Dinosaurs A to Z
Therizinosauridae

Therizinosaurus cheloniformis thair-ih-ZEEN-oh-SOR-us

"Scythe lizard"

Therizinosaurus silhouette
You 1.8 m (5.9 ft) tall
Therizinosaurus 10 m (33 ft) long
as long as 6 people standing fingertip to fingertip
silhouette · Cy Marchant (CC-BY) via PhyloPic
Length
10 m (33 ft) — About 10 m long, ~5 tonnes — with claws up to 1 m long.
Period
Late Cretaceous (72–68 Mya)
Place
Asia · Mongolia
Food
Herbivore — Leaves and high branches — used the long arms and claws like a giant tree-leaf rake.
Clade
Therizinosauridae Dinosauria Saurischia Theropoda Coelurosauria Pot-bellied theropods with giant claws — secondarily plant-eating.

The "scythe lizard" wielded the longest hand claws of any animal that ever walked.

Therizinosaurus reconstruction by PaleoNeolitic
Reconstruction · PaleoNeolitic (CC-BY)

Therizinosaurus was a meat-eater that gave up meat. Its ancestors were sharp-toothed coelurosaurs, but Therizinosaurus evolved a wide gut, a small head, and meter-long claws that it used to pull branches down to its mouth. It looked like nothing else in the dinosaur world — part giant sloth, part ground bird, part oversized turkey with kitchen knives.

More about Therizinosaurus

Discovery

Named by Evgeny Maleev · 1954 · the Nemegt Formation of the Gobi Desert, southwestern Mongolia

A Mongolian expedition organized by the USSR Academy of Sciences found three partial hand claws in 1948 at a subdivision of the Nemegt locality called Quarry V, near the skeleton of a large theropod. The Russian paleontologist Evgeny Maleev described them in 1954 and used them to name the new genus and species.

The name Therizinosaurus comes from Greek, combining a word meaning "scythe, reap or cut" with one meaning "lizard," a reference to its enormous hand claws. The species name cheloniformis joins the Greek for "turtle" with the Latin "formis," because the first remains were thought to belong to a turtle-like reptile.

Evgeny Maleev. A Russian paleontologist who described and named Therizinosaurus in 1954, originally classifying it as a giant turtle-like reptile and coining a family of its own for it, Therizinosauridae.

Why did it take so long to figure out what Therizinosaurus actually was?
The genus is known from only a few bones, so early researchers lacked the complete skeletons needed to place it. After Maleev's 1954 turtle interpretation, it was reassigned over the decades to theropods, sauropodomorphs, and even transitional ornithischians. The taxonomic picture only sharpened as more complete relatives like Segnosaurus and Erlikosaurus were discovered.
Was Therizinosaurus feathered?
The text describes Therizinosaurus as likely having sparse feathering, inferred from its more completely known relatives rather than from direct evidence on its own incomplete remains. Many of its physical traits, including the feathering, are reconstructed by comparison to closer kin.

What we know

  • Claws up to 1 m long — the largest of any known animal.
  • Wide-bellied build with a small head and a long neck, like other plant-eating theropods.
  • Coelurosaur — closely related to oviraptors and tyrannosaurs.
  • Lived alongside Tarbosaurus in the Nemegt Formation of Mongolia.

What we guess

  • What the giant claws were for — leaves, defense, mating display, or all three.
  • Feathered body covering — almost certain given its relatives, but no preserved feathers yet.
  • Whether it could rear up on two legs to reach high branches like a giant ground sloth.