Dinosaur ‘reaper’ with massive claws found in Japan
Millions of years ago, a bipedal dinosaur with knives for fingers stalked the shores of the Asian continent. But those Edward Scissorhands-like weapons were used for slashing vegetation rather than eviscerating animal prey. The dinosaur belonged to a group known as therizinosaurs – bipedal and primarily herbivorous three-toed dinosaurs that lived during the Cretaceous period about 145 million to 66 million years ago. Recently, researchers from Japan and the US described the youngest therizinosaur fossil ever found in Japan; that fossil also happens to be the first to be found in Asia in marine sediments.
This fossil represents a newly described species, which the researchers named Paralitherizinosaurus japonicus. The genus, which was already known to science, means ‘reptile by the sea’ in Greek and Latin; the species name honours Japan, where the specimen was unearthed. The hook-shaped fossil, which includes a partial vertebra and a partial wrist and forefoot, was discovered by a
different team of researchers in 2008. Since then, it has been stored in the collections at the Nakagawa Museum of Natural History in Hokkaidō, Japan.
Japanese scientists found the specimen in Nakagawa, a district in Hokkaidō located on the northernmost of Japan’s main islands, a locale known for its rich fossil deposits. The fossil was encased in a concretion – a hardened mineral deposit – and at the time of its discovery palaeontologists said it “was believed to belong to a therizinosaur,” though due to a lack of comparative data at the time, the original researchers were unable to draw any definitive conclusions. However, new data from many other fossils that were discovered and described in the years since has helped with classifying the fossil based on the shape of the forefoot claw. This prompted a new team of palaeontologists to revisit the specimen to get some definitive answers.
Based on their analysis, researchers concluded that the fossil, which measures just under ten centimetres in length, belonged to a therizinosaur that lived approximately 80 to 82 million years ago.
The fossilised foot bone once held the dinosaur’s swordlike claw, which it used for combing through vegetation for plants to eat. Because researchers suspect that the animal used its claws for a specific purpose, they determined that the specimen was a derived therizinosaur – one that evolved later in the group’s lineage – rather than a basal, or early therizinosaur, with claws that were “generalised and not for specific use”.
“[This dinosaur] used its claws as foraging tools, rather than tools of aggression, to draw shrubs and trees closer to its mouth to eat,” said palaeontologist Anthony Fiorillo, a research professor at Southern Methodist University in Texas. “We believe it died on land and was washed out to sea.” Based on this specimen, it’s impossible to know for sure how large the therizinosaur was. What scientists can say with certainty is that the dinosaur was sizable, possibly as large as a hadrosaur, or duck-billed dinosaur, which could grow to be nine metres long and weigh up to 2.7 tonnes.