In Kuwajima, Japan, researchers unearthed a plethora of fossils from the Cretaceous period. Dinosaurs, reptiles, plants, mammals, and fish were all represented in the haul. But peppered throughout the geologic layer, scientists also found more than 250 teeth from a creature that represented an evolutionary link between reptiles and mammals.
Dubbed Montirictus kuwajimaensis, the creature is part of an animal family called tritylodontids. Previously, scientists thought these herbivorous animals didn’t live for long besides their mammal counterparts, as they were outcompeted by mammals for natural resources. But a new study published in the Journal of Vertebrate Paleontology suggests tritylodontids lived 30 million years longer than previously thought.
“Tritylodontids were herbivores with unique sets of teeth which intersect when they bite,” said study author Hiroshige Matsuoka, of Kyoto University, in a statement. “They had pretty much the same features as mammals—for instance they were most likely warm-blooded—but taxonomically speaking they were reptiles, because in their jaws they still had a bone that in mammals is used for hearing.”
Tritylodontids species, it appears, had a fairly global distribution during their heyday. They lived and expanded their reach during the Jurassic era.
“Usually fossils are identified as a new species only when a relatively complete set of structures like a jaw bone are found. In these cases, characteristics of teeth tend to be described only briefly,” said Matsuoka. “Tritylodontid teeth have three rows of 2-3 cusps. This time we paid attention to fine details like the size and shape of each cusp. By using this method it should be possible to characterize other species on the evolutionary tree as well.”
The researchers hope to continue excavating the Kuwajima site, and learn more about Montirictus kuwajimaensis and the area’s ancient ecology.
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