New Zealand’s tuataras appear like somber iguanas. However these spiny reptiles are usually not truly lizards. As an alternative, they’re the final remnant of a mysterious and historic order of reptiles referred to as the Rhynchocephalians that largely vanished after their heyday within the Jurassic interval.
They usually really are the oddballs of the reptile household. Tuataras can dwell for greater than a century, inhabit chilly climates and are capable of slide their jaws forwards and backwards to shear via bugs, seabirds and one another. They even possess a rudimentary third eye under the scales on the highest of their heads which will assist them monitor the solar.
These weird traits make tuatara an evolutionary enigma, and a spotty fossil report of its long-lost kin has confounded paleontologists. Probably outcompeted by lizards and snakes, just about all Rhynchocephalians went extinct on the shut of the Mesozoic Period. Many left little greater than dusty tooth and jaw fragments behind.
It seems {that a} essential piece of this puzzle has been sitting in a museum drawer for many years. Whereas sifting via a backlog of fossils at Harvard College’s Museum of Comparative Zoology, Stephanie Pierce, the museum’s curator of vertebrate paleontology, and her group lately found the almost full skeleton of a lizardlike animal on a slab of stone sufficiently small to slot in the palm of their palms.
The outstanding fossil was found in 1982 throughout an expedition to the Kayenta Formation, a fossil-rich outcrop in northern Arizona. This band of purple rock was deposited throughout the early Jurassic interval when the dinosaur reign was in its infancy. Round this primeval floodplain, early dinosaurs just like the crested Dilophosaurus mingled with burly, crocodile-like creatures encased in armor. Underfoot scurried primitive, shrew-like mammals and this unusual new reptile.
Whereas fossils of the positioning’s early mammals garnered a lot of the preliminary curiosity, Dr. Pierce and Tiago Simões, a postdoctoral paleontologist at Harvard who specializes within the early evolution of lizards, have lastly studied this specimen in depth.
In an article revealed Thursday in Communications Biology, the scientists named the brand new animal Navajosphenodon sani. Each the genus and species title (which implies “outdated age” within the Navajo language) seek advice from the Navajo Tribe, who dwell within the space the place the fossil was discovered.
The scientists employed micro-CT scans to research the squashed fossil in three dimensions and digitally pieced collectively the flattened cranium like a puzzle.
Though its physique was lizardlike, the construction of its cranium resembled a tuatara. It sported related rows of sharp, interlocking tooth extending instantly from the jawbone. The cranium additionally possessed two holes behind the animal’s eye. This configuration is without doubt one of the key traits differentiating tuataras from lizards, who solely have one gap. The additional gap helps stabilize the cranium because the tuatara bites down and saws via prey.
“All of those options are fairly conspicuous to fashionable tuataras and are not like what’s seen in every other fashionable reptiles,” Dr. Simões mentioned. After a slew of statistical assessments, the group slotted Navajosphenodon close to the bottom of the tuatara lineage.
The fossil illustrates that the our bodies of recent tuataras emerged within the Jurassic period and have modified little in 190 million years. This helps the favored distinction that these remnant reptiles are “residing fossils.” However Dr. Simões emphasised the variations: As an example, fashionable tuatara jaws finish in a set of beaklike fused tooth which might be absent in Navajosphenodon.
In response to Kelsey Jenkins, a doctoral scholar at Yale who focuses on early reptile evolution, many lineages of Rhynchocephalians exhibited little change all through their historical past. Nonetheless, 200 million years is excessive. “The one issues which might be that extremely conserved are issues like horseshoe crabs and cockroaches — not a decent-sized reptile,” mentioned Ms. Jenkins, who was not concerned with the brand new research.
Researchers argue this lack of change could signify pure choice on overdrive. “Sluggish charges of evolution don’t essentially imply absence of evolution,” Dr. Simões mentioned. Principally, it’s the evolutionary equal of the adage: “If it ain’t broke, don’t repair it.”
Whereas the invention of Navajosphenodon helps flesh out an important chapter in tuatara evolution, a lot of this reptile’s again story stays hazy. With out extra fossil discoveries, it will likely be troublesome for scientists to find out precisely why these lone survivors seem to own evolutionary cheat codes.
“Why the fashionable tuataras and their lineages have advanced so slowly for such a protracted time frame is a much bigger query and a bit more durable to get at,” Dr. Pierce mentioned. “We’d like extra fossils.”