New Zealand's fossil record offers clue to predicting marine extinctions
Scientists are using New Zealand's unique marine fossil record to identify which molluscs and invertebrates face the highest extinction risk before species disappear for good.
Humanity may be triggering a sixth mass extinction — the first caused entirely by human activity. Unlike the five previous extinction events, which were driven by dramatic natural upheavals such as asteroid impacts, today's accelerating extinctions threaten to reshape ocean ecosystems in ways we're only beginning to understand.
The challenge is that extinction remains unpredictable until it's too late. The passenger pigeon, once likely the most abundant bird on Earth, vanished within decades in the 19th century — a collapse no one foresaw. Predicting which species will follow is harder still, especially for the vast, hidden world of marine invertebrates that sustain ocean food webs.
Where fossils reveal future risk
New Zealand holds a unique advantage: its fossil record of marine molluscs — clams, snails and related species that have lived in its waters for millions of years. By studying which marine invertebrates proved vulnerable to extinction in the geological past, scientists can identify which living species face similar risks today.
"Using fossils, we can identify which particular subsets of marine invertebrates have been most vulnerable to extinction in the past and, therefore, might be at particular risk of future extinction," according to research published in The Conversation. In this way, researchers need not wait for extinction to occur to sound the alarm.
The extinction debt
This approach allows scientists to quantify what they call an "extinction debt" — a measure of how many species are already committed to future extinction because of human actions underway today. By understanding this debt now, conservationists can intervene before it becomes irreversible.
Most species facing extinction are never listed on the International Union for Conservation of Nature's red list.
The bias in conservation tracking is stark. Birds and mammals dominate the IUCN red list because only a tiny fraction of invertebrates, particularly ocean-dwelling species, have been formally evaluated against conservation criteria. This means the true scope of biodiversity loss remains largely invisible.
Why it matters
The loss of marine invertebrates threatens the fundamental systems that sustain life on Earth — the intricate web of physical, chemical and biological processes that keep the planet habitable. Yet because most ocean invertebrates are small, difficult to study and live out of sight, their plight goes largely unnoticed until whole ecosystems begin to fail.
Species that are easy to protect — like the New Zealand kākāpō, a flightless night parrot, or the blue whale — draw resources and attention. But the countless molluscs, crustaceans and other invertebrates that hold ecosystems together rarely make headlines, even as their numbers fall.
The fossil laboratory
New Zealand's geological record provides what researchers call "natural experiments" — a window into which marine species have survived environmental upheaval in the past and which have not. Fossil beds like the 18-million-year-old shell deposits found in White Rock River, Canterbury, contain the remnants of species that either thrived, adapted or disappeared as the world around them changed.
By mapping these patterns, scientists can predict vulnerability without waiting for extinction to confirm it. This fossil-informed approach offers a tool to slow accelerating extinction rates — but only if it prompts action before the extinction debt becomes payable.