''Sphyrna alleni'', the shovelbill shark, is a species of

hammerhead shark The hammerhead sharks are a group of sharks that form the family Sphyrnidae, named for the unusual and distinctive form of their heads, which are flattened and laterally extended into a Hammerhead shark#Cephalofoil, cephalofoil (a T-shape or " ...

found along the West Atlantic coast from

Belize Belize is a country on the north-eastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a maritime boundary with Honduras to the southeast. P ...

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 ...

. Its pointed cephalofoil distinguishes it from the more northern

bonnethead shark The bonnethead (''Sphyrna tiburo''), also called a bonnet shark or shovelhead, is a small member of the hammerhead shark genus ''Sphyrna'', and part of the family Sphyrnidae. It is an abundant species in the littoral zone of the North Atlantic a ...

(''Sphyrna tiburo''), from which it was split in 2024. The species is also diagnosed by different tooth and precaudal vertebrae counts.

Etymology

The species is named after

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

co-founder

Paul Allen Paul Gardner Allen (January 21, 1953 – October 15, 2018) was an American businessman, computer programmer, and investor. He co-founded Microsoft, Microsoft Corporation with his childhood friend Bill Gates in 1975, which was followed by the ...

. The Paul G. Allen Family Foundation funded the research efforts that led to the discovery of the species. The common name of "shovelbill shark" corresponds to the name used for the shark in

, where the holotype was discovered.

Discovery

A 2012 study of the

mitochondrial A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

gene NADH2 across

elasmobranchs Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by ha ...

compared bonnethead shark specimens from the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

and

Trinidad Trinidad is the larger, more populous island of the Republic of Trinidad and Tobago, the country. The island lies off the northeastern coast of Venezuela and sits on the continental shelf of South America. It is the southernmost island in ...

, and found that the two groups clustered separately, and that ''Sphyrna tiburo'' was likely a species complex. The southern lineage was provisionally referred to as ''Sphyrna'' cf. ''tiburo'', although the authors noted that imprecision in the type locality of ''S. tiburo'' could affect the nomenclature. Between 2016 and 2019, twelve specimens of bonnethead sharks characterized by a pointed, shovel-shaped cephalofoil were captured by anglers in Belize and sent to researchers, who studied both the DNA and physical characteristics of the sharks. Prior to that, a 2015 study of bonnethead sharks in

Panama Panama, officially the Republic of Panama, is a country in Latin America at the southern end of Central America, bordering South America. It is bordered by Costa Rica to the west, Colombia to the southeast, the Caribbean Sea to the north, and ...

had already found evidence of multiple species possibly existing. In 2021, analysis of populations from Southeastern Brazil connected them to the Caribbean lineage, although genetic differentiation indicated that declining Brazilian populations were not being replenished by Caribbean individuals.

Description

''Sphyrna alleni'' is a small species of shark, measuring less than in length. Like other

s, its head is shaped into a flattened cephalofoil. The latter has a more angular anterior edge than that of ''S. tiburo'', and bears lobes on its posterior edges, leading to it being described as "shovel-like". In males, the cephalofoil bears an additional bulge on its anterior side. The teeth are sharper and pointier than in ''S. tiburo''. Individuals possess 80 to 83 precaudal vertebrae, around 10 more than in ''S. tiburo''.

Phylogeny

A 2016

molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleot ...

study placed the divergence between bonnethead shark lineages in Belize and North America around 3.61 to 5.62 Mya. Due to similarity in cephalofoil shapes between ''Sphyrna alleni'' and ''Sphyrna tiburo vespertina'', it has been proposed that the two could represent sister lineages, having diverged from each other later following the closure of the

Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...

Distribution and ecology

The species is distributed on the West Atlantic coast from

. No geographical barrier separates it from the bonnethead shark further north, and a

contact zone In ethnography, a contact zone is a conceptual space where different cultures interact. In a 1991 keynote address to the Modern Language Association titled "Arts of the Contact Zone", Mary Louise Pratt introduced the concept, saying "I use this ...

has been proposed to range from

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

to Belize. Shovelbill sharks are predators.

Conservation

As the populations of ''Sphyrna alleni'' are comparatively less well-managed than those of ''S. tiburo'' further north, the former has been described by its discoverers as "warrant nga highly threatened status". Threats included

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing Fish stocks, fish stock), resu ...

, with the shark being frequently caught by anglers. Actions taken by

to limit the threat to shark populations, such as a ban on

gillnets 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 ...

and the establishment of protected areas, have been stated by Demian Chapman to potentially help the species.

References

Works cited

* * {{Taxonbar, from=Q130357373 alleni Taxa named by Cindy Gonzalez Taxa named by Bautisse Postaire Taxa named by William Driggers Taxa named by Susana Caballero Taxa named by Demian Chapman Fish described in 2024