As an expert in the body size evolution of animals, professor of Biology at The University of New Mexico Felisa Smith is often called on to lend her knowledge and opinion on the subject. She is co-editor of a book about animal size and has rung in on subjects ranging from teenage Tyrannosaurus rex to fictional sandworms in the movie Dune.

Felisa Smith
Professor Felisa Smith

Most recently, in a Perspective article published in the prestigious journal Science, Smith examined new research titled Brawn before brains in placental mammals after the end-Cretaceous extinction and offered her own viewpoint. Her article provides context and “a pithy discussion of where this work fits in the larger scientific framework.”

The research looked at mammals, which have the largest ratio of brain to body size (encephalization) among vertebrates and the belief this relationship emerged early on in mammalian evolution, with enlarging brains leading the way into new and diverse forms. However, the research team found instead that body sizes were the first to increase. It was only later, that brain size began to increase, “likely driven by a need for greater cognition in increasingly complex environments. This led to the highly encephalized brains of today, including those of humans.”

Smith’s essay, The road to a larger brain, looks at the trade-offs associated with growing a larger brain, the topic of the Brawn before brains research.

“Brains are energetically expensive, which means that if you had two animal of the same size, the one with the larger brain would require much more energy (food) to survive. Because energy is often limiting for animals, this means that other activities, and especially reproduction, are scaled-down. Indeed, animals with relatively larger brains for their bodies have lower reproductive rates”, Smith said.

In the study, the researchers looked at what happened right after the extinction of the non-avian dinosaurs at the K/Pg. Smith’s lab has shown that mammal body size diversified almost exponentially at this time as they began to occupy all the newly vacated niches.

“But did brain size also increase proportionately?” she continued. “The study, it turns out, showed that it didn’t. Essentially mammals got bigger and ‘dumber’ first. Once these body size niches were all full, then there was strong selection on brain size and mammal brain size increased.”

“The article I wrote is a bit different because it’s something they asked me to write, a review really, not original research,” Smith explained. “Science often invites scientists knowledgeable in a field to write an essay about a topic that is being published in the journal. In this case, because the article talked about mammal brain and body size evolution, and I am an expert in the latter, they asked me to write it… I was very excited about the study in the journal because it confirms some ideas we’ve had about the role of ecology in driving the early evolution of mammals right after the extinction of non-avian dinosaurs.”

Smith is the president-elect of the American Society of Mammalogists, the oldest and largest mammal society in the world. She is only the fifth woman and the first Hispanic woman to be elected to the position. She is also currently the president of the International Biogeography Society, the main society for scientists studying biodiversity and the geographical distribution of plants and animals around the globe.

Her book, Mammalian Paleoecology: Using the Past to Study the Present, was released last year by Johns Hopkins University Press.

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