The timeline of therizinosaur research is a chronological listing of events in the history of paleontology focused on therizinosaurs. They were unusually long-necked, pot-bellied, and large-clawed herbivorous theropods most closely related to birds. The early history of therizinosaur research occurred in three phases. The first phase was the discovery of scanty and puzzling fossils in Asia by the Central Asiatic Expeditions of the 1920s and Soviet-backed research in the 1950s. This phase resulted in the discovery of the Therizinosaurus cheloniformis type specimen. Soviet paleontologist Evgeny Maleev interpreted these unusual remains as belonging to some kind of gigantic turtle. The second major phase of therizinosaur research followed the discovery of better preserved remains in the 1970s by collaborative research between the Soviets and Mongolians. These finds revealed the true nature of therizinosaurs as bizarre dinosaurs. However, the exact nature and classification of therizinosaurs within Dinosauria was controversial as was their paleobiology. When Rozhdestventsky first reinterpreted therizinosaurs as dinosaurs he argued that they were unusual theropods that may have used their clawed arms to break open termite mounds or collect fruit. Osmolska and Roniewicz also considered therizinosaurs to be theropods. In 1979, Altangerel Perle named the new species Segnosaurus galbinensis, which although he recognized was an unusual theropod, he did not recognize as a therizinosaur. Consequently, he named the new family Segnosauridae and, in 1980, Segnosauria. Two years later, Perle recognized commonalities between Therizinosaurus and segnosaurs, reclassifying the former as a member of the latter. From hereout therizinosaur research was considered "segnosaur" research. Perle himself thought that his "segnosaurs" were semi-aquatic fish-eaters. However, in the early 1990s, researchers like Rinchen Barsbold and Teresa Maryańska cast doubt on the connection between therizinosaurs and segnosaurs altogether. Nevertheless, the description Alxasaurus elsitaiensis provided more evidence for a close relationship between the therizinosaurs and "segnosaurs" and led to a revision of their classification. The discovery of this and other primitive therizinosaurs in China formed the beginnings of the third major wave of therizinosaur research. That same year Russell and Russell reinterpreted therizinosaurs as herbivorous foragers like mammalian chalicotherium. Other significant finds of the 1990s include therizinosaur eggs with embryos preserved inside and the first known therizinosaur with feathers, Beipiaosaurus, which was described from China in 1999.
20th century
1950s
1954 Evgeny Maleev described the new genus and species Therizinosaurus cheloniformis. from the Nemegt Formation He interpreted it as a gigantic turtle. Maleev also named the family Therizinosauridae to contain this species.
1960s
1964 Zakharov described and named the genus and type ichnospecies Macropodosaurus gravis, which is represented by a series of four-toed footprints.
1970s
1970 Rozhdestventsky first proposed the idea that therizinosaurids were actually theropod dinosaurs. He thought they used their large claws to tear open termite mounds or collect fruit from trees. Osmolska and Roniewicz also interpreted Therizinosaurus as a carnosaur theropod.
1976 Barsbold proposed the Deinocheirosauria and included Therizinosaurus as a member. In another paper during the same year, Barsbold referred a shoulder and forearm found in the same strata as the Therizinosaurus type specimen to that genus because of the resemblance between the specimens claws. He observed that the anatomy of the arm and shoulder remains suggested that it belonged to a theropod dinosaur. Barsbold also remarked on similarities it shared with Deinocheirus, another mysterious dinosaur from the same rock unit.
1979 Dong described the new genus and species Nanshiungosaurus brevispinus based on a vertebral column and pelvis. He interpreted Nanshiungosaurus as a new genus of dwarf sauropods. He also described the new species Chilantaisaurus zheziangensis but interpreted it as a carnosaur. Perle described the new genus and species Segnosaurus galbinensis based on mostly complete limbs and girdles. He erected a new family, the Segnosauridae, for this unusual dinosaur. He tentatively regarded it as a theropod.
1980s
1980 Barsbold and Perle named the Segnosauria and described the new genus and species Erlikosaurus andrewsi. They also described in brief detail an unknown segnosaur. Barsbold and Perle thought segnosaurs were slow, semi-aquatic animals.
1981 Perle redescribed the holotype of Erlikosaurus but this time in more detail and misspelled Erlicosaurus.
1982 Perle reported an unusual partial four-toed hind limb from Hermiin Tsav, Nemegt Formation. Because this partial leg was found not far from where Barsbold reported the shoulder and humerus he referred to Therizinosaurus, Perle thought that his specimen also probably belonged to that taxon. Since this leg was similar to those of segnosaurs, he classified Therizinosaurus as a segnosaur.
1983 Barsbold described the new genus and species Enigmosaurus mongoliensis based on a partial pelvis from the previously unknown segnosaur. Barsbold regarded Enigmosaurus as so unusual that he gave it its own family, the Enigmosauridae.
1984 Paul suggested that segnosaurs shared an evolutionary relationship with prosauropods and ornithischians. He thought this implied that they were probably herbivores.
1986 Gauthier considered segnosaurs to be relatives of sauropodomorphs.
1989 Paul Sereno also followed this new interpretation of segnosaurs. Bryn J. Mader and colleagues re-examined the specimens assigned to Alectrosaurus and concluded that the large humerus and unguals used by Gilmore in 1933 did not come from a tyrannosauroid, but a therizinosaurid.
1990s
1990 Barsbold and Maryanska reinterpreted the theropod Nanshiungosaurus and the carnosaur Chilantaisaurus as segnosaurs. They agreed with Perle that the partial hind limb from Hermiin Tsav he described in 1982 was segnosaurian, but cast doubt with his referral of it to Therizinosaurus, and therefore with his subsequent conclusion that Therizinosaurus was a segnosaur. Barsbold and Maryanska also disagreed with previous researchers who classified Deinocheirus as a segnosaur. David B. Norman considered Therizinosaurus to be a theropod of uncertain classification.
… excerpt ends here. Continue reading the full article.
