page_title: Therizinosaurus
section_title: Classification
hierarchical_section_title: Therizinosaurus / Classification
caption_attribution_description: English: Beipiaosaurus inexpectus feathers on display at the Paleozoological Museum of China.
context_page_description: Therizinosaurus is a genus of very large therizinosaurid dinosaurs that lived in Asia during the Late Cretaceous period in what is now the Nemegt Formation around 70 million years ago. The first remains of Therizinosaurus were found in 1948 by a Mongolian field expedition at the Gobi Desert. Fossils of this species were first described by Evgeny Maleev in 1954 and originally thought to belong to a turtle-like reptile. It is known only from a few bones, including gigantic hand claws, from which it gets its name. Additional findings compromising forelimb and hindlimb elements have been discovered during the 1960s-1980s.
  Therizinosaurus comprises the single species T. cheloniformis, which could grow up from 9 to 10 m long and weigh possibly over 5 t. They had the longest known claws of any land animal, reaching up to 1 m in length. Unlike other therizinosaurs, the claws were very stiff and elongated. But like other members, they would have been slow, long-necked/high browser herbivores equipped with a keratinous beak and wide torsos. The feet were equipped with four weight-bearing toes, resembling a little bit the unrelated sauropodomorphs.
context_section_description: The affinities and relationships of Therizinosaurus and kin were problematic in the early years of research. In 1954, Therizinosaurus were considered to have been giant marine turtles and the genus was assigned by Maleev to a separate Therizinosauridae given how enigmatic the type specimen was. The fossils remained with uncertainty among the scientific community, however, in 1970 Rozhdestvensky was one of the first paleontologists suggesting the idea that Therizinosaurus were actually theropod dinosaurs instead of some turtles. He considered that the large claws were used for a herbivorous life-style and open termites mounds. Also, the supposed ribs of the holotype were likely from a different dinosaur, possibly some sauropodomorph. With the discovery and description of Segnosaurus, in 1979 Perle named a new family of dinosaurs, the Segnosauridae. He tentatively placed the family as theropod dinosaurs given the similarities of the mandible and dentition to other members. A year later, the new genus Erlikosaurus was named by Barsbold and Perle in 1980. They named a new infraorder called the Segnosauria, composed by Erlikosaurus and Segnosaurus. They also noted that while aberrant and having ornithischian-like pelves, segnosaurs featured similar traits to other theropods With the discovery of the referred hindlimb to Therizinosaurus in 1982 by Perle, he concluded that Segnosaurus were very similar to the later based on the pes morphology and they possibly belonged to a single, if not the same group. In 1983, Barsbold named a new genus of segnosaur Enigmosaurus. With this discovery, he analysed the pelvis of this new genus and pointed out that segnosaurids were so different from other theropods that they could be outside the group or represent a different lineage of theropod dinosaurs. Later on the same year, he intensified the exclusion of segnosaurs from being theropods by noting that their pelves resembled those of sauropod dinosaurs.
  Consequently, the assignment of segnosaurs started to shift towards sauropodomorphs. In 1984, Paul claimed that segnosaurs rather than being aberrant theropods were indeed, sauropodomorphs which successfully managed to remain into the Cretaceous period. He based this idea on anatomical traits such as the skull and similar pes configuration. He maintained his position in 1988 by placing the Segnosauria into the now obsolete Phytodinosauria, in addition, he was one of the first in suggest a segnosaur assignment for the long forgotten Therizinosaurus. Other prominent paleontologists like Gauthier or Sereno supported this vision. However, with the unexpected discovery and description of Alxasaurus in 1993, the widely accepted, sauropodomorph affinities of segnosaurs were highly questioned by Rusell and Dong. This new genus was far more complete than any other segnosaur and multiple anatomical features indicated that is was a member of the group and related to Therizinosaurus. With this, they identified the Therizinosauridae along with the Segnosauridae to be same group, the former name having historic priority. Due to some primitive characters present in Alxasaurus they coined a new taxonomic rank, the Therizinosauroidea, containing this new taxon and the Therizinosauridae. All of this new information provided new data on the affinities of the new-named "therizinosaurs"; they concluded that these animals were actual theropods, although uncertainties were still present. In 1994, Clark and colleagues redescribed the very complete skull of Erlikosaurus and even more theropod traits were found this time. They also validated the synonymy of the Segnosauridae with Therizinosaurida and classified therizinosaurs as maniraptoran dinosaurs. Nevertheless, against every opposition, a small and feathered therizinosauroid was described in 1999 by Xu and colleagues, the new genus Beipiaosaurus. It definitely confirmed the placement of therizinosaurs among theropods and also their taxonomic place on the Coelurosauria. This discovery also indicated that feathers were highly distributed among theropod dinosaurs.
caption: Feather impressions from the holotype of Beipiaosaurus
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