Nipponosaurus

*Nipponosaurus sachalinensis*

**Nipponosaurus** (meaning Japan reptile) is a Lambeosaurine hadrosaur from late Cretaceous Russia. It was about 26.2 ft (8 m) long and weighed as much as a rhinoceros. A not-fully-grown specimen, very similar to North America's Hypacrosaurus.

## History of study

The holotype (UHR 6590, University of Hokkaidō Registration) was discovered in November 1934 during the construction of a hospital for the Kawakami colliery of the Mitsui Mining Company on Karafuto Prefecture (now Sinegorsk, Sakhalin, Russia), and additional material belonging to the specimen was recovered in the summer of 1937. The type species *Nipponosaurus sachalinensis* was in 1936 named and described by Professor Takumi Nagao of the Imperial University of Hokkaido. The generic name refers to Nippon, the Japanese name of Japan; it was the first dinosaur named based on a find made on Japanese territory — though South Sakhalin was annexed by the Soviet Union in 1945. The specific name refers to Sakhalin. In 1938 Nagao dedicated a second article to the species.

The specimen was collected from Upper Yezo Group ("Upper Ammonites Bed) (late Santonian — early Campanian). UHR 6590 consists of a left maxilla and dentary, parietal, various isolated skull elements, thirteen cervical vertebrae, six dorsal vertebrae, two sacral vertebrae, a series of 35 caudal vertebrae, a left scapula, distal portions of both humeri, most elements of the lower forelimbs, an ischium, left ilium, and most of the hindlimbs. Though the quality of bone preservation is generally poor, the skeleton is estimated to be 60% complete. It nevertheless remains one of the most poorly known lambeosaurine dinosaurs.

## Discovery

*Nipponosaurus* was recently redescribed by Suzuki et al. (2004), who diagnosed the taxon as follows: "Robust coronoid process of the surangular, only slight development of the neural spine of the axis, and strong deflection of the lateral margin of the first phalanx of digit IV."

Suzuki et al. (2004) have determined that the holotype represents a subadult individual, measuring roughly four meters (13 feet) in length. A cladistic analysis (Suzuki et al., 2004; pp. 160–161) places *Nipponosaurus sachalinensis* very close to the well-known North American *Hypacrosaurus altispinus* within the Lambeosaurinae. They denied the taxon was a *nomen dubium* as has been concluded by several authors.

## Description

The immature holotype specimen measures roughly Template:Convert in length. When it was originally described, it was considered to be an adult, because of its co-ossified sacral vertebra. Future authors doubted this, merely citing its small size. In the 2004 redescription, it was examined more closely and several characteristics were found that identified it as an juvenile individual. Later, in 2017, another team re-evaluated the specimen, and determined through investigating the fossils at a microscopic level (in a process called histology) that this was correct, although they doubted the significance of some of the characters identified in the former study.

Though the quality of bone preservation is generally poor, the holotype skeleton is estimated to be 60% complete. It consists of a left maxilla and dentary, parietal, various isolated skull elements, thirteen cervical vertebrae, six dorsal vertebrae, two sacral vertebrae, a series of 35 caudal vertebrae, a left scapula, lower portions of both humeri, most elements of the lower forelimbs, an ischium, left ilium, and most of the hindlimbs.

## Classification

Some authors have deemed the species a *nomen dubium*, questioning its supposed diagnostic characteristics, especially in light of its presumed immature status. The validity of the taxon has therefore been controversial. The 2004 redescription denied this, proposing three diagnostic characters. In their description of *Sahaliyania* and *Wulagasaurus*, Pascal Godefroit and colleagues reported based on direct observation of the type specimen that all of these supposed unique traits were found in other hadrosaurids. The lack of certain portions of the skull key to evaluating its systematic position was also cited as a reason to doubt the validity of the genus, and the problematic nature of the skull had indeed been noted before. Later, a 2017 study once again questioned the validity of the proposed diagnostic characters; however, upon a re-examination of the specimen, three new ones were put forward.

A cladistic analysis in 2004 placed *Nipponosaurus sachalinensis* very close to the well-known North American *Hypacrosaurus altispinus* within the Lambeosaurinae. They suggested it might be congeneric with the species, but because of the incomplete nature of the holotype and the questionable monophyly of the genus *Hypacrosaurus*, they refrained from reassigning it. However, later in 2007, a study providing a redescription of *Lambeosaurus magnicristatus* re-evaluated a character relating to the size of the distal ischial foot, and found this drew *Nipponosaurus* away from *H. altispinus* and into a more basal position within their Corythosaurini (now generally referred to as the Lambeosaurini). They however noted the only character uniting it specifically with this group, an increased number of cervical vertebrae, was a state poorly known in more basal Asian lambeosaurines, and cautioned its position was likely liable to change. The left cladogram was recovered in the 2004 study, and the right cladogram was recovered by the 2007 study:

More recently, another analysis, accounting for characters that vary through ontogeny, instead found it to be closely related to the European taxa *Arenysaurus* and *Blasisaurus*, outside of Lambeosaurini, unlike the earlier studies. Its position outside of the clade containing Parasaurolophini and Lambeosaurini was supported by the absence of two synapomorphies of the group in its teeth. Four characters united it with *Arenysaurus* and *Blasisaurus*; the end margin of the coronoid process overlapping with the back portion of the dental battery (which was suggested to perhaps reflect a difference in feeding habits from other taxa), a short edentulous slope, and two characters of the jugal. The following cladogram was recovered in their analysis:

## Paleoecology

The specimen was collected from Upper Yezo Group, which was known as the Upper Ammonites Bed at the time of the original description. Because the area where it was discovered no longer belongs to Japan, follow up research has become difficult. Additionally, field notes from the time of discovery have been lost. This has made determining the age of the horizon problematic. However, Nagao noted fossil molluscs now called *Parapuzosia japonica* and *Sphenoceramus schmidti* were also found at the locality, and these are known to hail from the lower Campanian. An age from the upper Santonian or lower Campanian is therefore likely.

Based on the sediments it was preserved in, the *Nipponosaurus* specimen is thought to have been buried in a marine setting. However, this would not have been far from the shore, as indicated by the relatively complete nature of the specimen and the presence of fossilised terrestrials plants found alongside it. This indicates the species may have lived primarily on low-lying plains near the coast, a lifestyle consistent with some of its North American relatives.

## Appearance in other media

### *Jurassic Park*

*Nipponosaurus* is seen on the Holoscape screen in the Innovation Center of Jurassic World, though it is currently unknown if any reside within the park itself.

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Cite error: Invalid `<ref>` tag; no text was provided for refs named `desc2004`
2. ↑ 2.0 2.1 2.2 2.3 Cite error: Invalid `<ref>` tag; no text was provided for refs named `desc2017`
3. ↑ 3.0 3.1 3.2 Cite error: Invalid `<ref>` tag; no text was provided for refs named `matsukawa`
4. ↑ Template:Cite journal
5. ↑ Template:Cite journal