Casque (anatomy)

Last updated
Like most hornbills, this male great hornbill has a distinctive casque on its upper mandible. Great hornbill (Buceros bicornis) Photograph by Shantanu Kuveskar.jpg
Like most hornbills, this male great hornbill has a distinctive casque on its upper mandible .
The bony, vascularized casque of the southern cassowary helps the bird to shed excess heat. Casuaris casuaris 2008-11-02 332.JPG
The bony, vascularized casque of the southern cassowary helps the bird to shed excess heat.
The high casque of the veiled chameleon provides an expanded area for the attachment of jaw musculature - and may also help the animal to collect moisture or store fat. Yemen Chameleon.jpg
The high casque of the veiled chameleon provides an expanded area for the attachment of jaw musculature – and may also help the animal to collect moisture or store fat.

A casque is an anatomical feature found in some species of birds, reptiles, and amphibians. In birds, it is an enlargement of the bones of the upper mandible or the skull, either on the front of the face, or the top of the head, or both. The casque has been hypothesized to serve as a visual cue to a bird's sex, state of maturity, or social status; as reinforcement to the beak's structure; or as a resonance chamber, enhancing calls. [4] In addition, they may be used in combat with other members of the same species, in the gathering of food, or in thermoregulation.

Contents

Birds

Structure

Casques are found in a number of species, including most hornbills, all cassowaries, the maleo, the horned guan, the helmeted guineafowl and several species of curassow. [5] In most of these species, the casque is a bony extension of the upper mandible or skull that is covered with a cornified layer of skin. However, in cassowaries, a foamy, elastic layer of collagen sits between the bone and the skin. [5] Hornbill casques grow from an area of vascularized tissue at the front of the skull. [6] In most species, the casque is primarily hollow, with a network of bony filaments at the posterior end. [7] The structure starts small in youngsters and develops over time, and at maturity is typically larger in males than in females. [8] [9] For larger species with larger casques, the growth process may take as long as six years. [10] In general, if male and female casques of a species are similarly sized, then they tend to be differently colored, and if they are similarly colored, they tend to be differently sized. [11] Hornbill species that live in dry, open areas tend to have smaller casques than those that live in forested areas. [12]

Functions

Casques may serve different functions in different species, and may serve multiple functions in a single species. [4] [10] In the hornbills, the casques of males and females of each species differ in size, shape, structure, and color, and the casques of young birds are different than those of adults. [8] These various differences may aid in the recognition of potential mates or competitors. [13] Casques on the bill, particularly those that run the length, or nearly the length, of the culmen , may help to strengthen a long, curved beak, which can allow a stronger bite force at the bill's tip. [8]

Some species use their casques for fighting with other members of the same species. [14] Male helmeted hornbills, for example, clash their casques together in mid-air combats that can last up to two hours. [15] Male great hornbills also bash their casques together, sometimes in aerial combat, sometimes while one of the two birds is perched. [16] Indian grey hornbills casque-butt both in aerial battles, and in clashes between perched and flying birds. While most instances involve two males, clashes can also occur between members of a mated pair. [17]

Heat exchange is a primary function of cassowary casques. Studies have shown that the casques efficiently shed heat at high temperatures and help to restrict heat loss at lower temperatures. Cassowaries have been seen dunking their casques into water when temperatures were high. [1] Some theories that have been advanced in the past for cassowary casques – that they provide a "helmet" to protect the birds' heads as they move through the forest, that they serve as a "shovel" during foraging, or that they are used during fights with conspecifics – have now been largely discounted due to a lack of field observations confirming those uses. [18]

Problems and threats

Casques are regularly subject to injury and disease. Injury can be either self-induced, or caused by conspecifics or environmental factors. Invasive squamous cell carcinoma is a common issue, particularly in the great hornbill. [4] Rhinoceros hornbills and helmeted hornbills have long been hunted for their casques, which are used for carvings. Items made from hornbill ivory date back more than 2000 years in Borneo and more than 1000 years in China. [19] Helmeted hornbills are particularly sought, as their casques are densely solid. Although they are protected by law throughout their range, they are killed at unsustainable rates; between 2011 and 2014, for example, more than 1100 skulls were seized from poachers in Indonesia's Kalimantan region alone. [20]

Reptiles

A number of chameleon species have casques, which in these reptiles are bony protrusions on the top of the head. In species which have casques, males tend to have significantly larger casques than females. [2] Studies have shown that casques are used for communication, including the indication of fighting ability. In some species, the size of the casque accurately predicts the bite strength of the individual. [21] The casques form an attachment point for musculature; bigger casques have a larger area for muscle attachment, which can result in a stronger bite. [2] The veiled chameleon of the arid stretches of southern Saudi Arabia and Yemen has a particularly large casque, which scientists have theorised may be used to collect moisture or store fat. [3]

Casqueheaded lizards in the family Corytophanidae have expanded parietal bones. In the genera Corytophanes and Laemanctus , these modifications are present in both sexes; the thickened bones allow for greater bite strength as there is more area for muscle attachment. This may allow these species to utilize larger prey with more chitinous exoskeletons. In species of the genus Basiliscus , on the other hand, males have much larger parietal crests than females. However, the underlying bones are thin and elongated. Their enlarged crests are used in display; large crests can make the animal appear bigger. Females preferentially choose larger males, and larger males are more successful in aggressive encounters with other males. [22]

See also

Related Research Articles

<span class="mw-page-title-main">Cassowary</span> Genus of flightless birds

Cassowaries are flightless birds of the genus Casuarius in the order Casuariiformes. They are classified as ratites: flightless birds without a keel on their sternum bones. Cassowaries are native to the tropical forests of New Guinea, the Aru Islands (Maluku), and northeastern Australia.

<span class="mw-page-title-main">Hornbill</span> Family of birds

Hornbills are birds found in tropical and subtropical Africa, Asia and Melanesia of the family Bucerotidae. They are characterized by a long, down-curved bill which is frequently brightly coloured and sometimes has a horny casque on the upper mandible. Hornbills have a two-lobed kidney. They are the only birds in which the first and second neck vertebrae are fused together; this probably provides a more stable platform for carrying the bill. The family is omnivorous, feeding on fruit and small animals. They are monogamous breeders nesting in natural cavities in trees and sometimes cliffs. A number of mainly insular species of hornbill with small ranges are threatened with extinction, namely in Southeast Asia.

<i>Buceros</i> Genus of birds

Buceros is a genus of large Asian hornbills.

<span class="mw-page-title-main">Southern ground hornbill</span> Species of bird

The southern ground hornbill is one of two species of ground hornbill, both of which are found solely within Africa, and is the largest species in the hornbill order worldwide. It can be found in the southern regions of Africa, ranging from Kenya to South Africa. Within these regions, they inhabit both woodlands and savannas. The other species of the genus Bucorvus is the Abyssinian ground hornbill, B. abyssinicus.

<span class="mw-page-title-main">African grey hornbill</span> Species of bird

The African grey hornbill is a member of the hornbill family of mainly tropical near-passerine birds found in the Old World. It is a widespread resident breeder in much of sub-Saharan Africa and the southwest of the Arabian Peninsula. The African grey hornbill has escaped or been deliberately released into Florida, USA, but there is no evidence that the population is breeding and may only persist due to continuing releases or escapes.

<span class="mw-page-title-main">Malabar grey hornbill</span> Species of bird

The Malabar gray hornbill is a hornbill endemic to the Western Ghats and associated hills of southern India. They have a large beak but lack the casque that is prominent in some other hornbill species. They are found mainly in dense forest and around rubber, arecanut or coffee plantations. They move around in pairs or small groups, feeding on figs and other forest fruits. Their loud cackling and laughing call makes them familiar to people living in the region.

<i>Corythosaurus</i> Extinct genus of dinosaurs

Corythosaurus is a genus of hadrosaurid "duck-billed" dinosaur from the Late Cretaceous period, about 77–75.7 million years ago, in what is now western North America. Its name is derived from the Greek word κόρυς, meaning "helmet", named and described in 1914 by Barnum Brown. Corythosaurus is now thought to be a lambeosaurine, thus related to Lambeosaurus, Nipponosaurus, Velafrons, Hypacrosaurus, and Olorotitan. Corythosaurus has an estimated length of 7.7–9 metres (25–30 ft) and has a skull, including the crest, that is 70.8 centimetres tall.

<span class="mw-page-title-main">Southern cassowary</span> Species of bird

The southern cassowary, also known as double-wattled cassowary, Australian cassowary, or two-wattled cassowary, is a large flightless black bird, found in Indonesia, Papua New Guinea, and northeastern Australia. It is one of the three living species of cassowary, alongside the dwarf cassowary and the northern cassowary. It is a ratite and therefore related to the emu, ostriches, rheas and kiwi.

<span class="mw-page-title-main">Rhinoceros hornbill</span> Species of bird

The rhinoceros hornbill is a large species of forest hornbill (Bucerotidae). In captivity it can live for up to 35 years. It is found in lowland and montane, tropical and subtropical climates and in mountain rain forests up to 1,400 metres in Borneo, Sumatra, Java, the Malay Peninsula, Singapore, and southern Thailand.

<span class="mw-page-title-main">Hornbill ivory</span> Material derived from hornbills beak

Hornbill ivory is a precious ornamental material derived from the helmeted hornbill, a large bird of the Malay Peninsula, Sumatra, and Borneo.

<span class="mw-page-title-main">Helmeted hornbill</span> Species of bird

The helmeted hornbill is a very large bird in the hornbill family. It is found on the Malay Peninsula, Sumatra, Borneo, Thailand and Myanmar. The casque accounts for some 11% of its 3 kg weight. Unlike any other hornbill, the casque is almost solid, and is used in head-to-head combat among males. It is a belief among the Punan Bah that a large helmeted hornbill guards the river between life and death.

<span class="mw-page-title-main">Casuariiformes</span> Order of birds

The Casuariiformes is an order of large flightless birds that has four surviving members: the three species of cassowary, and the only remaining species of emu. They are divided into either a single family, Casuariidae, or more typically two, with the emu splitting off into its own family, Dromaiidae.

<span class="mw-page-title-main">Great hornbill</span> Bird species

The great hornbill, also known as the concave-casqued hornbill, great Indian hornbill or great pied hornbill, is one of the larger members of the hornbill family. It occurs in the Indian subcontinent and Southeast Asia. It is predominantly frugivorous, but also preys on small mammals, reptiles and birds. It has been listed as Vulnerable on the IUCN Red List since 2018. It is known to have lived for nearly 50 years in captivity. Due to its large size and colour, and importance in many tribal cultures and rituals, the Government of Kerala declared it as the official Kerala state bird.

<span class="mw-page-title-main">Dwarf cassowary</span> Species of bird

The dwarf cassowary, also known as Bennett's cassowary, little cassowary, mountain cassowary or muruk, is the smallest of the three extant species of cassowaries.

<span class="mw-page-title-main">Northern cassowary</span> Species of bird

The northern cassowary, also known as the one-wattled cassowary, single-wattled cassowary, or golden-necked cassowary, is a large, stocky flightless bird of northern New Guinea. It is one of the three living species of cassowary, alongside the dwarf cassowary and the southern cassowary. It is a member of the superorder Paleognathae.

<span class="mw-page-title-main">Cape dwarf chameleon</span> Species of reptile

The Cape dwarf chameleon is a chameleon native to the South African province of the Western Cape, where it is restricted to the region around Cape Town.

<span class="mw-page-title-main">Wreathed hornbill</span> Species of bird

The wreathed hornbill is an Old World tropical bird of the hornbill family Bucerotidae, also called bar-pouched wreathed hornbill due to its distinctive blue-black band on its lower throat sac. It is named after its characteristic long, curved bill that develops ridges, or wreaths, on the casque of the upper mandible in adults. Males are black with a rufous crown, a white upper breast and face, and a yellow featherless throat. Females are uniformly black with a blue throat and are slightly smaller than males.

<span class="mw-page-title-main">Wattle (anatomy)</span> Fleshy growth on the head or neck of a bird

A wattle is a fleshy caruncle hanging from various parts of the head or neck in several groups of birds and mammals. Caruncles in birds include those found on the face, wattles, dewlaps, snoods, and earlobes. Wattles are generally paired structures but may occur as a single structure when it is sometimes known as a dewlap. Wattles are frequently organs of sexual dimorphism. In some birds, caruncles are erectile tissue and may or may not have a feather covering.

<i>Trioceros hoehnelii</i> Species of lizard

Trioceros hoehnelii, commonly known as von Höhnel's chameleon, the helmeted chameleon, and the high-casqued chameleon, is a species of chameleon, a lizard in the family Chamaeleonidae. The species is native to eastern Africa.

<i>Corythoraptor</i> Extinct genus of dinosaurs

Corythoraptor is a genus of oviraptorid dinosaur from the late Maastrichtian Nanxiong Formation of South China. It contains one species, C. jacobsi, known from a single well-preserved skeleton, and named after paleontologist Louis L. Jacobs. It bears a tall crest similar to that of the modern cassowary, and possibly had a similar functionality of display and resonance to detect lower-frequency sounds.

References

Citations

Sources