Edaphodon kawai
Not to be confused with Kahawai

Edaphodon kawai was a prehistoric chimaeriforme
Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish , spookfish , or rabbitfishes...

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...

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 belonging to the 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...

Edaphodon was a prehistoric chimaeriforme fish genus belonging to the family callorhinchidae. Edaphodon was a type of rabbitfish, a cartilaginous fish related to sharks and rays, and indeed some rabbitfishes are still alive today. Edaphodon has under fifteen known species, all of which are extinct...

, of which all the species are now extinct. Edaphodon kawai was a type of rabbitfish, a cartilaginous fish
Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...

 related to shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....

s and rays
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...

, and indeed, some rabbitfishes are still alive today. Edaphodon 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
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

. Indeed, even other with chimaeroformes, only a handful have been discovered in the Southern Hemisphere.Chimaeriformes first appeared during the Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 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 , 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...

 at the height of the rabbitfish's reign. Its scientific name, kawai, means "fish" in the language of the Moriori
Moriori are the indigenous people of the Chatham Islands , east of the New Zealand archipelago in the Pacific Ocean...

, a Pacific tribe who inhabited the islands.


Like most prehistoric cartilaginous fish, 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 resricted to the Northern hemisphere. However, when the fragmental remains of Edaphodon kawai were discovered in the Chatham Islands
Chatham Islands
The Chatham Islands are an archipelago and New Zealand territory in the Pacific Ocean consisting of about ten islands within a radius, the largest of which are Chatham Island and Pitt Island. Their name in the indigenous language, Moriori, means Misty Sun...

 not far from New Zealand, the ideas of the rabbitfish range were extended. The E. kawai holotype
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...

 was discovered in the island's Takatiki Grit formation and was dated back to the Late Cretaceous.

Another point of interest for scientists were the uncharacteristic teeth E. kawai possessed. Unlike the sharks and rays they are related to, most rabbitfish have a single set of teeth that don't 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 seabed much like a cow or herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

 would do on land. However, this is not the case with E. kawai; E. kawai 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 who would only have been able to crush organic matter. E. kawai lived during the Late Cretaceous. During this time, the rabbitfish reached their height in diversity and E. kawais tooth differences prove to scientists that the rabbitfish at that time were able to evolve into new situations.

However, some have argued that the remains of E. kawai are actually that of another prehistoric cartilaginous fish, Ischyodus
Ischyodus is an extinct genus of cartilaginous fish belonging to the subclass Holocephali, which includes the modern-day chimaeras. Fossils are known from Europe , North America, and New Zealand....

. Ischyodus lived about the same time and has in the past also been compared to the rabbitfish Chimaera monstrosa
Chimaera monstrosa
Chimaera monstrosa, also known as the rabbit fish or rat fish, is a species of fish in the Chimaeridae family.-Anatomy and appearance:...

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