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New Zealand’s tuatara look like gloomy iguanas. But these spiny reptiles aren’t actually lizards. Instead, they are the last remnants of a mysterious and ancient order of reptiles known as the Rhynchocephalians, which disappeared after their heyday during the Jurassic period.
And they really are the weirdos of the reptilian family. Tuataras can live for over a century, living in cold climates and slide your jaws back and forth insects, seabirds and each one. They even have a primitive structure third eye Under the scales on their heads that can help them follow the sun.
These peculiar features make the tuatara an evolutionary conundrum, and the spotty fossil record of its long-lost relative is confusing paleontologists. Nearly all Rhynchocephalians, probably left behind by lizards and snakes, became extinct at the end of the Mesozoic Era. Many left little more than dusty bits of teeth and jaws behind.
It turns out that an important piece of this puzzle has been sitting in a museum drawer for decades. While examining fossils accumulated at Harvard University’s Museum of Comparative Zoology, Stephanie Pierce, the museum’s curator of vertebrate paleontology, and her team recently discovered the nearly complete skeleton of a lizard-like animal on a stone slab small enough to fit in a palm. from your hands.
The remarkable fossil was discovered in 1982 during an expedition to the Kayenta Formation, a fossil-rich rock in northern Arizona. This group of red rocks was deposited during the early Jurassic period, when the dinosaur reign was in its infancy. Around this primeval floodplain, early dinosaurs such as the crested Dilophosaurus mingled with burly, crocodile-like creatures covered in armor. Underfoot, primitive, shrew-like mammals and this strange new reptile frightened.
While fossils of the first mammals in the area have garnered much of the initial attention, Dr. Pierce and Tiago Simões finally delved into this example.
In an article published Communication Biology on Thursday, scientists named the new animal Navajosphenodon sani. Both the genus and species name (meaning “old age” in the Navajo language) refer to the Navajo Tribe that lived in the area where the fossil was found.
The scientists used micro-CT scans to probe the crushed fossil in three dimensions and digitally put the flattened skull together like a jigsaw puzzle.
Although its body was lizard-like, the structure of its skull resembled a tuatara. It had similar rows of sharp, interlocking teeth extending directly from the jawbone. The skull also had two holes behind the animal’s eye. This configuration is one of the main features that distinguishes tuatara from lizards that only have one hole. The extra hole helps stabilize the skull as the tuatara bites and cuts through its prey.
Dr. “All of these features are quite remarkable for modern tuatara and are unlike those seen in other modern reptiles,” Simões said. After a series of statistical tests, the team placed Navajosphenodon near the base of the tuatara lineage.
The fossil shows that the bodies of modern tuatara emerged during the Jurassic period and have changed little in 190 million years. This supports the popular distinction that these relic reptiles are “living fossils.” However, Dr. Simões emphasized the differences: modern tuatara jaws, for example, end with a set of beak-like fused teeth not found in Navajosphenodon.
According to Kelsey Jenkins, a doctoral student at Yale who specializes in early reptilian evolution, many lineages of Rhynchocephalians have changed little over the course of their history. However, 200 million years is excessive. “The only things that have been so well preserved are things like horseshoe crabs and cockroaches — not a properly sized reptile,” said Ms. Jenkins, who was not involved in the new study.
The researchers argue that this lack of change may represent extreme speed of natural selection. Dr. “Slow evolution rates don’t necessarily mean evolution didn’t happen,” Simões said. Basically, it’s the evolutionary equivalent of the adage “If it’s not broken, don’t fix it”.
Although the discovery of Navajosphenodon helped reveal a pivotal chapter in tuatara evolution, much of this reptile’s back story remains unclear. Without more fossil discoveries, it will be difficult for scientists to determine exactly why these solitary survivors possessed evolutionary cheat codes.
Dr. “Why modern tuatara and their descendants evolved so slowly over such a long period of time is a bigger question and a little harder to understand,” Pierce said. “We need more fossils.”
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