Synchrotron X-rays and CT scanning of fossilized jaws and teeth show that two shrew-like mammals that lived during the Jurassic period were eating very different things. Morganucodon (left) favored harder, crunchier beetles and Kuehneotherium preferred softer foods such as scorpion flies—common at the time. (Credit: Pamela Gill)

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Jurassic mammals were picky eaters

Tiny shrew-like mammals that lived during the Jurassic period didn’t eat just anything.

By analyzing jaw mechanics and fossil teeth, researchers were able to determine that two animals from this period between 201 and 145 million years ago, Morganucodon and Kuehneotherium, developed better hearing and teeth capable of precise chewing—and liked to feed on distinct types of insects.

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“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,” says lead author Pamela Gill of the University of Bristol.

“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 reveal in unprecedented detail the internal anatomy of these tiny jaws, which are only 2cm in length. Because the jaws were in many pieces, the scans were “stitched together” to make a complete digital reconstruction. Finite element modeling, the same technique used to design hip joints and bridges, was used to perform a computational analysis of the strength of the jaws.

The scans showed that Kuehneotherium and Morganucodon had very different abilities for catching and chewing prey.

Beetles and scorpion flies

“The improvement in CT scanning, both in the instrumentation, at Light Source at the Paul Scherrer Institute in Switzerland where we scanned or even the µ-VIS Centre at Southampton, along with access for research of this kind, allows us to make inroads into understanding the biology and the ecology of animals long dead,” says Neil Gostling from the University of Southampton and coauthor of the study that is published in Nature.

“The questions asked of the technology do not produce ‘speculation,’ rather the results show a clearly defined answer based on direct comparison to living mammals. This would not be possible without the computational techniques we have used here.”

An analysis previously carried out on the teeth of present-day, insect-eating bats shows that the teeth of Morganucodon and Kuehneotherium had very different patterns of microscopic pits and scratches, known as “microwear,” indicating they were eating different things.

Morganucodon favored harder, crunchier food items such as beetles, and Kuehneotherium selected softer foods such as scorpion flies—which were common at the time.

“This study is important as it shows for the first time that the features that make us unique as mammals, such as having only one set of replacement teeth and a specialized jaw joint and hearing apparatus, were associated with the very earliest mammals beginning to specialize their teeth and jaws to eat different things,” says Emily Rayfield, a professor at University of Bristol.

The Natural Environment Research Council, UK funded the research.

Source: University of Southampton

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