Monkeydactyl: the new pterosaur with the oldest opposable thumbs

It flew through the skies on metre-wide wings, but this newly discovered, 160-million-year-old pterosaur shared an unexpected evolutionary quirk with primates: opposable thumbs.

Dubbed ‘Monkeydactyl’, the pterosaur Kunpengopterus antipollicatus, described in the journal Current Biology by an international team of researchers, was found in the Tiaojishan Formation of Liaoning, north-eastern China. The Tiaojishan Formation is a fossil bed that spans 2,420 metres of pyroclastic deposits and sediment, known for its richly preserved fossils from the late Jurassic.

Artist's reconstruction of the monkeydactyl pterosaur with opposable thumbs.
Life reconstruction of K. antipollicatus. The opposed pollex could have been used for grasping food items, as well as clinging and hanging to trees. Image credit: Chuang Zhao.

Monkeydactyl had an estimated wingspan of 85cm and an opposed thumb on each hand – an anatomical quirk found most prevalently in mammals and tree frogs, but only rarely in reptiles, like the chameleon. Importantly, this fossilised thumb is the oldest currently known in Earth’s history, and shows that the winged creature lived an arboreal life.

The team scanned Monkeydactyl using micro-computed tomography (micro-CT) to X-ray the fossil, and analyse the morphology and musculature of its grasping forelimb.

Fion Waisum Ma, co-author of the study and PhD researcher at the University of Birmingham, says: “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.”

Photo and digital model of monkeydactyl left hand.
Photo and digital model of the left hand of K. antipollicatus, showing the opposed thumb. Credit: Zhou et al., 2021.

Other pterosaurs found in the same context were not arboreal, suggesting the area was a complex forest habitat in which closely-related species partitioned off into different niches, and thus avoided competition.

The Monkeydactyl is a type of darwinopteran. This group of fossils from the Jurassic period in Eurasia were named after Darwin because the development of their anatomy over time typifies the way evolution by natural selection alters the body. They’ve also been found with fossilised eggs, revealing useful clues about their reproductive process.

Fossil and line drawing of monkeydactyl.
Fossil of K. antipollicatus, discovered in the Tiaojishan Formation of China. It is housed in the Beipiao Pterosaur Museum of China. Credit: Zhou et al., 2021.

“They’ve always been considered precious fossils for these reasons, and it is impressive that new darwinopteran species continue to surprise us,” says Rodrigo V. Pêgas, co-author from the Federal University of ABC in Sao Bernardo, Brazil.

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