Researchers studying bat skulls reveal that the carnivorous ones who eat vertebrates – like frogs, lizards, birds, mice, and other bats – are larger and produce stronger bite forces than those who feed on insects and fruit. Vertebrate-eating bats without wide gapes eat only fish. The findings, "Go Big Or Go Fish," are published in Proceedings of the Royal Society B this week.
There are lots of predatory mammals, but specialized carnivory is uncommon. That’s when vertebrate prey is the primary energy source, and it evolved multiple times in bats. The transition from eating insects to chomping on other animals with backbones occurred at least six times in the evolutionary history of bats. "Vertebrate prey are a unique challenge for carnivorous bats," University of Washington’s Sharlene Santana said in a statement. "They eat flesh, bones and everything else within their prey, and we wanted to understand the evolutionary changes that help them accomplish this."
To study the divergence of carnivorous bats from their insectivorous ancestors, Santana and colleagues took high-resolution photographs of the skulls and lower jaws of 140 bats spanning 35 species, and then they conducted a computer-based comparison of various landmarks. Skulls and lower jaws provide attachment points for muscles, and by studying variations in attachment sites, the researchers could compare the bats’ bite force and their gape.
From left to right, these are skulls of insectivorous, carnivorous, and fish-eating bats. Sharlene Santana
Carnivorous bats are larger, and their skull shapes enhance their bite force at wide jaw gapes. Surprisingly, the team found that fish-eating bats are anatomically distinct from bats with terrestrial prey. The skulls of piscivores are optimized for a strong bite force at a narrow jaw gape. "Many fish have flatter bodies compared to land vertebrates, which may explain the distinctive jaws and bite force of fish-eating bats," Santana explained. "In addition, fish-eating bats must spend a lot of time chewing the carcass thoroughly, breaking up those sharp and tiny bones into chunks that are easier to swallow and digest."
The team also compared bat skulls to that of other carnivores, including lions, hyenas, wolves, and weasels. The skulls do resemble each other, suggesting that meat-eating mammals likely converged on skull shapes. However, bat skulls are well suited for increased bite force production at the expense of gape. Unlike big cats and polar bears, bats don’t tear at flesh with their teeth: They eat the whole prey, backbone and all.