''Squatinactis'' is a genus of extinct

elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of g ...

Chondrichthyes 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 tissu ...

known from the Carboniferous aged

Bear gulch limestone The Bear Gulch Limestone is a limestone-rich geological lens in central Montana, renowned for the quality of its late Mississippian-aged fossils. It is exposed over a number of outcrops northeast of the Big Snowy Mountains, and is often considere ...

Montana Montana () is a U.S. state, state in the Mountain states, Mountain West List of regions of the United States#Census Bureau-designated regions and divisions, division of the Western United States. It is bordered by Idaho to the west, North ...

. This fish was discovered in 1974 by Richard Lund. The

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...

, named CMNH 46133, consists of a

brain case In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

, poorly preserved

jaws Jaws or Jaw may refer to: Anatomy * Jaw, an opposable articulated structure at the entrance of the mouth ** Mandible, the lower jaw Arts, entertainment, and media * Jaws (James Bond), a character in ''The Spy Who Loved Me'' and ''Moonraker'' * ...

and

gill A gill () is a respiratory organ that many 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 respiration on land provided they ar ...

s, a

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

, and a partial vertebral axis. This creatures most startling feature were its broad

pectoral fins Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...

which resembled those of

Stingray Stingrays are a group of sea rays, which are cartilaginous fish related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatid ...

s and Angel sharks ( ''Squatina''). The holotype specimen has about 15

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, te ...

in its jaw. This creature is named after the angel shark. Teeth found in

Derbyshire Derbyshire ( ) is a ceremonial county in the East Midlands, England. It includes much of the Peak District National Park, the southern end of the Pennine range of hills and part of the National Forest. It borders Greater Manchester to the no ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

have been tentatively identified as those belonging to ''S. caudispinatus.''

Description

''Squatinactis'' had a flattened body with a set of large

. This fish was vaguely similar to today's

stingrays Stingrays are a group of sea rays, which are cartilaginous fish related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae ...

and angel sharks. The flins were oddly pointed forward, with a length of around two feet long. It also had a long, whip-like tail with a spine (a feature analogous to some rays) that was actually a modified, secondary

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

. The snout was short and the wide mouth was equipped with a series of long conical

cladodont This is a typical Cladodont tooth, of a Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius'' Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a common category of early Devonia ...

-shaped teeth. The body was covered in a few

placoid A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

scales, but most of the surface was bare.

Classification

Because of the bizarre nature of ''Squatinactis,'' it is somewhat difficult to classify. In the original study conducted in 1974, Lund noted that the teeth of this fish are

Cladodont This is a typical Cladodont tooth, of a Glikmanius.html" ;"title="shark called ''Glikmanius">shark called ''Glikmanius'' Cladodont (from Latin cladus, meaning branch and Greek Odon, meaning tooth) is the term for a common category of early Devonia ...

is design, however the term "cladodont" is used to describe many

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

chondrichthyeans based on their teeth and not

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...

(including ''

Cladoselache ''Cladoselache'' is an extinct genus of shark-like chondrichthyan (cartilaginous fish) from the Late Devonian ( Famennian) of North America. It was similar in body shape to modern lamnid sharks (such as mako sharks and the great white shark), ...

'', ''

Ctenacanthus ''Ctenacanthus'' (from el, κτείς , 'comb' and el, ἄκανθα , 'spine') is an extinct genus of ctenacanthiform chondrichthyan. Remains have been found in the Bloyd Formation in Arkansas, United States (Carboniferous period) and in Sout ...

'', and ''

Dracopristis ''Dracopristis'' is an extinct genus of ctenacanth (a group of shark-like elasmobranchs) that lived around 307 million years ago, during the Pennsylvanian sub-period of the Carboniferous period. The fish had 12 rows of short, squat teeth, and ...

''). This fish is currently classed within the

Elasmobranchii Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of g ...

, more specially in its own grouping, the Squatinactiformes.

Ecology

This fish was probably a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

predator; it probably lived half-buried in the sand and suddenly emerged to throw itself against the prey swimming nearby. The wing-like fins and long tail were most likely useful for propulsion from the seabed. The flattened body plan is typical of bottom-dwelling predators, and is known in a large number of cartilaginous fish, both extinct and

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

References

{{Taxonbar, from1=Q3967456, from2=Q111036391, from3=Q111036388, from4=Q35135303 Prehistoric cartilaginous fish genera Species described in 1974 Elasmobranchii