Alvarezsaurs Claws When Digging Dirt

Unlocking the Secrets of Dinosaur Claws: Study Reveals Surprising Functions

Alvarezsaurs Claws When Digging Dirt

Alvarezsaurs claws when digging dirt. Credit: Shuyang Zhou for the 3D modeling and functional scenario restoration

The claws of dinosaurs had many functions, but a team from the University of Bristol and the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) in Beijing has now demonstrated that some predatory dinosaurs used their claws for digging or even for display purposes.

The study, which centered on two groups of theropod dinosaurs – the alvarezsaurs and therizinosaurs – aimed to uncover the mystery surrounding their peculiar claws. The findings revealed that the rock-pick-like claws of the alvarezsaurs were utilized for digging, while their close relatives, the giant therizinosaurs, used their overgrown, meter-long, sickle-shaped claws for display purposes.

The new work is led by Zichuan Qin, a Ph.D. student at the University of Bristol and the IVPP. He developed a new, computational approach in biomechanics to identify functions based on detailed comparison with living animals. First, the claws were modeled in three dimensions from CT scans, then modeled for stress and strain using engineering methods, and finally matched to functions of pulling, piercing, and digging by comparison with modern animals whose claw functions are known.

Therizinosaurs Claws Hooking and Pulling Trees

Therizinosaurs claws hooking and pulling trees. Credit: Shuyang Zhou for the 3D modeling and functional scenario restoration

“Alvarezsaurs and therizinosaurs are definitely the strangest cousins among dinosaurs,” said Professor Michael Benton, one of Zichuan’s supervisors. “Alvarezsaurs were the tiniest dinosaurs ever, the size of chickens, with stubby forelimbs and robust single claws, but their closest relative, the therizinosaurs, evolved in the exact opposite path.”

Therizinosaurus is famous for its sickle-like claws, each as long as a samurai sword: Edward Scissor-hands on speed. We all saw Therizinosaurus in ‘Jurassic World’ hitting deer and killing the giant predator Giganotosaurus. However, this is unlikely. These long, narrow claws were too weak for combat.” said Dr. Chun-Chi Liao, an expert on therizinosaurs from IVPP who co-authored this study. “Our engineering simulation shows that these claws could not withstand much stress.”

“Not all therizinosaur hand claws were so useless in combat, but most other related species could use their claws as powerful hooking tools when feeding on leaves from the trees,” Dr. Chun-Chi Liao added, “so, we conclude that the largest claws of any animal ever were actually useless in mechanical function, and so must have evolved under sexual selection to be used in display. The adult Therizinosaurus I guess could wave the claws at a competitor and effectively say, ‘look at me, back off’ or wave them around in some way like a peacock can use its tail in display to attract females for mating.”

Dinosaur Claws Used for Digging and Display Graphical Abstract

Key taxa and work pipeline use in this paper. Silhouettes show the large and elongated forelimb of the late-branching therizinosaurian Therizinosaurus (a) and the overall body shape and highlighted forelimb of the late-branching alvarezsauroid Mononykus (b), scaled against an adult human (height ~1.8 m). The work pipeline demonstrated by an ungual model from the Jurassic alvarezsauroid Haplocheirus, includes processes of 3D model reconstruction (c); model smoothing, measurement, and morphological analysis (d); finite-element analysis, ‘intervals’ method and functional-space analysis (e); and total evidence functional assessment (f). Credit: Zichuan Qin

“Our previous work has shown that alvarezsaurs evolved to become the tiniest dinosaurs by the end of the Cretaceous, and these dinosaurian midgets were using their punchy little claws for digging into ant hills and termite mounds. They were ant-eaters,” said Zichuan Qin.

“Our study shows that the early alvarezsaurs, like Haplocheirus from the Jurassic, had multifunctional hands, but they were not good at digging. Their much smaller descendants had the efficient digging hands so they could feast on the Late Cretaceous termites,” added Zichuan Qin.

“Science and technology cannot bring dinosaurs back to life, but advanced computing and engineering techniques can show us how extinct animals lived,” said Professor Emily Rayfield, one of Zichuan’s supervisors, and an expert of dinosaur biomechanics. “Especially for extinct animals like alvarezsaurs and therizinosaurs, they are so bizarre that we even can’t find any living animals like them. Luckily, advanced technology can help us to simulate, on a computer, the functioning of extinct animals using fundamental engineering and biomechanical principles. This study shows very well how selection for function can lead to the emergence of specific, sometimes very bizarre, forms.”

Reference: “Functional space analyses reveal the function and evolution of the most bizarre theropod manual unguals” by Zichuan Qin, Chun-Chi Liao, Michael J. Benton and Emily J. Rayfield, 16 February 2023, Communications Biology.
DOI: 10.1038/s42003-023-04552-4

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