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Triops Longicaudatus Red
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Palaeontology: Duonychus tsogtbaatari – the dinosaur with the scissor hands
You could be forgiven for thinking that Mother Nature had reached wildly into her bag of tricks when designing this dinosaur: A small head is enthroned on a long neck that merges into a round, feathered body. In addition, there are strong arms with only two fingers – on which sickle-shaped claws sit, around 30 centimetres long – and two legs, with which the animal trudged upright along the primeval river courses of present-day Mongolia around 90 to 95 million years ago.
‘Duonychus’ means ’two-clawed’
This peculiar dinosaur goes by the name of Duonychus tsogtbaatari and is one of the most unusual representatives of its species discovered to date. Its skeleton was discovered by chance during construction work for a water pipeline in the Gobi Desert. According to a recent study in the scientific journal iScience, an international research team categorises the new species as belonging to the therizinosaur group – a group of herbivorous dinosaurs that lived in both Asia and North America during the Cretaceous period.
But although Duonychus belongs to the well-known therizinosaur family, it is very different from its relatives. With a length of around three metres and a weight of around 260 kilograms, it has a particular anomaly: its hands do not end in three functional clawed fingers, as is usually the case, but only in two. This is exactly what its name alludes to: ‘Duonychus’ means ‘two-clawed’ in Greek. The huge, curved claws give it a bizarre and fascinating appearance reminiscent of the classic film Edward with the Scissor Hands – it is not for nothing that the group is sometimes referred to as ‘dinosaurs with scissor hands’.
‘Therizinosaurs are already among the strangest dinosaurs,’ palaeontologist Yoshitsugu Kobayashi from Hokkaido University in Japan, who led the study, told Reuters. ‘They are theropods – actually relatives of carnivores – but looked like giant, feathered sloths.’ Duonychus took this peculiarity to the extreme: ‘It had short, two-fingered hands with claw-like weapons like a raptor, but probably used them to pick plants. It’s as if evolution simply wanted to try something completely new – and it worked.’
The find is particularly impressive not only because of its rarity, but also because of its exceptionally well-preserved condition – especially the arms and hands. Although the skull and legs are missing, one of the claws was found complete with its keratin sheath. This is remarkable, as the outer sheath suggests that the actual length of the claw was around 40 per cent longer than that of the bone – an impressive ratio in relation to the body size.
The researchers suspect that the gigantic claws were not only used for defence, but above all helped in the search for food. While other therizinosaurs were partially omnivorous, Duonychus tsogtbaatari appears to have been a pure herbivore. The strongly curved claws and the flexible wrist indicate that it used its claws for grasping – despite the reduced number of fingers. According to the study, it was even able to grasp branches with a diameter of up to ten centimetres.
The missing third finger did not appear to be a disadvantage. On the contrary: the loss of individual fingers is a well-known pattern in the evolution of theropods. A prominent example is Tyrannosaurus rex, whose arms largely lost their function over time. In Duonychus, on the other hand, the two-fingered construction plan is a first among therizinosaurs – a phenomenon whose cause is still unclear. Why a herbivorous grasping specialist lost one of its fingers remains a mystery of evolution for the time being.
