The discovery of a lizard-like fossil with bizarre teeth is challenging public perceptions of an iconic animal in New Zealand.
Oenosaurus—meaning “wine lizard”—inhabited the earth around 150 million years ago, during the era of Allosaurus, Brachiosaurus, and Stegosaurus. The fossil was named for the wine-producing part of Germany in which it was found, but its closest living relative is the tuatara, an unusual reptile native to New Zealand.
The only surviving member of an ancient lineage called rhynchocephalians, tuatara resemble iguanas but are not true lizards—in fact, iguanas are more closely related to snakes.
The skull of Oenosaurus, whose discovery was announced last month in the journal PLoS ONE, defies the long-standing notion of the tuatara as “a living fossil” by demonstrating impressive diversity in its evolutionary lineage.
The owners of a limestone quarry in Bavaria, Germany, found the fossil. Recognizing its significance, they donated it to a nearby paleontological research institute.
It’s not that uncommon, lead author Oliver Rauhut explained, for private collectors to discover fossils that are new to science, but often they prefer to keep or auction the best ones they find. The owners of this quarry, however, “wanted everything they found to be seen by scientists.”
“I wasn’t surprised at a new fossil being found in Germany,” said Marc Jones, a paleontologist who specializes in tuatara fossil relatives. “However, I was quite excited when I first heard about its bizarre teeth.”
Instead of sharp individual teeth, Oenosaurus sported large, fused tooth “plates” on top and bottom. The flat plates spanned the jaw, forming a crushing surface, and grew throughout the course of Oenosaurus’ life. Inside the sturdy tooth plates, X-ray scans revealed more interesting details: a profusion of tiny, hollow tubes packed together in no clear pattern.
Modern tuatara are carnivorous, their mouths equipped with one row of pyramidal teeth on bottom and two rows on top for cutting and tearing food such as crickets. The plate teeth of their extinct relatives, however, were better suited to crushing shells. Scientists believe that Oenosaurus fed on a diet of mollusks and crabs if it was a marine animal, or, more likely, snails and thick-shelled insects if it was terrestrial.
Only chimaerans and lungfish, two very old fish groups, have teeth today that are similarly shaped. The fossil record shows even less evidence of plate teeth, making Oenosaurus a unique specimen in the realm of reptiles.
For such teeth to evolve, tuatara’s predecessors had to have an unexpected amount of “evolutionary plasticity,” or ability to adapt to new circumstances. This runs counter to the long-held idea that tuatara are among the most primitive of reptiles, descending unchanged through hundreds of millions of years. “One of the points we wanted to make was that this group has a long history and a very successful history,” explained Rauhut.
For several decades, paleontologists have been filling out the evolutionary tree of rhynchocephalians with new fossils. Some of tuatara’s extinct relatives were long-legged insectivores; others had grinding teeth for eating plants; still others were aquatic fish-eaters.
None were quite like Oenosaurus, but all attest to what paleontologists now recognize as a highly diverse family—one that was not necessarily inferior, as previously believed, to the lizard, snake, and mammal groups that had begun to proliferate at the end of the Mesozoic era.
This understanding of the fossil record has been largely ignored or unknown outside of paleontology, however. Especially in New Zealand, where the tuatara is a beloved species, expert Marc Jones believes it will be challenging to change the public perception of the animal as a living fossil. “Explaining to people the context of certain fossils can be quite complicated because they may not have any closely related or well known living relatives,” he said.
With tuatara making recent headlines, though, now might be a good time to try. A high-profile study in Nature this summer predicted that climate change could lead to the tuatara’s extinction within decades. Efforts to reintroduce tuatara to islands off New Zealand’s coast this fall were also publicized.
Tuatara’s lineage has survived many glaciations, sea level rises, and climate changes in the millions of years it’s been on earth. Unfortunately, that doesn’t mean tuatara are less vulnerable to global environmental change now.