Avimimus portentosus (Kurzanov 1981, Dyke 1998, Tsuihiji et al 2017, MPC-D 100/125, Late Cretaceous, 1.5m long) is widely considered an aberrant oviraptorosaur, but here nests basal to therizinosaurs, as a late-surviving sister to oviraptorosaurs. This toothless taxon has a very short metatarsal 3 that does not reach halfway up the rest of the metatarsus. The rostrum is short, which rotates the naris vertically. The eyes were large. The unpreserved posterior mandible must have been strut-like and fragile because the large mandibular fenestra starts far forward behind the very short dentary. These traits suggest Avimimus is the product of phylogenetic miniaturization stemming from a previously unrecognized and undiscovered branch of Jurassic therizinosaurs.

Beipiaosaurus inexpectus (Xu, Tang and Wang 1999; Aptian, Early Cretaceous; 2.2m in length; IVPP V11559, STM 31-1) was derived from the large Compsognathus ONJ79 specimen and basal to the other therizinosaurids, all herbivores.

Falcarius utahensis (Kirkland et al. 2005, 4m, Barremian, Early Cretaceous) is a basal therizionosaur theropod. The holotype skeleton is supplemented by several paratypes found in a bone bed. With a limited taxon list, Falcarius currently nests with the tiny Late Cretaceous Rahonoavis, but that may change with additional taxa. Their clade nests between the Microraptor/Tyrannosaurus clade and the Juravenator/Khaan clade.

The cervicals were elongated. The herbivorous teeth were small. the torso and pelvis were wider to accommodate a larger gut.

Jianchangosaurus yixianensis (Pu et al. 2013; 41HIII-0308A, Early Cretaceous, 2m in length) was originally and here nested as a basal therizinosaur. It is considered a juvenile based on unfused neural spines. Note the closely packed teeth. Feather impressions are included.

Rahonavis (orignally Rahona ostromi - Forster et al. 1998, Late Cretaceous, 70mya, UA 8656, 70 cm) was originally considered a bird-like theropod. Here it nests with Jianchangosaurus among the therizinosaurids.

The partial skeleton was much smaller than sister taxa. The pubis was ventrally oriented and the radius + ulna were very long. The tail was comparatively short with few vertebrae.

Dyke T 1998. Reduced cladistic consensus methods and the avian affinities of Protoavis and Avimimus. Archaeopteryx. 16: 123–129.

Forster CA, Sampson SD, Chiappe LM, Krause DW 1998. The Theropod Ancestry of Birds: New Evidence from the Late Cretaceous of Madagascar. Science 279 (5358): 1915–1919.

Forster CA, O’Connor PM, Chiappe LM and Turner AH 2020. The osteology of the Late Cretaceous paravian Rahonavis ostromi from Madagascar. Palaeontologia Electronica, 23(2):a31. https://palaeo-electronica.org/content/pdfs/793.pdf

Kirkland JI, Zanno LE, Sampson, SD, Clark J M and DeBlieux DD 2005. A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah. Nature 435: 84-87

Kurzanov SM 1981. An unusual theropod from the Upper Cretaceous of Mongolia Iskopayemyye pozvonochnyye Mongolii (Fossil Vertebrates of Mongolia). Trudy Sovmestnay Sovetsko-Mongolskay Paleontologiyeskay Ekspeditsiy (Joint Soviet-Mongolian Paleontological Expedition), 15: 39-49. Nauka Moscow.

Pu H-Y, Kobayashi Y, Lu J-C, Xu L, Wu Y-H, Chang HL Zhang J-M and Jia S-H 2013. An Unusual Basal Therizinosaur Dinosaur with an Ornithischian Dental Arrangement from Northeastern China. PLoS ONE 8(5): e63423. doi:10.1371/journal.pone.0063423

Tsuihiji T, Witmer L et al (5 co-authors) 2017. New information on the cranial morphology of Avimimus (Theropoda: Oviraptorosauria). Journal of Vertebrate Paleontology 37: e1347177.

Xu X, Tang Z-L, Wang X-L 1999. A therizinosauroid dinosaur with integumentary structures from China. Nature. 399 (6734): 350–354. doi:10.1038/20670

wiki/Beipiaosaurus
wiki/Falcarius
wiki/Jianchangosaurus
wiki/Rahonavis
wiki/Avimimus