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This Ancient Reptile Is Not a Lizard. Don’t Call It a Lizard

An orange-green lizard eats an insect in this illustration.

150 million years in the past, a prehistoric reptile not like fashionable lizards slinked round what’s now Wyoming. An historical rhynchocephalian, the insect-eating animal’s discovery might make clear the persistence of its dwelling relative, the tuatara.

The reptile is called Opisthiamimus gregori. It appears to be like like a lizard, however like New Zealand’s tuatara, it isn’t one. Lizards are squamates, an order of reptiles that features snakes and worm lizards. Rhynchocephalians are a definite group that diverged from lizards within the Triassic Interval.

The fossils of Opisthiamimus come from Wyoming, the place they sat above what was as soon as an allosaurus nest. Paleontologists discovered 4 specimens on the website, together with a virtually full articulated skeleton of the reptile. The newly found species is described in a examine printed at the moment within the Journal of Systematic Paleontology.

“What [the fossil] does is hammer house the truth that rhynchocephalians have been a really numerous group for lots of their evolutionary historical past,” mentioned examine co-author Matthew Carrano, the curator of Dinosauria on the Smithsonian’s Nationwide Museum of Pure Historical past, in an electronic mail to Gizmodo. “There’s doubtless extra ‘hidden range’ on the market, as a result of so lots of the fossils are small and fragmentary, and arduous to determine.”

The fossilized reptile's remains.

Final 12 months, scientists described a rhynchocephalian known as Taytalura alcoberiserving to to make clear the evolutionary divergence between their reptilian order and squamates. Taytalura is barely recognized from a well-preserved cranium, however the youthful Opisthiamimus has a virtually full skeleton. Its discovery builds on that of Taytalura by displaying that their reptilian order was numerous comparatively early in deep time.

“I agree with the authors that this is a crucial discovering from the Morrison Formation,” mentioned Tiago Simões, an evolutionary biologist at Harvard College who was not affiliated with the current paper, in an electronic mail to Gizmodo. Simões was one of many researchers who labored on it Taytalura.

Opisthiamimus may be very historical; its existence precedes Tyrannosaurus rex by 60 million years. It lived within the late Jurassic, alongside Archeopteryx and Stegosaurus (although a lot nearer to the bottom than the previous two, and far smaller, measuring simply 6 inches from nostril to tail.)

The one extant rhynchocephalian is the tuatara, a part of the subgroup known as the sphenodonts, of which there are two species. The tuatara can reside over 100 years and has the fastest-moving sperm of any reptile. It notably has a parietal eye within the heart of its brow and three rows of enamel: two in its higher jaw and one within the decrease. Not like different reptiles, rhynchocephalian enamel are a part of their jaws, reasonably than separate, replaceable components.

Due to its distinctive anatomy, the tuatara is sometimes called a ‘dwelling fossil.’ It has endured when all different members of its order couldn’t. However do not name it primitive: It merely discovered a profitable system for survival and caught with it.

A foot-long beige reptile sits on the ground.

“I might be cautious with the phylogenetic interpretation the authors offered for this species,” Simões added, noting that options of Opisthiamimus are extra typical of sphenodontians that seem later within the fossil report.

Discovering extra fossils of the traditional reptiles might assist clarify why squamates persist on Earth in abundance whereas rhynchocephalians don’t.

“One concept is that a number of of the distinctive options of squamates allowed them to outcompete rhynchocephalians,” Carrano mentioned. “There is a broad sample of gradual decline in rhynchocephalians alongside a gradual improve in squamate range. However competitors occurs inside environments, and proper now we do not have sufficient fossils to actually examine that concept, though in a spot just like the Morrison Formation we’re getting shut.”

Now, the staff is sifting via the stays of the Allosaurus nest discovered slightly below Opisthiamimus. Extra rhynchocephalian fossils await discovery, within the Morrison Formation and past. Once they come to mild, they may assist us unpack their reptilian household tree.

Extra: Uncommon Fossil of Triassic Reptile Found in Antarctica


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