When the climate turned lethal and the oceans warmed, the animals that survived were often not the toughest or the most adaptable. They were the ones that could run — or more precisely, swim north or south to follow the temperature range their bodies needed.
A study published in Science has found that the shape and orientation of a coastline is one of the strongest predictors of extinction risk across the entire history of animal life. Animals trapped on east-west coastlines, inside inland seas, or on islands died at dramatically higher rates during every major extinction event of the last 540 million years. Animals on north-south coastlines — where migrating to a cooler or warmer latitude was simply a matter of swimming further along the coast — survived at far higher rates.
The researchers at the University of Oxford call these death zones “latitudinal traps.”
What They Did
The team, led by Dr Cooper Malanoski and Professor Erin Saupe, analysed more than 300,000 fossils from over 12,000 genera of marine invertebrates — shellfish, sea urchins, corals, and their relatives — spanning 540 million years of ocean life. They combined this fossil record with detailed reconstructions of where the continents were positioned at each point in time, then ran statistical models to test whether coastline orientation predicted which groups went extinct and which survived.
The signal was consistent across the entire fossil record. Animals living on east-west coastlines, or in enclosed inland seas, faced a reliably higher chance of extinction than animals living where they could move freely between latitudes.
The effect was strongest during the five great mass extinctions and during hyperthermal events — episodes when the Earth’s temperature spiked sharply.
Why This Matters
The mechanism is straightforward once you see it. Most marine animals have a preferred temperature range. When the climate shifts, animals need to move to stay within that range. On a north-south coastline — think the western coast of the Americas, or the eastern coast of Africa — moving toward a cooler or warmer zone simply means swimming up or down the coast. The habitat is continuous.
On an east-west coastline, it doesn’t work that way. Think of the Mediterranean Sea. An animal living on its northern shore cannot migrate south to escape warming because south is open ocean, not coastal habitat. It is trapped at its current latitude. When temperatures cross a threshold the animal cannot tolerate, there is nowhere to go. This is the latitudinal trap.
The same logic applies to animals living on isolated islands or inside enclosed inland seas. Warm water pours in. Cold water retreats. The animals that cannot move die.
This is not a subtle statistical effect. It held across every geological period, every major extinction event, and every major animal group the researchers examined.
The Modern Implication
This finding has a direct, unsettling application to the present day.
The Mediterranean Sea is an east-west body of water. So is the Gulf of Mexico. The Caribbean is dotted with islands. Large portions of Southeast Asia’s rich marine biodiversity sit in enclosed or semi-enclosed seas. According to the logic of this study, marine animals in these regions are structurally more vulnerable to extinction from anthropogenic climate change than animals living on open north-south coastlines.
The researchers are careful not to overclaim. The fossil record captures extinctions over millions of years; modern climate change is happening on a timescale of decades to centuries, and many other factors influence which species survive. But the underlying mechanism — that geographic imprisonment amplifies extinction risk when temperature shifts — operates regardless of how fast the temperature is changing.
What Changes
The conventional focus in extinction risk has been on biological traits: how fast a species reproduces, how specialised its diet is, how tolerant it is of temperature extremes. This study adds a variable that is entirely independent of what an animal is. It is a function of where the animal lives, and specifically whether the geography around it offers an escape route.
That has practical consequences for conservation. Marine protected areas are typically designated based on where biodiversity is richest today. This research suggests that geographic connectivity — the ability of a population to migrate between latitudes — deserves equal weight in that calculation.
The team’s next step is to test whether the latitudinal trap effect is already visible in modern data, as ocean temperatures rise in real time.
Sources
Malanoski, C.M., Finnegan, S., Huang, E.C., Blake, L., Mac Niocaill, C., & Saupe, E.E. (2026). Paleogeography modulates marine extinction risk throughout the Phanerozoic. Science, 391(6782), 285–289. https://doi.org/10.1126/science.adv2627
University of Oxford / EurekAlert. (15 January 2026). Fossils reveal ‘latitudinal traps’ that increased extinction risk for marine species. https://www.eurekalert.org/news-releases/1112130
This article is based on “Paleogeography modulates marine extinction risk throughout the Phanerozoic” by Cooper M. Malanoski, Seth Finnegan, Edward C. Huang, Lila Blake, Connal Mac Niocaill, and Erin E. Saupe, published in Science on 15 January 2026. DOI: 10.1126/science.adv2627. The study was conducted at the University of Oxford in collaboration with the University of California Berkeley, Stanford University, University of Leeds, and the Smithsonian Tropical Research Institute.
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Jane holds a BSc in Biology from the University of Regina and a Master of Science in Bioscience, Technology and Public Policy from the Univesity of Winnipeg. Her reporting interests include Life Sciences, Physical Sciences and the Cosmos.