Kaganaias
Encyclopedia
Kaganaias is an extinct genus
of mosasaur
oid lizard
that lived in what is now Japan
during the Early Cretaceous
. Kaganaias was semi-aquatic and is the only known aquatic squamate to be found in Asia
and is also the only known aquatic squamate known from before the Cenomanian
stage of the Cretaceous. It is also the first to be found in an inland area, instead of on the coast where aquatic squamates are commonly found. Its generic name is derived from Kaga Province
, the old name for the Ishikawa Prefecture
where the specimens were found, while the species name hakusanensis comes from the mountain that gives its name to Hakusan
the city near its find site. The geological formation in which the specimens were found, the Tetori Group, stands alongside the Tetori River and has been the site of numerous other finds including molluscs, dinosaur
s, fish
and pterosaur
s.
Although Kaganaias is known to be in the Mosasaur family, it is unclear where; it has been assigned to Platynota
(Varanoidea
) for the time being.
specimen was a partial skeleton, including numerous ribs, vertebrae and parts of the limbs and tail, whilst the secondary specimen had extra ribs and sections of the skull
also, notably parts of the maxilla
. The body of Kaganaias was both long and broad across the chest, but was predominantly flat. Despite being classified as a lizard, Kaganaias has numerous snake-like features. Sexual dimorphism
may have been present in the species, but this is uncertain due to the paucity of data.
Kaganaias lived in what was a fertile, inland swamp
-like region of Japan, possibly a large floodplain which was covered with water for most of the year. The fossil itself was discovered by a construction team preparing to lay down a new tunnel through a fossil cliff in 1997.
Kaganaias almost certainly moved through the water using a snake-like swimming motion, using its short hind legs to navigate. Kaganaias probably fed on other small vertebrates or molluscs which have been found in the surrounding area, but this has yet to be confirmed by the results of the examination of the fossil's faecal remains.
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 mosasaur
Mosasaur
Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...
oid lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
that 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...
during the Early Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
. Kaganaias was semi-aquatic and is the only known aquatic squamate to be found in Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
and is also the only known aquatic squamate known from before the Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
stage of the Cretaceous. It is also the first to be found in an inland area, instead of on the coast where aquatic squamates are commonly found. Its generic name is derived from Kaga Province
Kaga Province
was an old province in the area that is today the southern part of Ishikawa Prefecture. It was sometimes called .Ruled by the Maeda clan, the capital of Kaga was Kanazawa. Kaga bordered on Echizen, Etchū, Hida, and Noto Provinces...
, the old name for the Ishikawa Prefecture
Ishikawa Prefecture
is a prefecture of Japan located in the Chūbu region on Honshū island. The capital is Kanazawa.- History :Ishikawa was formed from the merger of Kaga Province and the smaller Noto Province.- Geography :Ishikawa is on the Sea of Japan coast...
where the specimens were found, while the species name hakusanensis comes from the mountain that gives its name to Hakusan
Hakusan, Ishikawa
is a city located in Ishikawa, Japan.The city was founded on February 1, 2005 from the merger of the city of Mattō with seven towns and villages from Ishikawa District. As of April 1, 2008 population data, the city has an estimated population of 110,654 and a density of 147 persons per km²...
the city near its find site. The geological formation in which the specimens were found, the Tetori Group, stands alongside the Tetori River and has been the site of numerous other finds including molluscs, 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...
s, fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s.
Although Kaganaias is known to be in the Mosasaur family, it is unclear where; it has been assigned to Platynota
Platynota
Platynota is a group of anguimorph lizards. Since it was named in 1839, it has included several groups, including monitor lizards, snakes, mosasaurs, and helodermatids. Its taxonomic use still varies, as it is sometimes considered equivalent to the group Varanoidea and other times viewed as a...
(Varanoidea
Varanoidea
Varanoidea is a superfamily of lizards, including the well-known family Varanidae . Also included in the Varanoidea are such extinct marine and semi-aquatic forms as mosasaurs and dolichosaurs, the venomous helodermatids , the Lanthanotidae , and the extinct Necrosauridae.Throughout their long...
) for the time being.
Description
Kaganaias was small (roughly half a meter long), agile and had a long body. Like most of its semi-aquatic kind, Kaganaias had reduced limbs to aid in its aquatic activities. Kaganaias is known from two specimens; the holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen was a partial skeleton, including numerous ribs, vertebrae and parts of the limbs and tail, whilst the secondary specimen had extra ribs and sections of the skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
also, notably parts of the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
. The body of Kaganaias was both long and broad across the chest, but was predominantly flat. Despite being classified as a lizard, Kaganaias has numerous snake-like features. Sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
may have been present in the species, but this is uncertain due to the paucity of data.
Kaganaias lived in what was a fertile, inland swamp
Swamp
A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
-like region of Japan, possibly a large floodplain which was covered with water for most of the year. The fossil itself was discovered by a construction team preparing to lay down a new tunnel through a fossil cliff in 1997.
Kaganaias almost certainly moved through the water using a snake-like swimming motion, using its short hind legs to navigate. Kaganaias probably fed on other small vertebrates or molluscs which have been found in the surrounding area, but this has yet to be confirmed by the results of the examination of the fossil's faecal remains.