Therizinosauria
Therizinosauria is a clade of secondarily herbivorous maniraptoran theropods, once known as segnosaurs, whose fossils come mainly from Cretaceous rocks of Asia and North America, with fragmentary remains hinting at a history reaching back into the Jurassic of Asia and Europe. Its members range from small, lightly built early-diverging forms such as Falcarius and Beipiaosaurus to the giant Therizinosaurus, which grew around 10 meters long and ranks among the largest known theropods. They combined a puzzling mix of traits: long necks, wide barrel-shaped torsos, and four-toed walking feet reminiscent of basal sauropodomorphs, together with backward-pointing, partly fused hip bones that once suggested a link to the bird-hipped ornithischians. Their most striking feature is the enormous claws on their hands, reaching roughly a meter in Therizinosaurus, which they likely used to grasp and shear leafy branches much as later mammals like ground sloths and giant pandas did. Skin impressions show that at least some members bore a coat of down-like feathers along with longer, quill-like structures that may have served in display.
Under dispute
The position of Therizinosauria within Maniraptoriformes is unsettled. Historically therizinosaurs were recovered within Maniraptora, often close to Oviraptorosauria (Zanno, 2010), a pairing Hartman and colleagues (2019) find much less likely. More recent analyses disagree: Hartman and colleagues (2019) recover Therizinosauria and Alvarezsauroidea as the first-branching maniraptorans, whereas Cau (2024) recovers Therizinosauria as the sister group of Ornithomimosauria and outside Maniraptora. Hartman and colleagues (2019) find the base of Maniraptoriformes less well supported than consensus suggests, with alternative arrangements only a few steps longer.
Diagnosis
- Distal reduction in dentary tooth size combined with a high tooth count set in interdental plates behind a downturned, buccally emarginated dentary
- Small lanceolate crowns with coarse denticles and a constricted base
- Enlarged, mediolaterally compressed manual unguals
- Opisthopubic pelvis with a broadly everted preacetabular process of the ilium
- Reduced, robust pes trending toward a functionally weight-bearing first digit
Clades within Therizinosauria
- Therizinosauroidea 14 genera
Genera placed directly in Therizinosauria
- Falcarius Barremian (125.8–121.4 Ma)United States
- Jianchangosaurus Barremian (125.8–121.4 Ma)Chinaunder dispute
- Kayrasaurus Barremian (125.8–121.4 Ma)China
- Martharaptor Barremian (125.8–121.4 Ma)United Statesunder dispute
References
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Russell, D. A. (1997). Therizinosauria. Encyclopedia of Dinosaurs (Currie, P. J.; Padian, K., eds.) 729-730. Academic Press.
Defined and diagnosed Therizinosauria in an encyclopedia entry, as six named genera and all taxa closer to them; Zanno (2010) credits the name to this paper.
russell1997a -
Zanno, L. E. (2010). A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology 8(4): 503-543. doi:10.1080/14772019.2010.488045
Redefined Therizinosauria as the most inclusive clade containing Therizinosaurus cheloniformis but not Tyrannosaurus, Ornithomimus, Mononykus, Oviraptor or Troodon.
zanno2010a -
Cau, A. (2024). A Unified Framework for Predatory Dinosaur Macroevolution. Bollettino della Società Paleontologica Italiana 63(1): 1-19. doi:10.4435/BSPI.2024.08
Recovered Therizinosauria as the sister group of Ornithomimosauria and outside Maniraptora.
cau2024a -
Hartman, S.; Mortimer, M.; Wahl, W. R.; Lomax, D. R.; Lippincott, J.; Lovelace, D. M. (2019). A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ 7: e7247. PeerJ. doi:10.7717/peerj.7247
Recovered Therizinosauria and Alvarezsauroidea as first-branching maniraptorans.
hartman2019a