Сайхания: Көлденең қаңқалы динозаврлар туысы

Extinct genus of dinosaurs

Saichania (Mongolian meaning "beautiful one") is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia and China. The first fossils of Saichania were found in the early 1970s in Mongolia. In 1977 the type species Saichania chulsanensis was named. The description of this species has been based on limited fossil material; especially the rear of the animal is not well known. Saichania was more robustly built than other members of the Ankylosauridae, measuring in length and in body mass. Neck vertebrae, shoulder girdle, ribs and breast bones were fused or firmly connected. Its body was flat and low slung, standing on four short legs. The forelimbs were very powerful. The head was protected by bulbous armour tiles. It could defend itself against predators like Tarbosaurus with a tail club. On the torso keeled osteoderms were present. Saichania bit off plants in its desert habitat with a horny beak and processed them in its wide hindgut.

In 1970 and 1971 a Polish Mongolian expedition found ankylosaurian fossils in the Gobi Desert near Chulsan, or Khulsan. The type species Saichania chulsanensis was named and described by the Polish palaeontologist Teresa Maryańska in 1977, along with the related species Tarchia kielanae. The generic name originates from the Mongolian сайхан (saikhan), meaning "beautiful", referring to the pristine state of preservation of the type specimen. The specific name refers to the provenance near Chulsa. The holotype of Saichania chulsanensis, specimen GI SPS 100/151, was found in a layer of the Barun Goyot Formation, dating from the late Campanian, about seventy three million years old. It consists of a skull and the anterior part of the postcranial skeleton: seven neck vertebrae, ten back vertebrae, the left shoulder girdle, the left forelimb, the two cervical halfrings and extensive armour in life position. The holotype is largely articulated. Referred specimens include ZPAL MgD I/114 consisting of an undescribed fragmentary skull roof and associated armour, and an undescribed, almost complete skeleton with skull, specimen PIN 3142/251. Later, also the juvenile specimen MPC D 100/1305 was referred and extensively described in 2011, seeming for the first time to provide complete information on the postcranial skeleton. However, in 2014 Victoria Megan Arbour concluded that the describers had been misled by the skeleton having been completed with a skull cast of GI SPS 100/151, and that the remainder of the fossil belonged to some other ankylosaur, possibly Pinacosaurus. On the other hand, Arbour added to the number of possible Saichania specimens by referring PIN 3142/250, a skull previously seen as a Tarchia exemplar. This would imply that Saichania, formerly thought to occur solely in the Barun Goyot Formation at Khulsan, is also known from the Nemegt Formation at Khermeen Tsav. Saichania would then be the only ankylosaur definitely known from the Nemegt, its occurrence thus spanning the time of the Campanian–Maastrichtian transition, and early Maastrichtian (Nemegtian) period. Arbour also considered the Chinese taxa Tianzhenosaurus youngi Pang & Cheng 1998 and Shanxia tianzhenensis Barrett, You, Upchurch & Burton 1998 to be junior synonyms of Saichania. The referral of PIN 3142/250 to Saichania was contested by Penkalski & Tumanova who considered this specimen to be referable to a new species of Tarchia, T. teresae.

Saichania was a medium sized ankylosaur, measuring in length and in body mass. The teeth were small and leaf shaped. There are twenty two of them in each maxilla, seventeen in the right and sixteen in the left lower jaw of the holotype. On the rear skull, the oval occipital condyle is obliquely pointing to below, indicating that the entire head was appending. A large hyoid bone apparatus was found, in 1977 the most complete discovered for any dinosaur. It is V shaped with the central parts representing the basihyal and basibranchial, and the branches being the ceratobranchialia. The results of an earlier analysis by Arbour & Currie (2015) is reproduced below.

Saichania lived in a desert habitat, with sand dunes interspersed with oases. Other dinosaurs present in the Barun goyot included Lamaceratops, Bagaceratops and Tylocephale; large theropods have not been found yet. In the later Nemegt the gigantic predator Tarbosaurus was present. Arbour pointed out that Saichania, Tarchia and Zaraapelta shared the same habitat. She assumed that this relative ankylosaurian abundance in species had been caused by them being the main herbivores in the area, enough crop thus being available to feed three populations, although their relative niches were unclear. The differences in head ornamentation would then have served species recognition. She saw no indications of sexual dimorphism.