It’s likely you’ve already chewed and swallowed some tasty morsel today. But when did that ability emerge? New evidence points to at least the middle Jurassic, back when dinosaurs still reigned.
Transcript
SCOTT SIMON, HOST:
When you eat, you chew – (imitating chewing) – and swallow. You’ve masticated. It’s an ability that modern mammals share, including BJ Leiderman, who writes our theme music. New evidence suggests this ability goes back to the time when dinosaurs roamed the earth. Here’s NPR science reporter Ari Daniel.
ARI DANIEL, BYLINE: Over the years, a swath of the Inner Mongolia region of China has coughed up heaps of remarkable fossils.
ZHE-XI LUO: To say it’s a hot spot is actually understatement.
DANIEL: A decade ago, a specimen in a thick slab of shale caught the eye of University of Chicago paleontologist Zhe-Xi Luo. It was the fossilized bones and fur of an ancient mammal the size of a Chihuahua.
LUO: Early fossil mammals are exceedingly rare.
DANIEL: The fossil was hard to see against the rock, so one of Luo’s colleagues basically snapped a vivid image of it using X-rays.
LUO: It would then make this bone pop out in different colors.
DANIEL: And it captured a curious combo of characteristics. The back end resembled a modern-day platypus, meaning the animal – living roughly 165 million years ago – was likely semiaquatic.
LUO: However, its teeth and jaw would be very different from platypus. So the head is very much of a predator.
DANIEL: Then there was the other thing that Luo noticed about that fossil.
LUO: Tiny hyoid bones.
DANIEL: The human hyoid bone sits in our throat, half an inch or so above our Adam’s apple, and supports the back side of our tongue. The team later CT-scanned the fossil, including the underside of the skull, which exposed a delicate roof of the mouth, along with a series of rarely preserved bone hooks and ridges.
LUO: And with that, we are able to reconstruct the whole muscular-skeletal machinery.
DANIEL: Which revealed that this animal, which the researchers named Megacauda sungei, was likely capable of doing two things unique to mammals. The first is chewing food and then swallowing it. Other vertebrates tend to bite and gulp, but mammals…
LUO: Chew down all the food with our teeth, and we swallow one bolus down our esophagus at a time.
DANIEL: Secondly, this fossil appears to have been able to suckle.
LUO: That ability to suckle mother’s milk literally defined our biology. Mammals are named after the mammary glands.
DANIEL: This is some of the oldest evidence of an animal with both these abilities, meaning that the origin of these innovations lies deep in the past. The results are published in the journal Nature.
JESSICA THEODOR: Oh, it’s a fascinating specimen.
DANIEL: Jessica Theodor is a paleontologist at the University of Calgary who wasn’t involved in the research. She says such a fossil tracks the evolution of lactation, which she likens to a kind of dietary and hormonal conversation between mother and baby.
THEODOR: The conversation is beginning very far back, in the Jurassic and Cretaceous. That’s amazing to me – that it’s this old and this fundamental.
DANIEL: For Zhe-Xi Luo, this fossil’s the latest evidence of how new ways of feeding have helped mammals and their predecessors diversify, even when they were the little guys on the block.
LUO: They’re never dominant in the age of dinosaurs, but they hold out relatively well compared to all other vertebrates.
DANIEL: In the Jurassic, there were already gliders and swimmers and tree dwellers and subterranean protomammals, each one making its own kind of living, united in their shared ability to chew, swallow and suckle.
Ari Daniel, NPR News.
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