New Jurassic "Monkeydactyl" Is The Earliest Example Of Opposed Thumbs

These thumbs are good for climbing, and that's what they probably did. Image credit: Chuang Zhao

What had two thumbs and was wiggling them with abandon back in the Jurassic? According to a new paper published in the journal Current Biology, the “Monkeydactyl”. This new-to-science flying reptile species was described by an international team of researchers from China, Brazil, UK, Denmark, and Japan from a specimen recovered in the Tiaojishan Formation of Liaoning, China. The discovery of Kunpengopterus antipollicatus, to use its given scientific name, is a pivotal one, representing the earliest known evidence of true opposed thumbs as well as being the first time this feature has been found in a pterosaur.

The researchers on the study state that Monkeydactyl, as it has been dubbed, was lurking in treetops approximately 160 million years ago, likely as an arboreal pterosaur alive in the Jurassic. It’s a small member of the darwinopteran pterosaurs (named after the naturalist for their unique morphology, which informed how evolution shaped pterosaur anatomy over time), whose wingspan is thought to have been around 85 centimeters (33.5 inches). It’s not the breadth of this species that makes them notable, however, as at the end of these wings sat a pretty sophisticated piece of kit for a pterosaur: an opposed thumb. The snazzy appendage inspired Monkeydactyl’s given scientific name, as "antipollicatus" means "opposite thumbed" in ancient Greek. As the earliest record of a true opposed thumb in Earth’s history, it’s a worthy trait to inspire nomenclature and one that’s well-deserving of a thumbs up from all who enjoy them.

“The fingers of ‘Monkeydactyl’ are tiny and partly embedded in the slab. Thanks to micro-CT scanning, we could see through the rocks, create digital models and tell how the opposed thumb articulates with the other finger bones," said Fion Waisum Ma, co-author of the study and PhD researcher at the University of Birmingham, in a statement.

"This is an interesting discovery. It provides the earliest evidence of a true opposed thumb, and it is from a pterosaur, which wasn’t known for having an opposed thumb.”

Opposed pollexes, as thumbs are also known, are mostly seen among mammals like primates, and some tree frogs and even chameleons, though such thumbs are otherwise very rare among extant reptiles. The team was able to confirm that they were indeed looking at an opposed thumb thanks to micro-computed tomography (micro-CT), a scanning technique that uses X-rays to piece together an image of an object, such as a fossil.

Monkeydactyl

Fossil of K. antipollicatus, discovered in the Tiaojishan Formation, now kept at the Beipiao Pterosaur Museum in China. Image credit: Zhou et al., 2021.

The study authors think the Monkeydactyl’s forelimb morphology (gleaned from the micro-CT) suggests the thumb emerged as a handy adaptation for arboreal life, useful for grasping branches as they climbed. They established this hypothesis by comparing the anatomical characteristics of K. antipollicatus against those of other pterosaurs from the same ecosystem. The results indicated that Monkeydactyl carved out a different niche from its pterosaur neighbors, which – if correct – is the first evidence for arboreal darwinopteran pterosaurs.

“Tiaojishan palaeoforest is home to many organisms, including three genera of darwinopteran pterosaurs,” said Xuanyu Zhou from the China University of Geosciences, who led the study. “Our results show that K. antipollicatus has occupied a different niche from Darwinopterus and Wukongopterus, which has likely minimized competition among these pterosaurs.”

If you're a fan of the porgs in Star Wars and pterosaurs breaking the mold, you're gonna love this pterosaur.


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