"Katsuyamasaurus" is the informal name given to an as yet undescribed 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 Early Cretaceous

Early Cretaceous

The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...

. It was a carnosaur which lived in what is now 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...

. The type species

Type species

In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...

 was coined by Lambert in 1990, but is not formally described, making it a nomen nudum

Nomen nudum

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

. "Katsuyamasaurus" is known from remains including an ulna

Ulna

The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...

 and a vertebra, and is named after the locality in Japan where the fossils were found. After the publication of Fukuiraptor

Fukuiraptor

Fukuiraptor was a medium-sized carnivore of the Early Cretaceous that lived in what is now Japan. Scientists first thought it was a member of the Dromaeosauridae, but after studying the fossils they now believe it was related to Allosaurus in the family Neovenatoridae. The type specimen is the...

, George Olshevsky

George Olshevsky

George Olshevsky is a freelance editor, writer, publisher, amateur paleontologist, and mathematician living in San Diego, California.Olshevsky maintains the comprehensive online Dinosaur Genera List...

suggested that "Katsuyamasaurus" could be a synonym, but a formal synonymization has not yet occurred.