Unique Traits Help Mammals Survive • Earth.com

A recent study of the family tree of mammals from several mass extinctions reveals unexpected traits among survivors, challenging the long-held belief that generalist or „boring” mammals primarily endure such catastrophic events.

Survival of the Unspecialized

The researchers discovered that mammals that survived mass extinctions had unique and advanced traits for their respective eras. This contradicts the concept of „survival of the fittest”.

„The idea of ​​’survival of the fittest’ dates back to the 1800s, and the common wisdom was that common animals were less likely to go extinct. But we found that when compared to later generations, most survivors appeared to be common only in retrospect,” explained Ken Angelczyk, senior author of the Field Museum. .

„They were actually very advanced animals for their time, with new traits that helped them survive and may have provided them with evolutionary flexibility.”

Study focus

This revelation was supported by a large family tree of synapsids constructed by study co-lead author Spencer Hellert of Columbia College Chicago. Synapsids are a group of animals whose only members are mammals.

„The thought before was that every time a new group of mammals evolves, you start with a small generalist animal, because when disaster strikes, they keep trucking — they can hide anywhere, they can eat what’s around,” said study co-author. – said lead author Spencer Hellert. „A species of mammal that survives a mass extinction may not be as specialized as a panda that can only eat bamboo.”

Evolutionary radiations

Hellert’s comprehensive family tree, the largest of its kind, combines data from all previously established family trees for synapsids and provides a comprehensive and rigorous approach to summarizing information from various sources.

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The research team examined the evolutionary radiation in synapsids over time, focusing on the organisms’ diets and body size, and found that the pattern of survival did not rely solely on common traits. At some point, survivors were not the only large synapsids and generalist insectivores.

How did the research begin?

David Krasnickle, an assistant professor at the Oregon Institute of Technology, published a study in 2019 that highlighted the lineage of small, insect-eating mammals that survive challenging times. He reached out to Hellert and Angelczyk to see if this trend would apply to earlier mammals and their ancestors.

„We were very surprised — it’s well established that mammalian radiations go back and forth from these small insectivores into larger taxa, so I expected to see that as we went back through synapsid history. When we went back, that pattern disappeared,” Krasnickel said.

Novel properties

Upon closer analysis, the researchers found that some surviving species, initially thought to be unspecialized, actually possessed new traits.

For example, some dinosaur-era mammals had advanced teeth that were designed not only for cutting prey but also for grinding like mortars and pestles. This „fan” tooth structure may have provided a significant advantage in times of food scarcity, allowing these mammals to consume a wide range of foods.

Special animals

However, the study’s findings should not be interpreted as suggesting that specialized animals such as pandas, which have a bamboo-exclusive diet, are less likely to become extinct than more generalist species such as raccoons.

Instead, the research highlighted that the species that made it through mass extinctions had traits far from common.

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„Animals with novel characteristics, such as new dental features or jaws that are a little better at breaking down different food items, don’t really become ecologically responsible until the current, older lineage dies out,” Crossnickle said.

„Often you need an extinction event like what killed off the dinosaurs to knock out some of those older groups, and then that allows those curious animals to persist and diversify.”

Research implications

According to the researchers, the results of their study have broad implications for scientists’ understanding of how evolution works.

„We don’t know if there is a set of stable features that are common to the ancestors of evolutionary diversifications,” Angelczyk said.

„The fact that we see this problem in the diversification of mammals and their ancient relatives means that we need to examine other groups to see if the situation in mammals is the exception or business as usual.”

The study is published in the journal Natural Ecology and Evolution.

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