A Child's Discovery Could Rewrite Millions Of Years Of Marine Evolution

Fossil shallow-water Southern Hemisphere isocrinid crinoids that survived up to 30 million years after they were confined to deep water in the Northern Hemisphere. Whittle et al/Communications Biology

When Professor Ken McNamara's children were small he took them fossil hunting. On one trip, McNamara's then-4-year-old daughter turned up something he said; “wasn't supposed to be there”. It's taken almost 30 years, but her find has led to a paper overturning much of what we thought we knew about isocrinid crinoids, also known as sea lilies, once a dominant feature of the marine ecosystem.

For something like 500 million years, crinoids dominated shallow-water marine ecosystems. However, around the time the dinosaurs reigned on land, an increasing variety of marine predators entered their habitat. The crinoids are echinoderms along with sea stars and sea urchins, and have stalks rather than being free-floating. They're filter-feeders with little protection (unlike sea urchins) and largely disappeared from shallow waters around the time the dinosaurs lost their dominance. Their retreat to more lightly predated depths is part of the Marine Mesozoic Revolution

At least we thought so until McNamara, a Cambridge University palaeontologist, took his children on a field trip to an Albany quarry on Western Australia's south coast. “Children are great,” he told IFLScience. “They're free labor, have great eyesight and they're close to the ground.” Whatever child labor laws might say about such things, it worked, as McNamara's daughter turned up a fossil crinoid from an apparently shallow-water site tens of millions of years after these were thought to have been abandoned.

The discovery led to a wider search, involving the identification of hundreds of sea lily fossils near Exmouth in north-west Western Australia that indicate crinoids were flourishing in shallow Australian waters 33 million years later. In conjunction with Dr Rowan Whittle of the British Antarctic Survey, McNamara has now published a paper in Communications Biology revealing the crinoids survived in shallow waters for tens of millions of years across much of the Southern Hemisphere after their big retreat in the north, making this a much more significant matter than a local anomaly. McNamara's daughter doesn't get authorial credit, but he assures us a species will be named after her in a forthcoming paper.

Northern Western Australia appears to have been particularly important to shallow water sea lilies' survival, with species spreading from there on ocean currents. McNamara even thinks crinoid dispersal can track the history of Southern Hemisphere currents.

Locations of sites where shallow-water sea lily fossils have been found after they disappeared from the Northern Hemisphere, and major ocean currents. Whittle et al/British Antarctic Survey

McNamara admitted to IFLScience the reason the timescales between the hemispheres are so different remains unclear. “We thought it might be an absence of the predators, but we found sea urchins in some of the same deposits,” he said. Whatever the explanation, the sea lily story is, he said, “more complex than we first thought, and that makes it more interesting.”

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