Sep 6, 2025 08:00 PM
https://cosmosmagazine.com/nature/animal...-evolution
EXCERPTS: A deep dive into the world of rodent thumbs could help explain why the creatures spread and thrived all over the world.
The research examined hundreds of rodents in museum collections to track the evolution of their thumbnails. Many rodents have evolved smooth, flat nails rather than curved claws on their thumbs. But until now, no one had documented this trend across the evolutionary tree.
[...] “Using that information, we reconstructed the rodent family tree in terms of rodents that handle food with their hands versus ones that only use their mouths.”
For example, guinea pigs, which do not have thumbnails, don’t usually eat food with their hands. However, rodents that have thumbnails, like squirrels, often use their hands to nibble away on nuts and fruits.
The thumbnail-having rodent ancestor may help explain why modern rodents can be found on every continent except for Antarctica.
“Nuts are a very high-energy resource, but opening and eating them requires good manual dexterity that a lot of other animals don’t have,” says Feijó. “Maybe rodents’ thumbnails allowed them to exploit this unique resource and then diversify broadly, because they were not competing with other animals for this food.”
Primates like humans are the only mammals other than rodents to have evolved nails rather than claws on their thumbs. “When I got involved with this project looking at rodents’ nails or claws, I immediately thought about their life modes – where they live, how they use their hands in ways beyond just eating,” says Missagia.
“I knew that primates, which mostly have nails, are usually arboreal, they live in trees. We tested that correlation as well, and we found that rodents with nails also were more likely to live above ground or in trees, while fossorial rodents, the ones that dig, were more likely to have claws and not nails on their thumbs.”
Thumbnails likely developed in primates independently from rodents in a process called convergent evolution... (MORE - missing details)
EXCERPTS: A deep dive into the world of rodent thumbs could help explain why the creatures spread and thrived all over the world.
The research examined hundreds of rodents in museum collections to track the evolution of their thumbnails. Many rodents have evolved smooth, flat nails rather than curved claws on their thumbs. But until now, no one had documented this trend across the evolutionary tree.
[...] “Using that information, we reconstructed the rodent family tree in terms of rodents that handle food with their hands versus ones that only use their mouths.”
For example, guinea pigs, which do not have thumbnails, don’t usually eat food with their hands. However, rodents that have thumbnails, like squirrels, often use their hands to nibble away on nuts and fruits.
The thumbnail-having rodent ancestor may help explain why modern rodents can be found on every continent except for Antarctica.
“Nuts are a very high-energy resource, but opening and eating them requires good manual dexterity that a lot of other animals don’t have,” says Feijó. “Maybe rodents’ thumbnails allowed them to exploit this unique resource and then diversify broadly, because they were not competing with other animals for this food.”
Primates like humans are the only mammals other than rodents to have evolved nails rather than claws on their thumbs. “When I got involved with this project looking at rodents’ nails or claws, I immediately thought about their life modes – where they live, how they use their hands in ways beyond just eating,” says Missagia.
“I knew that primates, which mostly have nails, are usually arboreal, they live in trees. We tested that correlation as well, and we found that rodents with nails also were more likely to live above ground or in trees, while fossorial rodents, the ones that dig, were more likely to have claws and not nails on their thumbs.”
Thumbnails likely developed in primates independently from rodents in a process called convergent evolution... (MORE - missing details)