Scientists have discovered that shallow, lagoon-like environments were the cradle for vertebrate evolution, giving rise to our distant ancestors.
A study led by palaeobiologist Lauren Sallan from the University of Pennsylvania, US, and [published] in the journal Science, solves one more piece in the long-standing puzzle of the evolutionary origin of vertebrates.
The very first vertebrates – fish – are thought to have evolved in the mid-Palaeozoic era around 480 million years ago, but the fossil record from this time contains only elusive fragments of these ancestral species. By 420 million years ago, the record shows a huge proliferation of fish – so what happened in the intervening 60 million?
The study by Sallan and colleagues analyses the entire early environmental record of primitive fish – comprising 2728 previously published records – to create a huge new dataset. This allowed them to reconstruct these ancestral habitats, using mathematical models to fill in the gaps.
“Our work shows that almost every major vertebrate division, from the earliest armoured jawless fish all the way up through sharks and our own ancestors, all started out right near the beach, far inshore of the reef,” Sallan says.
These fragile near-shore environments – either intertidal areas or permanently shallow lagoons – explain why so few early fish fossils are found intact: waves likely blasted them into tiny fragments.
Importantly, the study also shows that these restricted areas remained cradles of diversification for a long time.
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