Bats evolved diverse skull shapes due to echolocation, diet

Santana previously used microCT to study the evolution and mechanics of bite force in leaf-nosed bats, a large and diverse taxonomic family of bats from the Americas. In the current study, her group investigated a wider swathe of bat diversity. They performed microCT scans of skulls from 203 species across all 20 taxonomic families of bats. The skulls came from collections at the Burke Museum, the American Museum of Natural History, the Field Museum, the Smithsonian Institution and the Natural History Museum of Los Angeles County.

“Museum collections of bat specimens played a critical role in allowing us to sample so broadly across bats families and really dig into the evolution of such a diverse group,” said Arbour.

 The scans gathered detailed data on the 3D shape of the lower jaw for 191 species, and the cranium — the upper portion of the skull that includes the upper jaw and braincase — for 202 species. The researchers then used computational modeling to combine the microCT scan data on the skulls with data on the evolutionary relationships among the bat species, as well as ecological characteristics such as diet. Their analysis allowed them not just to compare skull differences among and within bat lineages, but also to focus on specific parts of the skull, like the lower jaw.

“It’s important to independently analyze different parts of the skull because some parts of the skull have many different jobs, which may constrain the changes they can undergo,” said Santana. “For example, the cranium has many functions, such as feeding, respiration and protecting the brain. The lower jaw is largely just involved in feeding, which could give it more freedom to evolve in response to dietary changes.”

The team’s analyses indicated that early in bat evolution — from about 58 million to 34 million years ago — echolocation was a primary driver of skull shape across bat families. Most bats use echolocation to hunt, forage and navigate in light-poor settings. Bats echolocate by emitting specific types of high-pitched sounds with the larynx and then hearing the echoes as those sound waves bounce off of objects in their path. The fossil record indicates that echolocation evolved in bats early, at least 52 million years ago. Since then, different bat families have evolved unique mechanisms for echolocation — such as projecting sounds through the nostrils instead of the mouth. One group, the megabats, even lost the ability to echolocate laryngeally.

Article Source: Burke Museum