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The “Monkeydactyl” also had opposable thumbs

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A new 160-million-year-old arboreal pterosaur species, nicknamed “Monkeydactyl”, represents the oldest record of opposable thumbs.

These big fingers that oppose the other four have long been considered the prerogative of humanity … wrongly. Opposable thumbs are indeed characteristic of primates. They are also found in certain tree frogs or in chameleons. When were these tools developed? Answer: at least 160 million years ago.

The first recording of a real opposable thumb

In the review Current biology, a team of paleontologists details the discovery of a new species of flying reptile described from a specimen recovered from the Tiaojishan Formation in Liaoning, China. Kunpengopterus antipollicatus, its scientific name, was a small member of the large pterosaur family with a wingspan of around 85 centimeters only.

On the other hand, this new species stands out for another reason: at the end of these wings developed an opposable finger. For this reason, researchers bring up the nickname “Monkeydactyl” (or “monkey finger”).

This incredible discovery was made possible thanks to an analysis of its fossil by microcomputed tomography (micro-CT), a scanning technique that uses X-rays to image an object.

The fingers of this pterosaur are tiny and partially sunk into the slab. Thanks to microtomodensitometry, we were able to see through rocks, create digital models and tell how the opposable thumb articulates with the other bones of his fingers.“, Explains Fion Waisum Ma from the University of Birmingham.

The K. antipollicatu fossil found in the Tiaojishan Formation, now in the Beipiao Pterosaur Museum. Credits: Zhou et al., 2021.

An arboreal life

The “Monkeydactyl” thus represents the oldest palmar opposition record of the pollex (opposable thumbs).

The authors believe that the morphology of its forelimbs appeared to be a practical adaptation to arboreal life, useful for grabbing branches during their ascent. This species would thus have carved out a niche different from that of its neighboring pterosaurs Darwinopterus and Wukongopterus who shared the same environment, which probably minimized the competition between these pterosaurs.

opposable thumb pterosaur
Reconstruction of the life of K. antipollicatus. Credit: Chuang Zhao

We know that the pterosaurs, which lived in the Mesozoic, were the first known vertebrates to evolve in powered flight. However, arboreal locomotion has sometimes been considered to have played a role in the origin of the flight of these reptiles. We could thus ask ourselves by extension whether the evolution of the opposable thumb has not contributed to that of motorized flight.


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