Meet the "monkeydactyl": a recently-discovered arboreal species of pterosaur, dated at 160 million years old, with the oldest true opposed thumb known - a feature previously undiscovered in these flying reptiles.

An international collaboration of researchers from the UK, Denmark, Japan, Brazil, and China discovered the new species in the Tiajishan Formation in Liaoning, northeastern China. The newly discovered "monkeydactyl" is formally designated as the Jurassic pterosaur Kunpengopterus antipollicatus, with its species name taken from the Greek word for "having opposite thumbs" - its most significant feature.

Researchers report their findings in the journal Science Daily, in an article titled "New Jurassic flying reptile reveals the oldest opposed thumb."

The complete skeleton of Kunpengopterus sinensis (IVPP V 23674)
(Photo: Xin Cheng, Shunxing Jiang, Xiaolin Wang​, Alexander W. A. Kellner via Wikimedia Commons)
(A) Photo and (B) line drawing with missing portions of the skeleton were preserved as an impression in dark grey. Scale bars: 50 mm.

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Oldest Opposed Thumbs on Record

In the report, the K. antipollicatus is a small-bodied darwinopteran pterosaur - a genus of flying reptiles found mostly in China and has features from both long-tailed and short-tailed pterosaurs. It has an estimated wingspan of 85 centimeters or about 33 and a half inches. Its most important feature was an opposed "pollex" or thumb on both hands.

True opposed thumbs are mostly present in mammals, especially primates, as well as in some species of tree frogs.

However, this feature is relatively rare among currently existing reptiles, with opposed thumbs only found in chameleons. The new discovery supports the notion of darwinopteran pterosaurs such as the newly-found K. antipollicatus also developed opposed thumbs.

The Tiajishan Formation remains were scanned by researchers using micro-computed tomography (micro-CT), which uses X-ray to develop images of a subject.

Additional studies revealed that K. antipollicatus was most likely an arboreal being, meaning it lived mostly on trees. Its forelimb morphology and musculature strongly suggest the use of its hand for grasping and gripping, skills used for moving up and across trees.

To further test the theory of the "monkeydactyl" being an arboreal creature, researchers tested its remains with samples from other species of pterosaurs. They used a set of anatomical characters often related to adaptations toward arboreal lifestyles. Researchers found that other pterosaurs - despite coming from the same ecosystem - do not fit the criteria for arboreal creatures; K. antipollicatus did.

The findings suggest that niche-partitioning - where natural selection drives otherwise competing species toward different "niches" for increased survival chances - was responsible among the flying reptiles. Additionally, it provides the first quantitative evidence about the existence of arboreal darwinopteran pterosaurs.

Monkeydactyl Embedded in Stone

Fion Waisum Ma, co-author of the study and a Ph.D. researcher from the University of Birmingham explains that the fingers of this "monkeydactyl" are "tiny and partly embedded in the slab." They were able to accurately image these features through micro-CT, seeing through the rocks, create digital models from the remains, and even demonstrate how the opposed thumb supposedly articulates with its other fingers.

"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," Ma added in a University of Birmingham release


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