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

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), ...

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 g ...

in the

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 ...

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. Most ...

s, and a capacious mouth with the narrow teeth prominently exposed. It can be distinguished from the similar

smalltooth sand tiger The smalltooth sand tiger or bumpytail ragged-tooth (''Odontaspis ferox'') is a species of Lamniformes, mackerel shark in the family (biology), family Sand shark, Odontaspididae, with a patchy but worldwide distribution in tropical and warm tempe ...

(''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 marg ...

s and oceanic waters at depths of , the bigeye sand tiger may make vertical and horizontal migratory movements. It feeds on

bony fish 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 ...

es and

squid A squid (: squid) is a mollusc with an elongated soft body, large eyes, eight cephalopod limb, arms, and two tentacles in the orders Myopsida, Oegopsida, and Bathyteuthida (though many other molluscs within the broader Neocoleoidea are also ...

, 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 ...

. Reproduction is probably

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

with

oophagous Oophagy ( ) or ovophagy, literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek (, "egg") and classical Greek (, "to ...

embryo An embryo ( ) is the initial stage of development for 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 sp ...

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 Madeira ( ; ), officially the Autonomous Region of Madeira (), is an autonomous Regions of Portugal, autonomous region of Portugal. It is an archipelago situated in the North Atlantic Ocean, in the region of Macaronesia, just under north of ...

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 . De ...

(''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 scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it diffe ...

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, 35,800 species of fish had been described as of March 2 ...

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 w ...

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'', also known as sand tiger sharks, is a genus of mackerel sharks belonging to the family Carchariidae, of which it is the only extant member. Once bearing many prehistoric species, all have gone extinct with the exception of the cri ...

'', which at the time was used for all members of the sand tiger shark family. When the ''

Odontaspis ''Odontaspis'' (from 'tooth') and 'shield') is a genus of sand shark with two extant species. Description Bigeye sand tigers can reach a length of about and smalltooth sand tigers of about 4.1 m. They are large-bodied sharks with l ...

'' came to be recognized as a valid genus separate from ''Carcharias'', the bigeye sand tiger was reassigned as well given its resemblance to the

(''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 The sand tiger shark (''Carcharias taurus''), grey/gray nurse shark (in Australia), spotted ragged-tooth shark (in South Africa), or blue-nurse sand tiger, is a species of shark that inhabits subtropical and temperate waters worldwide. It inhabit ...

(''C. taurus'') has been debated among

systematist 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: phylogenetic trees, phylogenies). Phyl ...

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-physiology ...

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 and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the 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 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 ...

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 row Sharks continually shed their teeth; some Carcharhiniformes shed approximately 35,000 teeth in a lifetime, replacing those that fall out. There are four basic types of shark teeth: dense flattened, needle-like, pointed lower with triangular upp ...

s; 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 bifu ...

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 c ...

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

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

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 (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 ...

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 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 ...

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

caudal peduncle 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 only ...

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

caudal 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 only ...

. 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 scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

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 hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black becau ...

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 paired bony/ cartilaginous "loops" behind the throat ( pharyngeal cavity) of fish, which support the fish gills. As chordates, all vertebrate embryos develop pharyngeal arches, though the event ...

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, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

and warm-

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

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

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

, eastern

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

, and the

Mid-Atlantic Ridge The Mid-Atlantic Ridge is a mid-ocean ridge (a Divergent boundary, divergent or constructive Plate tectonics, plate boundary) located along the floor of the Atlantic Ocean, and part of the List of longest mountain chains on Earth, longest mountai ...

. 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 (; Seychellois Creole: ), is an island country and archipelagic state consisting of 155 islands (as per the Constitution) in the Indian Ocean. Its capital and largest city, Victoria, ...

, 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 South China, in the west by the Indochinese Peninsula, in the east by the islands of Taiwan island, Taiwan and northwestern Philippines (mainly Luz ...

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 solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

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

Marshall Islands The Marshall Islands, officially the Republic of the Marshall Islands, is an island country west of the International Date Line and north of the equator in the Micronesia region of the Northwestern Pacific Ocean. The territory consists of 29 c ...

and

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

. 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 The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity, light penetration) and chemical ( pH, dissolved oxygen, nutrient salts) characteristics of seawater at different depths for a defined ...

. 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 adjective "diel" ( IPA: , ) comes from , and refers to a 24-hour ...

, rising from the

to the

epipelagic zone The photic zone (or 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 ...

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 pregn ...

(

oophagy Oophagy ( ) or ovophagy, literally "egg eating", is the practice of embryos feeding on eggs produced by the ovary while still inside the mother's uterus. The word oophagy is formed from the classical Greek (, "egg") and classical Greek (, "to ...

). Adult females have a single functional

ovary The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/ oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are end ...

, on the right, and two functional

uterus The uterus (from Latin ''uterus'', : uteri or uteruses) or womb () is the hollow organ, organ in the reproductive system of most female mammals, including humans, that accommodates the embryonic development, embryonic and prenatal development, f ...

es. Males

mature sexually Sexual maturity is the capability of an organism to reproduce. In humans, it is related to both puberty and adulthood. ''Puberty'' is the biological process of sexual maturation, while ''adulthood'', the condition of being socially recognized as ...

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) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

(IUCN) has listed this species as

Least Concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...

. 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 ste ...

(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 The bigeye sand tiger (''Odontaspis noronhai'') is an extremely rare species of Lamniformes, mackerel shark in the family (biology), family Sand shark, Odontaspididae, with a possible worldwide distribution. A large, bulky species reaching at lea ...

Fauna of Madeira Marine fish of Brazil Fish of Hawaii Taxa named by Günther Maul