Hot and Cold: Crocodile Evolution Based on Ocean Temps

Ancient crocodiles colonized the seas during warm phases and became extinct during cold phases, according to a new study, demonstrating a link between crocodile evolution and ocean temperature.

For more than 140 million years, crocodiles have been operating this way, but why would they move in this manner only to become extinct later?

Only 23 species of crocodiles live today, but there were once hundreds of species roaming the Earth. On four occasions in the past 200 million years, major crocodile groups entered the seas, and then became extinct.

This new study suggests that crocodiles repeatedly colonized the oceans at times of global warming.

"We thought each of these evolutionary events might have had a different cause. However, there seems to be a common pattern," lead author Dr. Jeremy Martin said in a statement.

Martin, along with a team of paleontologists and geochemists, compared the evolution of the number of marine crocodilian fossil species to the sea temperature curve during the past 200 million years. This temperature curve has previously been used to reconstruct past environmental conditions.

"The seawater temperatures derived from the composition of fish skeleton thus corresponds to the temperature of water in which the marine crocodiles also lived," co-author Christophe Lécuyer explained.

The results showed that 180 million years ago, when the oceans warmed, crocodiles correspondingly flocked to these oceans. These first marine crocodilians became extinct about 25 million years later, during a period of global freezing. Then, another crocodilian lineage emerged and colonized the marine environment during another period of global warming, and so on and so forth.

Environmental temperatures, based on these findings, clearly are linked to the evolutionary process of these reptiles.

"This work illustrates a case of the impact of climate change on the evolution of animal biodiversity, and shows that for crocodilians, warming phases of our earth's history constitute ideal opportunities to colonize new environments," added co-author Michael Benton from the University of Bristol.

The study findings are described in the journal Nature Communications.