''Edaphodon kawai'' was a prehistoric

chimaeriform Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. A ...

fish Fish are aquatic, craniate, gill-bearing 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. Approximately 95% of li ...

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

belonging to the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Edaphodon ''Edaphodon'' was a fish genus of the family Callorhinchidae (sometimes assigned to Edaphodontidae). As a member of the Chimaeriformes, ''Edaphodon'' was a type of rabbitfish, a cartilaginous fish related to sharks and rays. The genus appeare ...

'', of which all the species are now extinct. ''Edaphodon kawai'' was a type of rabbitfish, a

cartilaginous fish Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue ...

related to

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...

s and

rays Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gra ...

, and indeed, some rabbitfishes are still alive today. ''E. kawai'' is one of numerous ''Edaphodon'' species, but is the only one which has been discovered in the Southern Hemisphere, near

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

. Indeed, only a handful of other Chimaeroformes have been discovered in the Southern Hemisphere. They first appeared during the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

period around 415 to 360 million years ago, but the only known specimen of ''E. kawai'' has been dated to the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

at the height of the rabbitfish's reign. Its scientific name, ''kawai'', means "fish" in the language of the

Moriori The Moriori are the native Polynesian people of the Chatham Islands (''Rēkohu'' in Moriori; ' in Māori), New Zealand. Moriori originated from Māori settlers from the New Zealand mainland around 1500 CE. This was near the time of the ...

, a

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

tribe who inhabited the islands.

Description

Like most prehistoric cartilaginous fishes, ''E. kawai'' is known from a few fragmentary remains, including teeth and a beak. ''E. kawai'' provided many new points of knowledge for scientists when it was formally described in 2006. Firstly, the range of the prehistoric ''Edaphodon'' species, and indeed all prehistoric rabbitfish, was thought to be restricted to the Northern Hemisphere. However, when the fragmental remains of ''E. kawai'' were discovered in the

Chatham Islands The Chatham Islands ( ) (Moriori: ''Rēkohu'', 'Misty Sun'; mi, Wharekauri) are an archipelago in the Pacific Ocean about east of New Zealand's South Island. They are administered as part of New Zealand. The archipelago consists of about te ...

not far from New Zealand, the rabbitfish range was extended. The ''E. kawai''

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

was discovered in the island's Takatiki Grit formation and was dated back to the Late Cretaceous. Another point of interest for scientists was the uncharacteristic teeth ''E. kawai'' possessed. Unlike the sharks and rays to which they are related, most rabbitfish have a single set of teeth that do not grow back and are used for grinding their food. These teeth, along with the position of the mouth so that it is the underside of the head, allows the rabbitfish to graze on the sea bed much like a

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

would do on land. However, this is not the case with ''E. kawai''; it had teeth which were equipped for both grinding and cutting. This opened up a range of new prey to the fish, which would have been able to scavenge food and rip flesh from decaying carcasses, unlike others in its group, which would only have been able to crush organic matter. ''E. kawai'' lived during the Late Cretaceous. During this time, the rabbitfish reached their maximum in diversity. However, some have argued that the remains of ''E. kawai'' are actually those of another prehistoric cartilaginous fish, ''

Ischyodus ''Ischyodus'' (from el, ισχύς , 'power' and el, ὀδούς 'tooth') is an extinct genus of chimaera. It is the most diverse and long-lived chimaera genus, with over 39 species found worldwide spanning over 140 million years from the M ...

'', which lived about the same time and has also been compared to the rabbitfish ''

Chimaera monstrosa ''Chimaera monstrosa'', also known as the rabbit fish or rat fish, is a northeast Atlantic Ocean, Atlantic and Mediterranean Sea, Mediterranean species of cartilaginous fish in the family Chimaeridae. The rabbit fish is known for its characteris ...

''.

References

* Consoli, C.P. (December, 2006). Edaphodon kawai, sp. nov. (Chondrichthyes: Holocephalei): A Late Cretaceous Chaemeroid from the Chatham Islands, Southwest Pacific.'' Journal of Vertebrate Paleontology'' 26(4):801–805.

External links

* {{Taxonbar, from=Q5335698 Callorhinchidae Extinct animals of New Zealand Cretaceous cartilaginous fish