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110 Million-Year-Old Lizard Trapped In Amber Is A Previously Unknown Species

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Stephen Luntz

Freelance Writer

clockMar 17 2022, 16:37 UTC
amber lizard

At 110 million years old this is one of the oldest vertebrates where we have more than just bones and teeth. It's also a previously unknown species. Image Credit: Adolf Peretti and the Peretti Museum Foundation.

Forget producing dinosaurs using DNA from mosquitoes trapped in amber, how about if the dinosaurs themselves got trapped? OK, we're not there yet, but scientists have found a lizard that lived at the peak of the dinosaurs' reign that got trapped in tree resin, and it's a species unknown from more conventional fossils.

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In Scientific Reports, a team including Dr Juan Daza of Sam Houston State University describes a small lizard distantly related to modern skinks that was found trapped within a lump of amber in Myanmar. Its outstanding preservation gives us an unbeaten insight into a reptile from 110 million years ago.

“We had the rare opportunity of studying the articulated skeleton, but also describing the external appearance of the lizard (scalation), in the same way that herpetologists (amphibian and reptile specialists) study modern species,” Daza said in a statement

The lizard is a juvenile and perhaps had yet to learn how to avoid the encroaching tree sap that brought its life to an untimely end, but granted it a form of immortality. It was found at Hkamti (Myanmar), separated by 100 kilometers (60 miles) and 10 million yeas from the famous amber mines at Hukawng, which has provided most of the world's Cretaceous vertebrates with soft tissues preserved in amber.

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A) Fossil Retinosaurus hkamtiensis embed in amber, B) 3D model of the body dorsal scales, C) Detail of the ventral scales of the head, D and E) Lateral views of the head. CT reconstructions by Edward Stanley using synchrotron data gathered at Imaging and Medical Beamline at the Australian Synchrotron in Melbourne. Image Credits: Adolf Peretti and the Peretti Museum Foundation.

Daza and co-authors have named it Retinosaurus hkamtiensis (Amber lizard from Hkamti) and consider it a member of the Scincoidea superfamily of lizards. Besides skinks, the Scinocoidea include armored lizards and night lizards (Xantusiidae), which at least superficially are the most similar modern-day equivalents to Retinosaurus.

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That similarity is interesting, because today night lizards only live in North and Central America, about as far from South East Asia as you can get. At the time, however, Hkamti was not part of mainland Asia. The so-called “Burma Block” was originally part of the supercontinent Gondwana, attached to Australia, and broke loose spending a long time supporting a set of islands before it became incorporated into Asia.

“The ancestors of Retinosaurus might have survived for about 50 million years in these islands, which would explain their presence here, while another radiation moved to North America,” the paper notes.

Although the tail and rear legs are missing from the amber, it offers many things other fossils do not, such as its scales and left eyelid. This eyelid represents the most notable difference from the Xantusiidae, whose eyelids are fused into a transparent scale, like that of snakes.

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Despite this difference, it is thought Retinosaurus had a similar lifestyle to night lizards, spending most of its life in rock crevices and gaps in logs.

A reconstruction of Retinosaurus in its natural environment. Don't touch the tree sap little lizard! Image Credit: Stephanie Abramowicz CC BY 4.0

The same piece of amber also includes several beetles, because it is hard to hang out in a rainforest and not have some beetles present.

Now we just need enough amber to trap a whole Brontosaurus. Oh and some pretty big developments in DNA reconstruction. 


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