A recent study reveals the fascinating evolutionary journey of bat teeth and jaws. With over 200 species mostly found in the American tropics, noctilionoid bats possess a wide variety of jaw structures that have adapted to different diets.
The research emphasizes the remarkable, yet systematic, changes in the number, size, shape, and positioning of teeth in these bats.
The experts found that bats with shorter snouts seem to have fewer teeth due to space constraints. Meanwhile, those with elongated jaws can accommodate more teeth, much like the ancestors of placental mammals.
According to the researchers, comparing noctilionoid species can reveal a lot about how mammalian faces evolved and developed, particularly jaws and teeth.
“Bats have all four types of teeth – incisors, canines, premolars and molars – just like we do,” said study co-author Sharlene Santana, a professor at the University of Washington. “And noctilionoid bats evolved a huge diversity of diets in as little as 25 million years, which is a very short amount of time for these adaptations to occur.”
However, the underlying factors that propelled this rush of dietary diversification in these bats remain a mystery. Today, different noctilionoid species have varied diets ranging from insects, fruit, and nectar to fish and even blood.
Alexa Sadier, the lead author and an incoming faculty member at the Institute of Evolutionary Science of Montpellier, emphasized the intriguing diversity in these species.
“There are noctilionoid species that have short faces like bulldogs with powerful jaws that can bite the tough exterior of the fruits that they eat. Other species have long snouts to help them drink nectar from flowers. How did this diversity evolve so quickly? What had to change in their jaws and teeth to make this possible?”
To investigate, the research team employed CT scans and various techniques to examine the jaws, premolars, and molars of over 100 noctilionoid bat species.
The study’s findings showed that “developmental rules” existed, determining the appropriate teeth assortment based on the bat’s diet.
Bats with long or intermediate jaws generally had the standard set of three premolars and three molars on each jaw side. However, those with shorter jaws, often fruit eaters, would typically lose either the middle premolar or the back molar or even both.
“When you have more space, you can have more teeth,” said Sadier. “But for bats with a shorter space, even though they have a more powerful bite, you simply run out of room for all these teeth.”
For short-jawed bats, the limited space could explain the presence of broader front molars. “The first teeth to appear tend to grow bigger since there is not enough space for the next ones to emerge,” said Sadier.
“This project is giving us the opportunity to actually test some of the assumptions that have been made about how tooth growth, shape and size are regulated in mammals,” said Santana. “We know surprisingly little about how these very important structures develop!”
Most mammalian tooth development studies have been conducted on mice, which possess only molars and highly adapted incisors. It’s still uncertain if the same genetic and developmental patterns control tooth growth in mammals with more “ancestral” tooth sets, like bats and humans.
As the project continues, Sadier, Santana, and their colleagues aim to expand their study to include noctilionoid incisors and canines. Their goal is to uncover more about the genetic and developmental mechanisms shaping tooth development in this bat group.
“We see such strong selective pressures in these bats: Shapes have to closely match their function,” said Santana. “I think there are many more evolutionary secrets hidden in these species.”
The study is published in the journal Nature Communications.
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