Open Paleo

Therizinosaurus

Maleev, 1954 THER-i-ZIN-o-SAWR-us /ˌθɛrəˌzɪnoʊˈsɔːrəs/

From Greek therizein ('to reap' or 'to cut') and sauros ('lizard'), meaning 'scythe lizard', named for its enormous scythe-like claws

72.2–66.0 million years ago Maastrichtian, Late Cretaceous
Late Cretaceous stages

Therizinosaurus is a genus of very large therizinosaurid dinosaurs that lived during the Late Cretaceous period in what is now Asia. It contains a single species, Therizinosaurus cheloniformis, known from the fossiliferous Nemegt Formation. The first remains of Therizinosaurus were found in 1948 by a Mongolian field expedition in the Gobi Desert and later described by Evgeny Maleev in 1954. The genus is only known from a few bones, including gigantic manual unguals (claw bones), from which it gets its name, and additional findings comprising fore and hindlimb elements that were discovered from the 1960s through the 1980s.

Diagnosis

  1. Enormous sickle-like ungual phalanges on forelimbs, 60-65cm in length with grooved surfaces
  2. Massive metacarpal bones with great mobility at distal articulation
  3. Broad, compressed body reaching 3.5-4.5m in length with 3m width
  4. Ribs with T-shaped dorsal section and well-developed intercostal muscle attachment sites
  5. Reduced or nearly absent bony armor unlike typical sea turtles
  6. Powerful forelimbs with enlarged claws adapted for cutting aquatic vegetation

Species

Therizinosaurus cheloniformis Maleev, 1954

Type species

From Ancient Greek 'chelone' meaning 'turtle' and Latin 'formis' meaning 'in the form of', reflecting the original describer Evgeny Maleev's interpretation that the remains belonged to a large turtle-like reptile.

Holotype
PIN 551-483 , Paleontological Institute, Russian Academy of Sciences
Material
Forelimb elements including giant claws
Horizon
Nemegt Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
fifth quarry, Nemegt, Ömnögovi, Mongolia

Notable specimens

  • MPC-D 100/15

    Paleontological Center, Mongolian Academy of Sciences Found 1973 complementary

    Much more complete, larger, articulated specimen from Hermiin Tsav preserving both arms (scapulocoracoids, humeri, ulnae, radius, carpals, metacarpus with complete digit II, ribs and gastralia), greatly extending forelimb anatomy beyond the claw-only holotype and confirming theropod identity.

    Barsbold (1976)

  • MPC-D 100/45

    Paleontological Center, Mongolian Academy of Sciences Found 1973 complementary

    Referred right hindlimb from Hermiin Tsav (fragmented femur, lower tibia, astragalus, calcaneum, tarsal IV, four metatarsals and digits) providing the only known foot anatomy of the genus and documenting its unusual functional tetradactyl, weight-bearing pes.

    Perle (1982)

References

  1. Barsbold, R. (1976). Novyye dannyye o terizinozavre (Therizinosauridae, Theropoda) [New data on Therizinosaurus (Therizinosauridae, Theropoda)]. Paleontology and Biostratigraphy of Mongolia 3: 76-92. Nauka Press. barsbold1976a
  2. Perle, A. (1982). O nakhodke zadney konechnosti Therizinosaurus sp. iz verkhnego mela Mongolii [On a new finding of the hindlimb of Therizinosaurus sp. from the Late Cretaceous of Mongolia]. Problems in Mongolian Geology 5: 94-98. perle1982b
  3. Maleev, E. A. (1954). Noviy cherepachoobrazhniy yashcher v Mongolii [New tortoise-like saurian from Mongolia]. Priroda 1954(3): 106-108. maleev1954a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026c