Megalichthyidae is an extinct

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

tetrapodomorph 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 for ...

s which lived from the

Middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...

–

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

to the

Early Permian 01 or 01 may refer to: * The year 2001, or any year ending with 01 * The month of January * 1 (number) Music * '01 (Richard Müller album), ''01'' (Richard Müller album), 2001 * 01 (Urban Zakapa album), ''01'' (Urban Zakapa album), 2011 * ''01011 ...

. They are known primarily from

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

deposits, mostly in the Northern Hemisphere (Europe, the Middle East, North Africa and North America), but one genus (''

Cladarosymblema ''Cladarosymblema'' is an extinct genus of megalichthyid tetrapodomorphs which lived in Australia during the Early Carboniferous Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a s ...

'') is known from Australia, and the possible megalichthyid ''

Mahalalepis ''Mahalalepis'' is an extinct genus of megalichthyid tetrapodomorphs which lived during the Devonian period The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years ...

'' is from Antarctica.

Description

Megalichthyids were fairly primitive tetrapodomorphs, retaining a largely fish-like appearance. Like some other primitive

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 ...

s, their bodies were covered in rhomboid

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...

that possessed a layer of

cosmine Cosmine is a spongy, bony material that makes up the dentine-like layers in the scales of the lobe-finned fishes of the class Sarcopterygii. Fish scales that include layers of cosmine are known as cosmoid scales. Description As traditionally d ...

(a porous, mineralised tissue). The scales however lacked the peg-and-socket articulations found in some other groups. The skulls of megalichthyids had a rather low and broad shape. Like the scales, the

dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton, including much of the skull, jaws, gill covers, shoulder girdle, fin rays ( lepidotrich ...

s of the skull bore a layer of cosmine. The

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 were somewhat elongated, slit-like holes that were bordered in the front by the

lateral rostral bone Lateral is a geometric term of location which may also refer to: Biology and healthcare * Lateral (anatomy), a term of location meaning "towards the side" * Lateral cricoarytenoid muscle, an intrinsic muscle of the larynx * Lateral release (sur ...

and in the back by the

posterior tectal bone Posterior may refer to: * Posterior (anatomy), the end of an organism opposite to anterior ** Buttocks, as a euphemism * Posterior horn (disambiguation) * Posterior probability The posterior probability is a type of conditional probability that ...

. 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 ...

(one of the bones of the upper jaw) had a well-developed posterior process, and bore a large

tusk Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine tooth, canine teeth, as with Narwhal, narwhals, chevrotains, musk deer, water deer, muntjac, pigs, ...

that either interrupted the main tooth row or was located further inside the mouth, depending on the species. The

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 ...

(another bone of the upper jaw, located behind the premaxilla) was rather tall, especially towards the rear end. The

vomer The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

s (a pair of bones in 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 ...

) were short and broad, with a well-developed mesial process in some cases. The

lacrimal bone The lacrimal bones are two small and fragile bones of the facial skeleton; they are roughly the size of the little fingernail and situated at the front part of the medial wall of the orbit. They each have two surfaces and four borders. Several bon ...

had a prominent notch. The front end of the

parietal bone The parietal bones ( ) are two bones in the skull which, when joined at a fibrous joint known as a cranial suture, form the sides and roof of the neurocranium. In humans, each bone is roughly quadrilateral in form, and has two surfaces, four bord ...

had a concave shape where it contacted the posterior nasal bone. The

pineal foramen A parietal eye (third eye, pineal eye) is a part of the epithalamus in some vertebrates. The eye is at the top of the head; is photoreceptive; and is associated with the pineal gland, which regulates circadian rhythmicity and hormone production ...

(a hole located at the top of the skull in some vertebrates, containing the parietal eye) was absent. The

supratemporal bone The supratemporal bone is a paired cranial bone present in many tetrapods and tetrapodomorph fish. It is part of the temporal region (the portion of the skull roof behind the eyes), usually lying medial (inwards) relative to the squamosal and latera ...

had a forwards-pointing process that lacked a covering of cosmine. The

squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral ...

was nearly equal in height and width. The preopercular was a fairly short, vertically aligned bone. The opercular series (a set of bones protecting the

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s) consisted of three bones, the opercular and two suboperculars. The opercular was large and almost square-shaped. The suboperculars were in contact with the last or second-last of the submandibular bones (a group of bones lying beneath the

dentary bone 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 ...

of the lower jaw). The

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s were large and had a fan-like shape.

Classification

Megalichthys ''Megalichthys'' is a genus of prehistoric lobe-finned fish which lived during the Devonian and Carboniferous periods. It is the type genus of the family Megalichthyidae. The type species is ''M. hibberti''. The species ''M. mullisoni,'' named f ...

'', the

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

of Megalichthyidae, was historically grouped together with various other primitive tetrapodomorphs into the family Osteolepididae, starting with an 1891 article by the English palaeontologist

Arthur Smith Woodward Sir Arthur Smith Woodward, FRS (23 May 1864 – 2 September 1944) was an English palaeontologist, known as a world expert in fossil fish. He also described the Piltdown Man fossils, which were later determined to be fraudulent. He is not rel ...

. Osteolepididae is nowadays thought to be

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

, being diagnosed mainly by features that are widely distributed among tetrapodomorphs and other

osteichthyan Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

s. The family Megalichthyidae was erected in 1902 by the American palaeontologist

Oliver Perry Hay Oliver Perry Hay (May 22, 1846 – November 2, 1930) was an American herpetologist, ichthyologist, and paleontologist. Hay was born in Jefferson County, Indiana, to Robert and Margaret Hay. In 1870, Hay graduated with a bachelor of arts from ...

. Within the family, he included the genera '' Coelosteus'', ''

Eusthenopteron ''Eusthenopteron'' (from 'stout', and 'wing' or 'fin') is an extinct genus of prehistoric marine lobe-finned fish known from several species that lived during the Late Devonian period, about 385 million years ago. It has attained an iconic ...

'', ''Megalichthys'', '' Rabdiolepis'', '' Rhizodopsis'', '' Sauripteris'' and ''

Strepsodus ''Strepsodus'' is a genus of rhizodont lobe-finned fish that lived throughout the Carboniferous period. Fossils have been found in eastern Canada, Britain (England and Scotland), and Queensland, Australia; indeterminate species of ''Strepsodus'' ...

'', most of which are no longer regarded as megalichthyids. The family thereafter went into disuse for a long time, but was treated as a subfamily of Osteolepididae (as Megalichthyinae) by Vorobyeva (1977). Megalichthyidae was resurrected as a separate family in a 1992 article by Young ''et al.'', who assigned ''Megalichthys'', ''

Ectosteorhachis ''Ectosteorhachis'' is an extinct genus of freshwater megalichthyid tetrapodomorphs that inhabited what is now North America during the Permian period (Cisuralian epoch, about 299 to 272 million years ago). It is the only known member of the sub ...

'', ''

Megistolepis ''Megistolepis'' is a genus of prehistoric lobe-finned fish which lived during the Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 ...

'' and the newly described ''

'' to the group. Later studies have disagreed about which genera should be included, but it is widely agreed that at least ''Megalichthys'', ''Ectosteorhachis'' and ''

'' belong to Megalichthyidae. A few genera of "osteolepidids" (e.g. ''

Osteolepis ''Osteolepis'' (from 'bone' and 'scale') is an extinct genus of lobe-finned fish from the Devonian period. It lived in the Lake Orcadie of northern Scotland. Description ''Osteolepis'' was about long, and covered with large, square scale ...

'' and ''

Gogonasus ''Gogonasus'' (meaning "snout from Gogo") was a lobe-finned fish known from three-dimensionally preserved 380-million-year-old fossils found from the Gogo Formation in Western Australia. It lived in the Late Devonian period, on what was once a ...

'') have often been recovered in a clade with the megalichthyids. This larger clade was given the name

Megalichthyiformes Megalichthyiformes is an extinct clade of basal tetrapodomorphs which first appeared during the Devonian period. It was named in 2010 by Michael I. Coates and Matt Friedman, who defined it as a stem-based taxon containing all tetrapodomorphs clo ...

in a 2010 article, and is defined as "including all tetrapodomorph sarcopterygians more closely related to ''Megalichthys'' than ''Eusthenopteron''". Below is a

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 ...

adapted from a phylogenetic analysis by Clement ''et al.'' (2021). Here, the family

Canowindridae The Canowindridae are a family of prehistoric tetrapodomorphs which lived during the Devonian period (Famennian stage, about 374 to 359 million years ago). Fossils belonging to this family have been found in Australia, Antarctica, and Europe. P ...

was found to be the sister group of Megalichthyidae, while four "osteolepidid" genera form a basal grade leading to both groups. Megalichthys NT

Distribution

Fossils attributed to megalichthyids have been found mainly in

deposits, dating to between the

–

and the

. North American representatives of the family include ''Ectosteorhachis'', ''Megalichthys'', and the possible megalichthyids '' Lohsania'', ''Rhizodopsis'' and '' Sterropterygion''. European megalichthyids include '' Askerichthys'', ''Megalichthys'', '' Palatinichthys'', and the possible members '' Cryptolepis'', ''

'', ''

Megapomus ''Megapomus'' is a genus of prehistoric lobe-finned fish which lived during the Carboniferous period The Carboniferous ( ) is a geologic period and system of the Paleozoic era that spans 60 million years, from the end of the Devonian Period M ...

'' and ''Rhizodopsis''. Megalichthyids are also known from Morocco (''Megalichthys''), Turkey ('' Sengoerichthys''), Australia (''Cladarosymblema'') and Antarctica (''

'').

References

{{Taxonbar, from=Q1917037 Megalichthyidae Tetrapodomorph families Late Devonian first appearances Cisuralian extinctions Taxa named by Oliver Perry Hay