Skeletal reconstruction of Opisthocoelicaudia skarzynskii. Neck and head are not in the fossil record.

  • Mongolia ( Nemegt Formation)
  • Opisthocoelicaudia skarzynskii

Opisthocoelicaudia is a genus of sauropod dinosaur from the group of Titanosauria. Fossil remains of this genus are from the Late Cretaceous (late Campanian to early Maastrichtian ) Mongolia ( Nemegt Formation).

So far, a well-preserved, partly in anatomical composite of found skeleton is known, only the neck and skull is missing - thus Opisthocoelicaudia is one of the most complete fossil traditional Titanosauria. The genus was originally thought to be a representative of the Camarasauridae, but is now regarded as very derived ( advanced ) Representatives of Saltasauridae within the Titanosauria. Sometimes Opisthocoelicaudia is grouped with the related Alamosaurus within a Opisthocoelicaudiinae mentioned group. The only way is Opisthocoelicaudia skarzynskii.

  • 6.1 support function of the tail
  • 6.2 footprints


Opisthocoelicaudia was like all sauropods, four-legged running a herbivore with a barrel-shaped body and a long neck and tail. It was a relatively small sauropod - Paul ( 1997) estimates the nearly complete example on a length of 11.3 meters and a weight of 8.4 tons. A recent study by Packard and colleagues ( 2009), meanwhile, assumes a weight of 13 tons.

Skull and neck are in the fossil record - but suggests a reconstruction of the neck bands ( ligamentum nuchae ) on a neck of medium length back that was worn horizontal or inclined slightly downward. The tail was relatively short, as in the related Alamosaurus with about 35 caudal vertebrae. As with other derived Titanosauria missing additional mechanical connection elements of the vertebrae ( Hyposphen Hypantrum - compounds), which resulted in a more flexible rear spine, while an additional sixth sacral vertebrae, the pelvic region amplified. The dorsal spine was straight. While traditional reconstructions assume a substantially horizontally oriented backs, showing Daniela Schwarz and colleagues ( 2007) that the back actually fell backwards. Thus, the shoulder blade (scapula ) at an angle of about 55 ° to 60 ° relative to the horizontal was much steeper oriented as was previously assumed, leading to a raised shoulder region. The vertebrae of the anterior caudal half were strong opisthocoel, that is, they were concave on the convex front and on the back side. This feature is eponymous for Opisthocoelicaudia and distinguishes the genus from all other Titanosauria which anterior caudal vertebrae were usually characterized by highly procoele (on the front concave and convex on the back ). Another unique ( autapomorphes ) feature were the forked spinous processes of the presacral ( located in front of the sacrum) vertebrae.

The ischial ( ischium ) was relatively short, as in many other Titanosauria and made in Opisthocoelicaudia only 2 /3 of the length of the pubis ( pubic ) from. Unlike other Titanosauria pubic and ischial were fused together. The columnar legs were robust and relatively short as in other Titanosauria. The forelimbs were found with the specimen 1.87 meters high, measured from the highest point of the upper arm bone ( humerus), and account for about two-thirds the length of the hind legs, which were reconstructed with a height of 2.64 meters. As with other Titanosauria legs were slightly bent outwards, and were not exactly perpendicular under the body, as in other sauropods.

The forefoot consisted only of the five vertically standing and semi- circularly arranged metacarpal bone - as with all Titanosauria missing carpal bones ( carpal bones ). Phalanges, which were often present as extremely reduced remainder in other Titanosauria were missing completely at Opisthocoelicaudia. The ankle bone ( astragalus ) of the ankle joint was greatly reduced, as with other Titanosauria; the heel bone ( calcaneus ) seemingly lacking completely in Opisthocoelicaudia. In contrast to the foot skeleton skeleton hand pointing to the typical sauropod well developed phalanges and claws. The Phalangenformel ( are number of phalanges in each toe ) is 2-2-2-1-0. To date, two more full Fußskelette have only been discovered by titanosaurs, but show a different Phalangenformel.

In 10 of the 40 known genera Titanosaurier osteoderms ( dermal bones plates) could be detected. Since Opisthocoelicaudia despite a residual skeleton completely preserved no osteoderms were found, researchers consider it likely that this species actually had no osteoderms. Others, known by relatively complete skeletons Titanosaurier without osteoderms are Alamosaurus, Epachthosaurus and Phuwiangosaurus. This shows that osteoderms were acquired several times in the evolution of Titanosauria independently.

Fossil record, history of discovery and naming

The type specimen ( specimen number ZPAL MgD-I/48 ) is a skull -less ( postkraniales ) skeleton, the missing only the cervical vertebrae. The site, Altan Ula IV, located in the Aimag südmongolischen Ömnö Gobi and is part of Nemegt lineup, the youngest of the three geological formation of the Nemegt Basin. Altan Ula IV is famous for a variety of vertebrate fossils - among the finds are in addition to the Opisthocoelicaudia skeleton example of Troodontide Borogovia and Ankylar Tarchia. The skeleton belonged to an old individual. The majority of vertebral found has been preserved as a series in the anatomical composite consisting of 8 vertebrae, sacrum vertebrae 6 and 34 caudal vertebrae. 3 more, poorly preserved vertebrae were found isolated from the series and probably belonged to the transition region between the neck and back spine. The remaining parts of the skeleton were shifted slightly from the original anatomical network.

In addition to this skeleton was also a scapula with coracoid ( coracoid ) described ( copy number ZPAL MgD-I/25c ), which belonged to a young individual, as evidenced by the not yet fused suture between these two bones. Researchers led by Philip Currie also mention a fragmentary tail ( copy number MPD 100/406 ), which also Opisthocoelicaudia can be attributed. This finding comes from the Nemegt locality from which is derived including the Nemegtosaurus Skull.

The type specimen was discovered by geologists Riszard Gradzinski between 10th and June 23, 1965 during the Polish- Mongolian expedition. The transport of Opisthocoelicaudia skeleton also exhibited the very rough terrain the expedition team with major technical problems: The skeleton was embedded in hard sandstone and had in blocks using slide over a distance of 580 meters to the next, can be achieved with vehicles space to be brought. The blocks consisting of fossil bone and surrounding rock, weighing a total of about 12 tons. On July 9, the packaging of the skeleton began in 35, partly a ton heavy boxes, which were then transported to Dalandsadgad. Currently, the skeleton in the Institute of Geology of the Mongolian Academy of Sciences Ulaanbaatar collection.

The genus was described in 1977 by Maria Magdalena Borsuk - Bialynicka first time scientifically. The name alludes to the special construction of the caudal vertebrae of ( ancient Greek opisthe - "rear", koilos - " hollow", and Latin cauda - "tail "). The second part of the species name, skarzynskii honors Wojciech Skarżyński, the taxidermist of the skeleton.


The type specimen shows bite marks especially on the pelvis and right thigh bone, which shows that carnivores have eaten the carcass of the animal. Head and neck of the otherwise perfectly preserved skeleton are missing, suggesting that the predator could have carried off these body parts. The skeleton is found in the supine position. It is significant that the left leg and rib bones on the right side of the body found, while, conversely, the right leg and rib bones were found on the left side of the body. Probably the carcass was transported only for a short time of a flood event and afterwards buried by sediment before the soft tissue is completely westernized. After this point the most part only weakly shifted from their original anatomical position bone.


Initially was Opisthocoelicaudia as a representative of the Camarasauridae, another group of sauropods, which should include, among others, Camarasaurus and Euhelopus with, but is no longer recognized. This assignment was due mainly to the forked low spinous processes of the vertebrae. The Erstbeschreiberin Borsuk - Bialynicka arranged to Opisthocoelicaudia the Euhelopodinae, which was then run as a subfamily within the family Camarasauridae. Coombs and Molnar (1981 ) placed the genus within the meanwhile Camarasaurinae one, another subfamily of Camarasauridae. Only in 1993 could Salgado and Coria show that there was indeed a Titanosaurier: Sun, showed Opisthocoelicaudia and other derived Titanosauria many common features ( synapomorphies ), including, for example, a sixth sacral vertebra, opisthocoele vertebrae, missing phalanges, a shortened ischium ( ischium ) missing Hyposphen - Hypantrum compounds of the vertebral arches or a crescent-shaped chest (sternum ). Salgado and Coria ( 1993) found Opisthocoelicaudia to Titanosauridae, a commonly used name in the past, but which is considered by many researchers today as invalid. Instead, sometimes the name Lithostrotia is used, which describes the same group, which is also evidenced by the name Titanosauridae.

Almost all phylogenetic analyzes come to the conclusion that Opisthocoelicaudia is closely related to the North American genus Alamosaurus. Both genera are usually considered to be close relatives of Saltasaurus and Neuquensaurus - the latter genera are grouped together as Saltasaurinae. Some researchers see Alamosaurus and Opisthocoelicaudia as a monophyletic group, called the Opisthocoelicaudiinae and Saltasaurinae is compared. Other researchers classify both genera as outgroups the Saltasaurinae, where they consider the Opisthocoelicaudiinae as paraphyletic. The grouping Saltasaurinae Opisthocoelicaudia Alamosaurus is also called Saltasauridae. In contrast to most other recent analyzes comes Curry Rogers (2005 ) found that Alamosaurus Opisthocoelicaudia and were related merely removed with the Saltasaurinae. Upchurch and colleagues ( 2004), meanwhile, see Alamosaurus and Opisthocoelicaudia not as close relatives - while they classify Alamosaurus outside the Saltasauridae as sister taxon of Pellegrinisaurus, arrange a Opisthocoelicaudia within the Saltasauridae.

Here are two examples Cladogram - with monophyletic Opisthocoelicaudiinae ( Wilson 2002, left) and with paraphyletischer Opisthocoelicaudiinae ( Calvo and González Riga in 2003, right):









Synonymy with Nemegtosaurus

Another sauropod Nemegt the lineup is Nemegtosaurus, which is only known by a skull Fund. From Opisthocoelicaudia, meanwhile, is only the residual skeleton known, which precludes direct anatomical comparisons. Several researchers suggest that it is both genera are one and the same species is ( synonymy ). According to the International Regulations for Zoological Nomenclature ( ICZN ) would in such a case, the first assigned name - in this case Nemegtosaurus - validity; the name Opisthocoelicaudia would then be invalid.

Borsuk - Bialynicka holds a synonymy in their first description as unlikely as it saw both genera as representatives of various groups. So they classified as Opisthocoelicaudia Camarasauriden while she attributed Nemegtosaurus in accordance with the opinion of the former research Dicraeosaurinae. They also argued that several sauropod species at the same time in the same place were not uncommon, as other fossil sites such as the Morrison Formation with more than five at the same time living sauropod species show.

Meanwhile, both genera are classified within the Titanosauria why, for example, Wilson ( 2005) noted that a synonymy can not be excluded. Currie and colleagues ( 2003) hold a synonymy very likely and report a fragmentary tail Opisthocoelicaudia can be attributed to and comes from the same locality as the Nemegtosaurus Skull. To finally answer the question, however, other findings are needed.


The Opisthocoelicaudia fossils come from the Nemegt formation, a geological formation that is open in the Gobi Desert in southern Mongolia. While her age has never been dated radiometrically - the fossil fauna, however, indicates that they came to deposit ( 72-66 million years) during the Maastrichtian. Large river beds and soil residues ( paleosols ) indicate a relatively humid climate, which is in contrast to the semi-arid climate under which the underlying layers, the Barun - Goyot lineup and Djadochta formation, were deposited. Calichen - concretions of precipitated calcium carbonate - however, indicate to periodic droughts.

The Nemegt formation is a significant fossil site and contains one of the richest and most diverse known Dinosaurierfaunen. So Opisthocoelicaudia shared the habitat with turtles, crocodiles and birds such as Shamosuchus Gurilynia, Judinornis and Teviornis. Mammal fossils are rarely found. Dinosaur from the group of bird Beck dinosaur ( Ornithischia ) were represented with the Ankylar Tarchia, the Pachycephalosauriern Homalocephale and Prenocephale and with the Hadrosauriden Saurolophus and Barsboldia. The numerous small theropods of the formation close troodontids as Borogovia, Tochisaurus and Zanabazar, Oviraptorosaurier as Elmisaurus, Nemegtomaia and Rinchenia, Ornithomimosaurier as Anserimimus, Gallimimus and Deinocheirus, Therizinosauroideen Therizinosaurus as well as the Dromaeosauriden Adasaurus and Tyrannosauroideen Bagaraatan and Alioramus with a. Spitzenprädator fauna - and possibly predator of Opisthocoelicaudia - was the Tyrannosauride Tarbosaurus. Besides Opisthocoelicaudia is represented by Nemegtosaurus a second sauropod species.


Support function of the tail

Borsuk - Bialynicka suspected that the tail could have allowed as a kind of third leg an erection on his hind legs, for example, in search of food. She argued that the tail thanks to the opisthocoelen caudal vertebrae was more flexible than other sauropods. Also features on the pelvic bone, as a deepened acetabulum ( acetabulum ) with thickened edge, would support this theory. Some recent studies interpret other features, such as with only about 35 caudal vertebrae greatly shortened tail as possible indications of a support function of the tail at Opisthocoelicaudia and other Saltasauriden.


Fossil footprints are very rarely found in the Nemegt lineup. Various footprints, which mainly come from Hadrosauriden could be exposed in the Nemegt locality - including at least two footprints that were generated by the hind leg of a sauropod. Currie and colleagues ( 2003) assign these traces of the genus Opisthocoelicaudia what is justified by the very similar morphology of the footprints and the foot skeleton of Opisthocoelicaudia - type copy. While it is possible that the footprints are in fact from another related species. This is unlikely this according to researchers as they consider Nemegtosaurus and Opisthocoelicaudia as synonyms, and thus only postulate a single sauropod species in the Nemegt fauna.

In both kick seals is three-dimensional casts of the actual, no longer extant prints. The best preserved sauropod footprints measuring 63 centimeters in diameter and probably belonged to an animal that was slightly larger than the Opisthocoelicaudia - type specimen. Although the lower ( ventral ) is hardly obtained surface, the vertical, lateral surfaces are very well preserved: it even show a skin print, which shows the non- overlapping scales with an average diameter of 14 millimeters. The tracking generator wore two or three claws on each hind foot, the toes were almost perpendicular ( digitigrade ). The foot of the track generator was probably a little longer than wide.

Further Reading

  • M. Borsuk - Bialynicka (1977 ): A new sauropod camarasaurid Opisthocoelicaudia skarzynskii Gen. n, sp. n from the Upper Cretaceous of Mongolia. Palaeontologia Polonica 37, pages 5-64. (PDF)
  • Z. Kielan - Jaworowska, N. Dovchin (1969 ): Narrative of the Polish - Mongolian Expeditions 1963-1965 - Results Polish - Mong. Pal. Exp I. In: Palaeontologia Polonia, number 19 (PDF)
  • L. Salgado, RA Coria, 1993: Considerations on the phylogenetic relationships of Opisthocoelicaudia skarzynskii ( Sauropoda ) from the Upper Cretaceous of Mongolia. ( Original title: Consideraciones sobre las relaciones de filogeneticas Opisthocoelicaudia skarynskii ( Sauropoda ) del Cretácico superior de Mongolia. ) In: X jornadas Argentinas de Paleontologia de Vertebrados. Abstract translated by Jeffrey Wilson (Abstract in Doc format).
  • Philip J. Currie, Demchig Badamgarav, Eva B. Koppelhus. 2003rd The First Late Cretaceous Footprints from the Nemegt Locality in the Gobi of Mongolia. In: Ichnos, 10, pp. 1-12, doi: 10.1080/10420940390235071
  • Daniela Schwarz, Eberhard Frey, Christian Meyer (2007): Novel Reconstruction of the Orientation of the Pectoral Girdle in sauropods. In: The Anatomical Record, 290 pages 32-47. (PDF)