The fossilized skull and a model reconstruction.
Not all scientific insights require a $1.1-billion experiment to observe gravity waves, or demand a giant particle collider be buried under Europe. Sometimes all that's needed are a few bucks worth of modeling clay and toothpicks -- and, well, a pair of priceless 250-million-year-old fossils.
The fossils in question include an unusual reptilian skull, small but ending in a suddenly flaring mouth, like the face of a hammerhead shark or a fleshy harmonica. Within the strange maw were rows and rows of needle teeth, stumping the paleontologists who had unearthed it where a sea once covered parts of China, millions of years ago.
The breakthrough came when they decided to reconstruct the creature's head in brightly-colored putty. "The jaw arrangement is very unusual, and we needed to be sure that hypothesis as to how the jaw would close really would work," said Nick Fraser, an expert on Triassic animals at the National Museum of Scotland and an author of a study recently published in the journal Science Advances, told The Washington Post.
The reptile used its flared mouth to scrape away algae and plants from submerged rocks, and then it sucked down the watery mix. " By gulping in this liquid mix of plant matter and sea water, the animal could close its mouth," Fraser said, "and, using its tongue, force the water out of the side off the mouth and across the filter formed by the needle-shaped teeth." The final clue was a row of chisel-like teeth at the leading edge of the jaw, which are similar to those of dinosaurs believed to have eaten plants. (Atopodentatus unicus wasn't a dinosaur, however -- those would arrive a few million years later.)
The work by Fraser and his colleagues overturn a 2014 hypothesis that A. unicus was even more bizarre. A previously-discovered specimen appeared to have a bifurcated snout that fit together vertically, like the teeth of a zipper. That struck Li Chun, an author of the Science Advances report and a paleontologist at Institute of Vertebrate Paleontology and Paleoanthropology in China, as a bit farfetched -- even for the weirdness of the early Triassic period. In his view, Li wrote to The Washington Post in an email, the 2014 skull was crushed and too badly preserved reconstruct its original structure.
Fraser said he understands how the first paleontologists ended up at the wrong conclusion. Thanks to the pair of new fossils, which appear to be in much better condition, Fraser's confident this model is closer to the truth. "We're certain we have this particular aspect of the animal correctly." There's still plenty of mystery left, however: No one knows what the a juvenile Atopodentatus was like, or how they mated.
Even without a vertical zipper mouth, Atopodentatus unicus is still an odd beast. There are very few reptilian herbivores in the sea -- modern-day examples include the marine iguana, the green turtle and not a whole lot else.
To hear Fraser tell it, Atopodentatus unicus owed its unique existence to death -- and lots of it. The reptile lived in the early Triassic, in the wake of the Permian extinction event. Known also as the Great Dying, the Permian extinction was a point in time when nine in every 10 marine species vanished. Many previously-full ecological niches were left wide open, prompting an evolutionary free-for-all, including Atopodentatus unicus and the tusked mammal ancestor Dicynodon .
"You had a wiping of the slate," Fraser said, and then a period of biological experimentation. "There was an explosion of new life forms, and they were crazy."
© 2016 The Washington Post
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