It is a key element of manual dexterity: humans and some highly developed animal species can place their thumbs opposite the other fingers of the hand. Paleontologists have now discovered the oldest example of this so-called vulnerability in a pterosaur from the Jurassic period. With the opposing thumbs of the claws on his wings, he could possibly hold prey well and climb skillfully in the branches. Because the characteristics of the animal suggest a way of life in the trees, explain the scientists. They gave the unusual pterosaur the nickname “monkey fingers”.
The dexterity of the hands is a secret of the success of our species: In humans, the mobility of the thumbs that is responsible for this is particularly highly developed and enables, among other things, the precise grip of tweezers in conjunction with the index finger. In other primates, too, the ability to be exposed is widespread and examples in various forms are also known from some other animal groups. In the case of reptiles, however, there is only one group with real opposing thumbs: the evolutionarily relatively young chameleons have produced this adaptation for their climbing lifestyle. But now an international team of paleontologists is reporting on another example from the deeper evolutionary history of vertebrates.
Oldest known example
It is a hitherto unknown representative of the pterosaurs, the remains of which were discovered in the Tiaojishan Formation in northeast China. The extremely well-preserved fossil was dated to an age of around 160 million years. It is a relatively small pterosaur with a wingspan of about 85 centimeters. The paleontologists assigned it to the family of Darwinoptera pterosaurs, of which, according to earlier finds, apparently different representatives whizzed through the air at the site in the Jurassic period. In order to uncover details of the physical features of the fossil, the researchers examined the fossil with the help of micro-computed tomography, which can provide non-destructive insights into hidden areas of a find.
As the paleontologists report, it became apparent that the pterosaur had claws on its wing fore limbs, which were characterized by an opposite pollex (thumb). This was a previously unknown feature in pterosaurs. “The little fingers were partly embedded in the stone slab. But thanks to the micro-CT scan, we were able to see through the rock, create digital images and finally model how the opposite thumb interacted with the other finger bones, ”says co-author Waisum Ma of the University of Birmingham.
In this way, the researchers were able to make it clear that the claws with the specially positionable thumbs have given these pterosaurs a good ability to grasp. As they explain, the finding is the earliest evidence of a real opposing thumb in evolutionary history. The researchers also made this clear in the scientific name they gave the pterosaur: Kunpengopterus antipollicatus. The Greek species name “antipollicatus” means “with the opposite thumb”. The paleontologists also use the nickname “Monkeydactyl” – monkey fingers for the unusual pterosaur.
A nimble tree dweller
As they report, it is obvious that the special claw was an adaptation to the way of life in trees. In addition to the flying mode of locomotion, Kunpengopterus antipollicatus could have been able to literally move nimbly in the branches. This indicates a specialization of different pterosaur species in the same ecosystem, the researchers say. “The former forest at the Tiaojishan site was home to at least three genera of Darwinoptera pterosaurs. Our results show that Kunpengopterus antipollicatus occupied a different ecological niche than Darwinopterus and Wukongopterus, which probably minimized competition among these pterosaurs, ”says first author Xuanyu Zhou of the China University of Geosciences in Beijing.
Co-author Rodrigo Pêgas of the Brazilian Federal University of ABC in Sao Bernardo concludes: “Darwinoptera pterosaurs from the Jurassic were named after Darwin because of their transitional anatomy, which shows how evolution has influenced the characteristics of pterosaurs over time named. That is why they were already considered to be particularly interesting representatives of the pterosaurs. And now it has been shown that new Darwinoptera species can apparently continue to cause surprises, ”says the paleontologist.
Source: University of Birmingham, Article: Current Biology, doi: 10.1016 / j.cub.2021.03.030