Nipponosaurus
Skeletal reconstruction of Nipponosaurus
- South Sakhalin
- Nipponosaurus sachaliensis
Nipponosaurus is a little known genus ornithopoder dinosaur from the group of Hadrosauridae.
The hitherto only known skeleton was discovered in 1934 in South Sakhalin, which was at that time under Japanese rule. This is the first discovered on Japanese territory dinosaurs. The find is dated to the Late Cretaceous (late Santonian to early Campanian ). The only way is Nipponosaurus sachaliensis.
Features
Nipponosaurus is considered a representative of Lambeosaurinae. While other members of this group often showed striking head combs, such a possibly existing head crest at Nipponosaurus is the fossil record. The specimen found was a young animal, as not yet fused sutures of the vertebrae show. For more information on a juvenile show, among other things in the jaw: So the number of existing tooth positions was low, the tooth batteries per tooth position only ever had two teeth in the lower jaw.
Fund and differentiation from other genres
The skeleton found ( holotype, specimen number CLOCK 6590 ) of Nipponosaurus is fully 60 % and consists of some skull bones ( including upper and lower jaw), vertebrae ( 13 cervical, 6 back, two sacral, and 35 caudal vertebrae ), a scapula, the majority of the front legs and almost complete hind legs and pelvic bone ( ilium and ischium ). The skeleton is due to the heavily eroded bone surfaces in a poor state of preservation, why Nipponosaurus one of the Lambeosaurinen the least known.
Nagao (1936 ) proposed the new genus Nipponosaurus, but could not distinguish on the basis of osteological characters of other then-known genera of Hadrosauridae, but only on the basis of geographic distance of the sites due to the poor state of preservation. Daisuke Suzuki and colleagues ( 2004) still showed in their first description detect two autapomorphies - osteological features which distinguish the genus from all related genera - which the status is confirmed as a valid genus: So was the Surangulare, a bone of the lower jaw, a robust processus coronoid. In addition, the spinous process of the second cervical vertebra (axis ) was poorly developed, while the lateral edge of the first phalanx of the fourth finger of the hand was severely dented.
Research History and naming
Parts of the skeleton were only known in the construction of a hospital in South Sakhalin Japanese (now Russia) being uncovered in November 1934. The Japanese Professor Takumi Nagao described the skeleton in 1936 as a new member of the Trachodontidae ( = Hadrosauridae ). Nagao 1937 organized an expedition with the aim to involve other parts of the skeleton: The successful company brought, among other things, the front legs and both hind feet of the skeleton revealed. Nagao described these additional findings in 1938. A redescription of the genus by Suzuki and colleagues appeared in 2004.
The name Nipponosaurus means as much as " Japan lizard" (Japanese Nippon - "Japan", gr sauros - "lizard "). The second part of the species name, sachaliensis, refers to the locality, the island of Sakhalin.
System
Suzuki and colleagues ( 2004) provide Nipponossaurus to Lambeosaurinae, one of two subfamilies of Hadrosauridae. This assignment is based on two common characteristics ( synapomorphies ): So the nasal bone is excluded from the formation of the nostrils; Also the teeth of the dentary is extended. Within the Lambeosaurinae Nipponosaurus is most associated with the group Corythosaurini. According to the phylogenetic analysis of Suzuki and colleagues Nipponosaurus forms a clade with Hypacrosaurus altispinus; both species form the sister group to Corythosaurus and Lambeosaurus. A recent analysis by Evans and Reisz (2007 ) provides Nipponosaurus however, as basalsten ( pristine ) Representatives of Corythosaurini.
Below is a cladogram by Evans and Reisz, 2007:
Hadrosaurinae
Nipponosaurus
Lambeosaurus
Corythosaurus
Hypacrosaurus