mass Extinction, which wiped out about 85 percent of marine species, created conditions that allowed jawed vertebrates to diversify and eventually dominate marine ecosystems, reshaping the course of vertebrate evolution.

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Scientists have uncovered how a catastrophic ice age extinction reshaped early marine life, revealing that the dominance of jawed vertebrates emerged directly from environmental collapse nearly 445 million years ago.

Researchers from the Okinawa Institute of Science and Technology reported findings in Science Advances. The study focused on the Late Ordovician Mass Extinction event. This extinction eliminated roughly 85 percent of marine species. Glaciers spread across Gondwana, draining shallow seas rapidly. Ocean chemistry shifted dramatically during this climatic upheaval. Life on Earth changed within a geological moment. Scientists now link this disaster to vertebrate evolutionary success.

Late Ordovician extinction and environmental collapse

The Ordovician period spanned between 486 and 443 million years ago. Earth’s climate was warm before rapid glaciation began. Gondwana dominated southern latitudes and supported shallow seas. Early plants and arthropods colonised coastal environments. Oceans hosted diverse creatures including trilobites and giant predators. Jawed vertebrate ancestors were rare and insignificant then. The extinction unfolded in two distinct destructive phases. First, cooling climates removed shallow marine habitats. Later warming flooded ecosystems with oxygen-poor waters. These shifts devastated marine biodiversity across regions.

Professor Lauren Sallan led the Macroevolution Unit research team. She said jawed fishes rose because extinction occurred. Fossil records show clear ecological shifts after LOME. Survivors clustered in isolated marine refugia. These refugia were separated by deep ocean barriers. Jawed vertebrates gained advantages within these stable environments.

Fossil records reveal refugia and diversification

First author Wahei Hagiwara compiled extensive fossil databases. The team analysed 200 years of paleontological records. Data covered Late Ordovician and Early Silurian periods. Researchers reconstructed ecosystems surviving within refugia zones. They measured genus-level diversity across time intervals. Results showed gradual but sustained gnathostome diversification. Increased speciation followed extinction pulses after millions of years.

Biogeography proved essential for understanding evolutionary pathways. Scientists tracked species movement across ancient oceans. South China emerged as a crucial evolutionary refuge. Fossils there include early jawed fish ancestors. Some resembled modern sharks in body structure. These fishes remained isolated for extended evolutionary periods. Eventually they adapted to cross open oceans.

Evolutionary meaning of jaws and future patterns

Researchers questioned whether jaws created new ecological niches. Evidence suggests niches existed before jaw evolution. Gnathostomes filled vacant roles left by extinct species. Jawless vertebrates continued evolving elsewhere simultaneously. They dominated wider seas for another 40 million years. Later jawed vertebrates spread globally and prevailed.

The study suggests extinctions reset ecosystems rather than erase them. New species rebuilt similar ecological structures repeatedly. Scientists describe this as a recurring diversity reset cycle. Similar patterns appear throughout the Paleozoic fossil record.

Professor Sallan said integrating fossils and geography clarified evolution. The work explains why jawed vertebrates dominate today. Modern marine life traces back to these resilient survivors.