The bigeye sand tiger (''Odontaspis noronhai'') is an extremely rare

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 appropriat ...

mackerel shark The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of sharks commonly known as mackerel sharks (which may also refer specifically to the family Lamnidae). It includes some of the most familiar species of sharks, such as the gre ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Odontaspididae, with a possible worldwide distribution. A large, bulky species reaching at least in length, the bigeye sand tiger has a long bulbous snout, large orange eyes without

nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. All ...

s, and a capacious mouth with the narrow teeth prominently exposed. It can be distinguished from the similar smalltooth sand tiger (''O. ferox'') by its teeth, which have only one lateral cusplet on each side, and by its uniformly dark brown color. Inhabiting

continental margin A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

s and oceanic waters at depths of , the bigeye sand tiger may make

vertical Vertical is a geometric term of location which may refer to: * Vertical direction, the direction aligned with the direction of the force of gravity, up or down * Vertical (angles), a pair of angles opposite each other, formed by two intersecting s ...

and horizontal migratory movements. It feeds on

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartil ...

es and

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fittin ...

, and its sizable eyes and dark coloration suggest that it may spend most of its time in the

mesopelagic zone The mesopelagic zone ( Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins a ...

. Reproduction is probably

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

with oophagous

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s like in other mackerel shark species. This shark is caught incidentally by

commercial fisheries Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often p ...

, though so infrequently.

Taxonomy and phylogeny

The first known bigeye sand tiger was a female long caught off

Madeira ) , anthem = ( en, "Anthem of the Autonomous Region of Madeira") , song_type = Regional anthem , image_map=EU-Portugal_with_Madeira_circled.svg , map_alt=Location of Madeira , map_caption=Location of Madeira , subdivision_type=Sovereign st ...

in April 1941, on a longline set for

black scabbardfish The black scabbardfish (''Aphanopus carbo'') is a bathypelagic cutlassfish of the family Trichiuridae found in the Atlantic Ocean between latitudes 69°N and 27°N at depths between . Its length is up to , but it reaches maturity around . D ...

(''Aphanopus carbo''). The specimen was

mounted Mount is often used as part of the name of specific mountains, e.g. Mount Everest. Mount or Mounts may also refer to: Places * Mount, Cornwall, a village in Warleggan parish, England * Mount, Perranzabuloe, a hamlet in Perranzabuloe parish, Co ...

and later formed the basis for a

scientific description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have b ...

authored by German

ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish ( Chondrichthyes), and jawless fish ( Agnatha). According to FishBase, 33,400 species of fish had been described as of O ...

Günther Maul Günther Edmund Maul (May 7, 1909 – September 28, 1997) was a German ichthyologist and taxidermist in Portugal. Maul came to Madeira in December 1930 to work as taxidermist at Museu Municipal do Funchal, which opened to the public in 1933. He wa ...

in a 1955 article for ''Notulae Naturae''. He named the species ''noronhai'' in honor of Adolfo César de Noronha, the late Director of the Funchal Museum. Maul assigned his new species to the genus ''

Carcharias ''Carcharias'' is a genus of sand tiger sharks belonging to the family Odontaspididae. Once bearing many prehistoric species, all have gone extinct with the exception of the critically endangered sand tiger shark. Description ''Carcharias'' ar ...

'', which at the time was used for all members of the sand tiger shark family. When the '' Odontaspis'' came to be recognized as a valid genus separate from ''Carcharias'', the bigeye sand tiger was reassigned as well given its resemblance to the smalltooth sand tiger (''O. ferox''). Until more specimens were examined in the 1980s, some authors speculated that this species represented an extreme variant of the smalltooth sand tiger. Other names for this shark include black sand tiger, oceanic sand tiger, and bigeye ragged-tooth shark. Whether the bigeye and smalltooth sand tigers belong in the same family as the superficially similar sand tiger shark (''C. taurus'') has been debated among

systematist Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic tre ...

s, with morphological and

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolo ...

al studies giving inconsistent results. A 2012

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

analysis, based on

mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

, supported a

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

relationship between ''O. noronhai'' and ''O. ferox'' but not a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

consisting of ''Odontaspis'' and ''Carcharias''. Instead, ''Odontaspis'' was found to be closer to the crocodile shark (''Pseudocarcharias kamoharai''), suggesting that it and ''Carcharias'' should be placed in separate families.

Description

With its heavyset body, conical bulbous snout, and large mouth filled with protruding teeth, the bigeye sand tiger looks much like the better-known sand tiger shark. The large eyes lack

s, and behind them are small spiracles. The corner of the mouth extends to behind the level of the eyes, and the jaws are highly protrusible. There are 34–43 upper and 37–46 lower tooth rows; these include zero to two rows of small teeth at the upper symphysis (jaw midpoint) and two to four more rows at the lower symphysis. In each half of the upper jaw, the teeth in the first and second rows are large, those in the third and sometimes fourth rows are small, and those in the rows after are large again. Each tooth has a narrow, awl-like central

cusp A cusp is the most pointed end of a curve. It often refers to cusp (anatomy), a pointed structure on a tooth. Cusp or CUSP may also refer to: Mathematics * Cusp (singularity), a singular point of a curve * Cusp catastrophe, a branch of bifurc ...

flanked by one smaller cusplet on each side; this contrasts with the smalltooth sand tiger, which has two or three lateral cusplets on each side. There are five pairs of

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In co ...

s. The

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 se ...

s are medium-sized and broad with rounded tips. The large first

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 ...

has a rounded apex and is positioned closer to the pectoral than the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two ...

s. The second dorsal fin is about half the size of the first and originates over the rear tips of the pelvic fins. The pelvic fins are almost as large as the first dorsal fin. The

anal 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 see ...

is smaller than the second dorsal fin and positioned behind it. The

caudal peduncle 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 see ...

has a crescent-shaped notch at the dorsal origin of the

caudal 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 se ...

. The lower lobe of the caudal fin is short but distinct, while the upper lobe is long and has a deep notch in the trailing margin near the tip. The skin is covered by overlapping

dermal denticle 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 ...

s, each with three horizontal ridges leading to marginal teeth. This species is plain dark reddish brown to chocolate brown, sometimes with black trailing margins on the fins or a white-tipped first dorsal fin. The eyes are dark orange with vertically oval, green-tinted

pupil The pupil is a black hole located in the center of the Iris (anatomy), iris of the Human eye, eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing ...

s. There are several black patches inside the mouth, such as around the jaws, on the floor of the mouth, and on the

gill arch Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arc ...

es. The largest male and female specimens measured long respectively.

Distribution and habitat

Though extremely rare, the bigeye sand tiger has been reported from scattered locations around the world, suggesting a wide and possibly disjunct global distribution in

tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and warm-

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...

oceanic waters. Most known specimens have come from the Atlantic, where it has been found off Madeira, southern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...

, eastern

Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and ...

, and the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a divergent or constructive plate boundary) located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. In the North Atlantic, the ridge separates the North A ...

. The only evidence for its presence in the Indian Ocean is a set of jaws that may have originated from the

Seychelles Seychelles (, ; ), officially the Republic of Seychelles (french: link=no, République des Seychelles; Creole: ''La Repiblik Sesel''), is an archipelagic state consisting of 115 islands in the Indian Ocean. Its capital and largest city, ...

, though the

South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan and northwestern Ph ...

is another possibility. The existence of this species in the Pacific Ocean was first suspected in 1970 from teeth recovered from bottom

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

s, which was confirmed over a decade later by captures from the

Marshall Islands The Marshall Islands ( mh, Ṃajeḷ), officially the Republic of the Marshall Islands ( mh, Aolepān Aorōkin Ṃajeḷ),'' () is an independent island country and microstate near the Equator in the Pacific Ocean, slightly west of the Inte ...

and

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

. The bigeye sand tiger has been caught between the depths of . Some were recorded over continental and insular shelves, both from near the

sea floor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

and in mid-water. Others were fished from parts of the open ocean that were deep, where they were swimming in the upper levels of the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

. Nighttime captures from relatively shallow depths suggest that this species may make a

diel vertical migration Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The word ''diel'' comes from the Latin ''dies'' day, and means a 24- ...

, rising from the

to the

epipelagic zone The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological proc ...

at night to feed. In Brazilian waters, bigeye sand tigers are only captured in spring, hinting at some type of seasonal migratory movement.

Biology and ecology

One account of a bigeye sand tiger that had been caught alive noted that it behaved very aggressively, thrashing and snapping violently in and out of the water. Its large eyes and uniformly dark coloration are characteristic traits of a mesopelagic fish. The bigeye sand tiger feeds on

es and

. Its reproduction is little-known but probably similar to that of other mackerel sharks, which are

with

s that feed on unfertilized eggs during

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pr ...

( oophagy). Adult females have a single functional

ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...

, on the right, and two functional

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

es. Males mature sexually at somewhere between long, while females mature at around long. No information is available on growth or aging.

Human interactions

Because the bigeye sand tiger is encountered so infrequently, it has no commercial importance. It is caught incidentally on longlines and in

gillnet Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...

s and

purse seine Seine fishing (or seine-haul fishing; ) is a method of fishing that employs a surrounding net, called a seine, that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats. Seine nets can be de ...

s, though the paucity of captures suggest that it mostly lives in waters too deep for

. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

(IUCN) has listed this species as

Data Deficient A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessaril ...

, citing a lack of biological and population data. Since 1997, the

National Marine Fisheries Service The National Marine Fisheries Service (NMFS), informally known as NOAA Fisheries, is a United States federal agency within the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) that is responsible for the stew ...

(NMFS) has prohibited the taking of this species in United States waters.

References

External links

"''Odontaspis noronhai'', Bigeye sand tiger shark" at FishBase

* ttp://shark-references.com/species/view/Odontaspis-noronhai "Species description of ''Odontaspis noronhai''" at Shark-References.com {{Good article bigeye sand tiger Fauna of Madeira Fish of Brazil Fish of Hawaii Taxa named by Günther Maul bigeye sand tiger