Opisthocoelicaudia (Posterior cavity tail)
Opisthocoelicaudia (Posterior cavity tail)
Named By : Borsuk-Białynicka - 1977
Diet : Herbivore
Size : Estimated 11 – 13 meters long
Type of Dinosaur : Sauropod
Type Species : O. skarzynskii (type)
Found in : Mongolia - Nemegt Formation
When it Lived : Late Cretaceous, 72-68 million years ago
Opisthocoelicaudia /a,pIsthoUsIlI’ko:di@/ is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. Opisthocoelicaudia skarzynskii is the type species. Polish and Mongolian scientists discovered a well-preserved skull in 1965 that was missing the neck and head. This made Opisthocoelicaudia the most famous Sauropod from the Late Cretaceous. The skeleton’s tooth marks indicate that large carnivorous dinosaurs may have eaten the carcass and possibly taken the missing parts. Only two other, less complete specimens have been found, one of which includes a portion of a shoulder, and one fragmentary tail. Opisthocoelicaudia was a small sauropod measuring approximately 11.4-13m (37-43 feet) in length. It would have had a small head and a long neck, with a trunk shaped like a barrel. The trunk was carried by four columns-like legs. Opisthocoelicaudia is a name that refers to the peculiar, opisthocoel condition in which the anterior tail vertebrae were concave on the posterior side. Researchers also found other skeletal characteristics that suggested Opisthocoelicaudia could reare on its hindlegs.
Maria Magdalena Borsuk Bialynicka, a Polish paleontologist, named and described Opisthocoelicaudia in 1977. It was initially thought that Opisthocoelicaudia might be a new Camarasauridae member, but it is now considered a derived member to the Titanosauria. Although its exact relationship to Titanosauria is disputed, it could have been very close to the North American Alamosaurus. The Nemegt Formation is the source of all Opisthocoelicaudia dinosaur fossils. This rock unit is rich in dinosaur fossils but the only sauropod known from it is Nemegtosaurus. It is known from one skull. Researchers have speculated that Nemegtosaurus may be the same species as Opisthocoelicaudia, despite not knowing the skull of Opisthocoelicaudia. Sauropod footprints found in the Nemegt Formation that include skin impressions can be referred either to Nemegtosaurus, or Opisthocoelicaudia, as these are the only sauropods known from this formation.
The type specimen was found during the joint Polish-Mongolian paleontological expedition of Zofia Jaworowska, a Polish paleontologist. This expedition was the largest among a series of 1963-1971 expeditions. It involved 21 people, who were sometimes supported by additional Mongolian workers. The discovery site is located in Omnogovi Province, southern Mongolia’s Altan Uul region. It exposes about 100 km2 of badlands. Altan Uul’s sediments are part of the Nemegt Formation. This is the youngest of three geological formations in the Nemegt Basin. Opisthocoelicaudia is one of many important dinosaur discoveries made during the 1965 expedition. Other finds were made at various locations, including skeletons from the Tarbosaurus tyrannosaur, as well as type specimens from the Nemegtosaurus and giant ornithomimosaur Deinocheirus.
Ryszard Gradzinski (the expedition’s geologist) discovered a concretion with well-preserved bone fragments that looked like it could be part of a complete skeleton on the fifth day. The next day, excavations revealed that the skeleton was almost complete with the exception of the neck and head. This specimen is still the best-known dinosaur find. Major technical difficulties were encountered in transporting the specimen from rough terrain. The fossilized stones had to be transported 580m by hand on metal sledges made from petrol drums. Many blocks weighed more than a ton because the skeleton was embedded within very hard layers of sandstone. The packing of the skeleton in 35 crates began on July 9 for transport to Dalanzadgad. Together, they weighed approximately 12 tons.
The type specimen belonged an older individual. The unusual taphonomy of this specimen is that it was found on its back. This contrasts with other Nemegt Formation nearly complete dinosaur bones which are usually found on their sides. The specimen was found in a cross-bedded layer of sandstone, which had been deposited by a stream. The majority of the vertebrae found were still connected, making a continuous series consisting of eight dorsal and six sacral vertebrae, as well as thirty-four caudal. Three additional vertebrae were also found, possibly belonging to the area between the neck and back. The remaining parts were slightly shifted from their original anatomical positions. The left limb and the rib bones were located on the right side of a body. Conversely, the right limb was found on the left and the rib bones on the left. The skeleton has been found with bite marks, especially in the pelvis, thigh bone and pelvis, which indicates that the carcass was eaten by predators. The skull and neck are missing which suggests that carnivores may have taken these parts. The remains are complete, indicating that the person had died close to the site. The carcass might have been transported by a flood and then covered with sediment.
Maria Magdalena Borsuk – Bialynicka, a Polish paleontologist, published a detailed description of the skeleton in 1977. She named Opisthocoelicaudia skarzynskii a new genus. Named “posterior cavity tail”, the genus name refers to the peculiar opisthocoel condition in the tail vertebrae. It’s a combination of the Latin cauda, opisthen and koilos. This name is in honor of Wojciech Skarzynski, who prepared the specimen. Opisthocoelicaudia is the only Asian sauropod to be identified from a postcranial skull. The holotype skull was discovered and became part of the Institute of Paleobiology, Warsaw. However, it was later returned to its country of origin under the catalog number MPC D100/404. Borsuk-Bialynicka also described the type specimen and a coracoid (ZPALMgD-I/25c), both from the same locale. These bones did not fuse to one another, which indicates that they were juvenile.
In 2017, 32 sauropod fossils were found in the Nemegt Formation. These fossils could be from either Opisthocoelicaudia, or Nemegtosaurus. Two finds from the Nemegt location – a fragmentary tail and a pair claws – are indicative of Opisthocoelicaudia. They can be referred back to the former. In 2006 and 2008, field crews led by Philip Currie tried to relocate the Opisthocoelicaudia Holotype Quarry. However, they were unsuccessful in 2009. Gradzinski provided additional data that helped them succeed in 2009. Although prospection of additional bone material was impossible due to the fact that the quarry was filled with windblown sand it could be determined that the quarry is within the Nemegt Formation’s lower portion.