Big-brained mammals have higher risks of extinction, with the smallest animals most vulnerable to being wiped out, a new study found. Moreover, mammals with more spacious skulls have a longer life span.

Stanford University professor Eric Abelson hypothesized a link between extinction risks and bigger brains. He investigated museum samples of more than 1,650 animals across 160 species found in the United States but excluded marine mammals.

Abelson's analysis covered various species from rats to buffalos. He measured the animals' cranium and body sizes and checked their standing in the International Union for Conservation of Nature's (IUCN) list of endangered species around the world. Abelson also examined another set of more than 600 species found around the world.

The research revealed a pattern where big-brained animals are more likely to become extinct. Among the species in North America, the link is stronger for mammals whose big brain is relative to the size of their bodies.

These animals are, if not extinct, either protected or endangered due to low population. Small-bodied mammals with large brains carry the highest extinction risk.

In particular, short-eared dog (Atelocynus microtis) and the tiger cat (Leopardus tigrinus) both have large brains but are considered as near threatened species by the IUCN. The Cozumel raccoon or pygmy raccoon (Procyon pygmaeus) is known for its large brain and is currently critically endangered in the Cozumel Island in Mexico.

However, the association isn't as strong in very large mammals. Abelson suggests that species who are able to travel and adapt to new environments easily benefit from the huge costs of having bigger brains.

In a previous research from Spanish National Research Council's Daniel Sol, findings showed that big-brained birds have higher survival rates compared to their smaller-brained counterparts.

"This likely represents a case of 'endangerment filtering.' Species in North America have gone through a period where large-bodied species had suffered large population losses," notes Abelson, who believes that more research into the link between body and brain sizes can provide the scientific community with new ways to predict the rate of extinction among animals.

"Right now, conservation efforts could benefit from better predictions of which animals might become endangered in the future," says Abelson, who is also a scientist at the Pacific Southwest Research Station of the U.S. Forestry Service.

The research was published in the journal Proceedings of the Royal Society B: Biological Sciences on Feb. 17.

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