Jurassic Mammals Were Picky Eaters

It's not just toddlers that are picky eaters. Fossils from tiny prehistoric mammals reveal that these species developed new characteristics - such as better hearing and teeth capable of precise chewing - that led to very precise diets, according to a new study.

Researchers from the University of Southampton discovered fossil mammals in South Whales, dating back to the Jurassic Period 201 to 145 million years ago. After analyzing their jaw mechanics and fossil teeth, the study team determined that two of the earliest shrew-sized mammals - Morganucodon and Kuehneotherium - were not generalized insectivores but had already evolved specialized diets, feeding on distinct types of insects.

"None of the fossils of the earliest mammals have the sort of exceptional preservation that includes stomach contents to infer diet, so instead we used a range of new techniques which we applied to our fossil finds of broken jaws and isolated teeth," lead author Dr. Pamela Gill of the University of Bristol said in a news release. "Our results confirm that the diversification of mammalian species at the time was linked with differences in diet and ecology."

The team used synchrotron X-rays and CT scanning to analyze these tiny, two-centimeter jaws. Though the jaws were in many pieces, researchers were able to stitch them together to make a complete digital reconstruction. The results showed that Kuehneotherium and Morganucodon had very different abilities for catching and chewing prey.

This technology allowed the scientists to better understand "the biology and the ecology of animals long dead," according to study co-author Dr. Neil Gostling, from the University of Southampton.

Researchers also compared the fossil teeth to teeth of present-day, insect-eating bats. Patterns of microscopic pits and scratches - known as "microwear" - found in the fossil teeth indicated that both extinct species had differing, picky diets.

Morganucodon favored harder, crunchier food items like beetles while Kuehneotherium preferred softer foods such as scorpion flies.

"This study is important as it shows for the first time that the features that make us unique as mammals... were associated with the very earliest mammals beginning to specialize their teeth and jaws to eat different things," added researcher Emily Rayfield.

The study findings were published in the journal Nature.