"Futabasaurus" is an informal name

Nomen nudum

The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...

 for a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of theropod dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

 from the Late Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

 of Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

, known only from a partial shin bone

Tibia

The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....

 discovered in the Coniacian

Coniacian

The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma...

-age Ashizawa Formation

Ashizawa Formation

The Ashizawa Formation is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.-See also:* List of dinosaur-bearing rock formations...

 of the Futaba Group

Futaba Group

The Futaba Group is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.-See also:* List of dinosaur-bearing rock formations...

. It was coined by David Lambert in 1990 as a conversion from the Japanese nickname "Futaba-ryu", for an undescribed theropod. Dong Zhiming

Dong Zhiming

Dong Zhiming , from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, is one of China's leading paleontologists. He began working at the IVPP in 1962, learning from Yang Zhongjian who was director at the time...

 and coauthors briefly discussed the fossil shin bone it was based on that same year, publishing a photograph. They considered the bone to belong to an indeterminate tyrannosaurid

Tyrannosauridae

Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...

. If the specimen is eventually described and named, it will require a different name, because the name Futabasaurus

Futabasaurus

Futabasaurus is a genus of plesiosaur from the Late Cretaceous of Fukushima, Japan. Described and named in 2006, it was assigned to the family Elasmosauridae. The length was about 7 m, and the weight was about 3~4 tons. Futabasaurus is the first elasmosaurid found in Japan. The type...

has since been used for a genus of plesiosaur

Plesiosaur

Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...

.