''Kenichthys'' is a genus of

sarcopterygian Sarcopterygii (; )—sometimes considered synonymous with Crossopterygii ()—is a clade (traditionally a class or subclass) of vertebrate animals which includes a group of bony fish commonly referred to as lobe-finned fish. These vertebrates ar ...

fish from the

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

period, and a member of the

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Tetrapodomorpha Tetrapodomorpha (also known as Choanata) is a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish. Advanced f ...

. The only known

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of the

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

is ''Kenichthys campbelli'' (named for the

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

palaeontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Ken Campbell), the first remains of which were found in

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

in 1993.Chang, M. and Zhu, M. (1993) A new Middle Devonian osteolepidid from Qujing, Yunnan. ''Mem. Assoc. Australas. Palaeontol.'' 15 183-198 The genus is important to the study of the

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s due to the unique nature of its

nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...

s, which provide vital evidence regarding the evolutionary transition of fish-like nostrils to the

choanae.Zhu, M. and Ahlberg, P. (2004) The origin of the internal nostril of tetrapods. ''Nature'' 432 94-97

Description

''Kenichthys'' was a small tetrapodomorph, with a

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

about long. While only areas of the front of the body are known, it seems likely that ''Kenichthys'' would have been similar in general body form to other basal sarcopterygians, with two dorsal fins, paired

pectoral Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectora ...

and

pelvic fins Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

and an

anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

. An important way in which ''Kenichthys'' differed from other tetropodomorphs however is in the positioning of its posterior nostril. Whilst in other tetrapodomorphs this nostril is positioned in the roof of the mouth (the

palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sep ...

), in ''Kenichthys'' it is found at the jaw margin, between the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

and

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

Fossils

The original

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

material of ''Kenichthys'' was first described in 1993, and consists of various parts of the

skull roof The skull roof or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes, including land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In com ...

lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

and

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...

. They were found in Southwestern China, in the Chuandong Formation in

Yunnan province Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...

, and are now housed in the Institute of Vertebrate Paleontology and Paleoanthropology,

Beijing Beijing, Chinese postal romanization, previously romanized as Peking, is the capital city of China. With more than 22 million residents, it is the world's List of national capitals by population, most populous national capital city as well as ...

. The fossils date from the early Devonian, specifically from the Emsian period, about 395 million years ago. Further material from the skull was later found, and described in 2004. It was this material that established the presence of a transitional external nostril in the species’ skull.

Evolutionary significance

''Kenichthys'' is important to the study of the evolution of tetrapods due to the nature of its nostrils. Most non-tetrapod vertebrates (e.g. actinopterygians) possess two sets of nostrils, one set at either end of the

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...

, and both sets of which are external. These nostrils play no part in respiration, instead serving an

olfactory The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

role. However, in all

crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...

tetrapods and many

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

tetrapods one set of nostrils is found exteriorly, and another interiorly, in the roof of the palate. This arrangement means that the nasal passage leads from the outside of the body into the

mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

. The ‘inner set’ of nostrils are known as choanae, and allow tetrapods to breathe through their

nose A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the ...

. Prior to the description of ''Kenichthys’'' nasal passages, exactly how the transition between these two forms had taken place was a source of debate. Various suggestions had been put forward including that the choana was homologous to either the posterior or anterior nostril of non-tetrapods, that it had ‘budded off’ from one of these passages, or that it was an entirely novel form, unrelated to either of the other nostrils. The debate was further complicated by the fact that

lungfish Lungfish are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, inc ...

es, another group of sarcopterygian fish, also possess a choana with a different form to that of tetrapodomorphs.Panchen, A. L. The nostrils of choanate fishes and early tetrapods. (1967) ''Biol. Rev.'' 42 374–420 The character state of the nostrils of ''Kenichthys'' demonstrates that the vertebrate choana did in fact evolve by migration of the posterior external nostril around the jaw and up onto the roof of the mouth. ''Kenichthys'' suggests that this migration took place on the route between the premaxilla and the maxilla. This evolutionary transition appears to have left its mark on tetrapod

development Development or developing may refer to: Arts *Development (music), the process by which thematic material is reshaped * Photographic development *Filmmaking, development phase, including finance and budgeting * Development hell, when a proje ...

. A

cleft palate A cleft lip contains an opening in the upper lip that may extend into the nose. The opening may be on one side, both sides, or in the middle. A cleft palate occurs when the palate (the roof of the mouth) contains an opening into the nose. The ...

may form in

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s (and other tetrapods) where the tissues that will become the premaxilla and the maxilla fail to join during development. This condition is similar to the situation found in ''Kenichthys''.

Systematics

''Kenichthys'' has consistently been seen as one of the most basal tetrapodomorphs since its discovery. Below is a recent

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

modified from Swartz, 2012:

References

{{Taxonbar, from=Q3814561 Tetrapodomorpha Prehistoric lobe-finned fish genera Early Devonian sarcopterygians Devonian sarcopterygians of Asia Prehistoric animals of China Fossil taxa described in 1993 Emsian genera

Description

Fossils

Evolutionary significance

Systematics

See also

References