Premaxilla

The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla and usually termed as the incisive bone. Other terms used for this structure include premaxillary bone or os premaxillare, and intermaxillary bone or os intermaxillare.

Premaxilla
Spinosaurus skull en
Skull of Spinosaurus aegyptiacus, premaxilla in orange
Gray199
Human premaxilla and its sutures
Details
Precursormedian nasal prominence
Anatomical terminology

Human anatomy

In humans, the premaxilla is referred to as the incisive bone and is the part of the maxilla which bears the incisor teeth, and encompasses the anterior nasal spine and alar region. In the nasal cavity, the premaxillary element projects higher than the maxillary element behind. The palatal portion of the premaxilla is a bony plate with a generally transverse orientation. The incisive foramen is bound anteriorly and laterally by the premaxilla and posteriorly by the palatine process of the maxilla. [1]

Embryology

In the embryo, the nasal region develops from neural crest cells which start their migration down to the face during the fourth week of gestation. A pair of symmetrical nasal placodes (thickenings in the epithelium) are each divided into medial and lateral processes by the nasal pits. The medial processes become the septum, philtrum, and premaxilla.[2]

The first ossification centers in the area of the future premaxilla appear during the seventh week above the germ of the second incisor on the outer surface of the nasal capsule. After eleven weeks an accessory ossification center develops into the alar region of the premaxilla. Then a premaxillary process grow upwards to fuse with the frontal process of the maxilla; and later expands posteriorly to fuse with the alveolar process of the maxilla. The boundary between the premaxilla and the maxilla remains discernible after birth and a suture is often observable up to five years of age. [1]

In bilateral cleft lip and palate, the growth pattern of the premaxilla differs significantly from the normal case; in utero growth is excessive and directed more horizontally, resulting in a protrusive premaxilla at birth.[3]

Evolutionary variation

Forming the oral edge of the upper jaw in most jawed vertebrates, the premaxillary bones comprise only the central part in more primitive forms. They are fused in blowfishes and absent in cartilaginous fishes such as sturgeons.[4]

Reptiles and most non-mammalian therapsids have a large, paired, intramembranous bone behind the premaxilla called the septomaxilla. Because this bone is vestigial in Acristatherium (a Cretaceous eutherian) this species is believed to be the oldest known therian mammal. Intriguingly the septomaxilla is still present in monotremes.[5][6]

The differences in the size and composition in the premaxilla of various families of bats is used for classification.[7]

References

  1. ^ a b Lang, Johannes (1995). Clinical anatomy of the masticatory apparatus peripharyngeal spaces. Thieme. ISBN 978-3-13-799101-4.
  2. ^ "Nasal Anatomy". Medscape. June 2011. Retrieved 3 December 2011.
  3. ^ Vergervik, Karin (1983). "Growth Characteristics of the Premaxilla and Orthodontic Treatment Principles in Bilateral Cleft Lip and Palate" (PDF). Cleft Palate Journal. 20 (4). Retrieved 3 December 2011.
  4. ^ "Premaxilla". ZipCodeZoo. Retrieved 3 December 2011.
  5. ^ Hu, Yaoming; Meng, Jin; Li, Chuankui; Wang, Yuanqing (January 22, 2010). "New basal eutherian mammal from the Early Cretaceous Jehol biota, Liaoning, China". Proc Biol Sci. 277 (1679): 229–236. doi:10.1098/rspb.2009.0203. PMC 2842663. PMID 19419990.
  6. ^ Wible, John R.; Miao, Desui; Hopson, James A. (March 1990). "The septomaxilla of fossil and recent synapsids and the problem of the septomaxilla of monotremes and armadillos". Zoological Journal of the Linnean Society. 98 (3): 203–228. doi:10.1111/j.1096-3642.1990.tb01207.x.
  7. ^ Myers, P.; Espinosa, R.; Parr, C. S.; Jones, T.; Hammond, G. S.; Dewey, T. A. (2006). "Premaxillae of bats". Animal Diversity Web. Retrieved 3 December 2011.
Acanthomorpha

This article is about a group of ray-finned fish called Acanthomorpha or acanthomorphs. Acanthomorph is also a descriptive name for a spiny-walled subgroup of the microscopic fossils called acritarchs.

Acanthomorpha (meaning "thorn-shaped" in Greek) is an extraordinarily diverse taxon of teleost fishes with spiny-rays. The clade contains about one third of the world's modern species of vertebrates: over 14,000 species.A key anatomical innovation in acanthomorphs is hollow and unsegmented spines at the anterior edge of the dorsal and anal fins. A fish can extend these sharp bony spines to protect itself from predators, but can also retract them to decrease drag when swimming. Another shared feature is a particular rostral cartilage, associated with ligaments attached to the rostrum and premaxilla, that enables the fish to protrude its jaws considerably to catch food.Rosen coined the name in 1973 to describe a clade comprising Acanthopterygii, Paracanthopterygii, and also ctenothrissiform fossils from the Cretaceous Period, such as Aulolepis and Ctenothrissa. Those fossils share several details of the skeleton, and especially of the skull, with modern acanthomorphs. Originally based on anatomy, Acanthomorpha has been borne out by more recent molecular analyses.

Archosauromorpha

Archosauromorpha (Greek for "ruling lizard forms") is a clade of diapsid reptiles containing all reptiles more closely related to archosaurs (such as crocodilians and dinosaurs, including birds) rather than lepidosaurs (such as tuataras, lizards, and snakes). Archosauromorphs first appeared during the middle Permian, though they became much more common and diverse during the Triassic period.Although Archosauromorpha was first named in 1946, its membership did not become well-established until the 1980s. Currently Archosauromorpha encompasses four main groups of reptiles: the stocky, herbivorous allokotosaurs and rhynchosaurs, the hugely diverse Archosauriformes, and a polyphyletic grouping of various long-necked reptiles including Protorosaurus, tanystropheids, and Prolacerta. Other groups including pantestudines (turtles and their extinct relatives) and the semiaquatic choristoderes have also been placed in Archosauromorpha by some authors.

Archosauromorpha is one of the most diverse groups of reptiles, but its members can be united by several shared skeletal characteristics. These include laminae on the vertebrae, a posterodorsal process of the premaxilla, a lack of notochordal canals, and the loss of the entepicondylar foramen of the humerus.

Caiman venezuelensis

Caiman venezuelensis is an extinct species of caiman that lived in South America during the Pleistocene. The holotype of C. venezuelensis — OR-1677, a partial left premaxilla bone — was discovered in the locality of El Breal of Orocual, in the Mesa Formation, in the state of Monagas, Venezuela, the country of which derives their species name.Cidade et al. (2019) rejected the classification of C. venezuelensis as a distinct species, and considered it to be a junior synonym of extant spectacled caiman (Caiman crocodilus).

Chiappeavis

Chiappeavis is a genus of enantiornithean bird from Early Cretaceous of northeastern China. The only species is Chiappeavis magnapremaxillo. Chiappeavis is classified within the family Pengornithidae. It is known from a single, almost complete skeleton including feather impressions discovered in the Jiufotang Formation of the Jehol Group. Long feathers formed a fan-shaped tail that was probably employed in flight.The genus name honors Luis Chiappe for his extensive research on Mesozoic birds. The specific name magnapremaxillo ("large premaxilla") alludes to the unusually large size of the premaxillary bone, the frontmost bone of the upper jaw.The only specimen (holotype, STM29-11), of a subadult individual, was discovered on a single slab in Jianchang County, Liaoning. Is housed in the Shandong Tianyu Museum of Nature in Pingyi County, Shandong.

Dental alveolus

Dental alveoli (singular alveolus) are sockets in the jaws in which the roots of teeth are held in the alveolar process with the periodontal ligament. The lay term for dental alveoli is tooth sockets. A joint that connects the roots of the teeth and the alveolus is called gomphosis (plural gomphoses). Alveolar bone is the bone that surrounds the roots of the teeth forming bone sockets.

In mammals, tooth sockets are found in the maxilla, the premaxilla, and the mandible.

Iberosuchus

Iberosuchus (meaning "Iberian crocodile") is a genus of extinct sebecosuchian mesoeucrocodylian found in Western Europe from the Eocene. Remains from Portugal was described in 1975 by Antunes as a sebecosuchian crocodilian. This genus has one species: I. macrodon (meaning "large toothed). Iberosuchus was a carnivore, unlike the crocodilians today, they are not aquatic and are instead terrestrial.

First of its fossils were cranial remains found in Portugal, and later more fossils were found in France and Spain. They are only known from very fragmentary fossils, elements of the skull, dentary, teeth and osteoderm.

Incisive bone

In human anatomy, the incisive bone or (Latin) os incisivum is the portion of the maxilla adjacent to the incisors. It is formed from the fusion of a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals. While Johann Wolfgang von Goethe was not the first one to discover incisive bone in the humans, he was the first to prove its presence across mammals. Hence, incisive bone is also known as Goethe's bone

In other animals the term premaxilla is more often used to refer to the incisive bone. Yet other terms include premaxillary bone, os premaxillare, intermaxillary bone, and os intermaxillare.

Incisor

Incisors (from Latin incidere, "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whereas armadillos have none.

Kansajsuchus

Kansajsuchus is an extinct genus of goniopholidid mesoeucrocodylian. It is based on PIN 2399/301, a right premaxilla, one of the bones of the tip of the snout. This specimen was found in rocks of the lower Santonian-age Upper Cretaceous Yalovach Svita of Kansai, in the Fergana Basin of Tajikistan. Additional fossils including vertebrae and bony armor have been assigned to this genus. It would have been a large animal, estimated at up to 8 metres (26 ft) long. Kansajsuchus was described in 1975 by Mikhail Efimov. The type species is Kansajsuchus extensus.

Halliday et al. (2013) confirmed the validity of the species K. extensus, and its phylogenetic position among other basal goniopholidids from Asia. "Sunosuchus" shartegensis was found to represent its sister taxon, and both species were placed in a distinct lineage from the type species of Sunosuchus, S. miaoi, however with a weak support. Therefore, the authors raised the suggestion that later revisions and phylogenetic analyses would result in the abandonment of the name Kansajsuchus, and a referral of its type species to Sunosuchus. However, a subsequent paper by Kuzmin et al. (2019) showed that Kansajsuchus is a member of the family Paralligatoridae.

Kileskus

Kileskus (meaning lizard in the Khakas language) is a genus of tyrannosauroid dinosaur known from partial remains found in Middle Jurassic (Bathonian stage) Itat Formation of Krasnoyarsk Krai, Russia. Fossils recovered include the holotype maxilla, a premaxilla, a surangular, and a few bones from the hand and foot. The skull bones are similar to those of Proceratosaurus. The type species is K. aristotocus. Kileskus was named in 2010 by Averianov and colleagues.

Makaracetus

Makaracetus is an extinct protocetid early whale the remains of which were found in 2004 in Lutetian layers of the Domanda Formation in the Sulaiman Range of Balochistan, Pakistan (30.1°N 69.8°E / 30.1; 69.8, paleocoordinates 11.7°N 65.0°E / 11.7; 65.0).Makaracetus is unique among archaeocetes in its feeding adaptations; its proboscis and the hypertrophied facial muscles. The genus was adequately named after Makara, a Hindu mythological animal, half-mammal (often an elephant), half-fish, and cetus, Latin for "whale". The species name, bidens, is Latin for "two-teeth", in reference to the retention of only two incisors in each premaxilla. Makaracetus' unique features even lead Gingerich et al. 2005 to propose a new classification of Protocidae based on the degree of their aquatic adaptation; with Makarcetus alone in the subfamily Makaracetinae.A combination of cranial features indicate that Makaracetus had a short, muscular proboscis similar to a tapir. There are broad and shallow narial grooves on the dorsal side of the premaxilla extending the nasal vestibule to the anterior end of the rostrum. These grooves are paralleled on the ventral side by extraordinary lateral fossae, stretching from the anterior maxilla and over the premaxilla. The rostrum is angled downwards, like in a dugong, and has a reduced number of incisors. Enlarged foramina in front of the orbits indicate that the rostrum had a rich blood supply.No living mammal displays this combination of characteristics. The expanded nasal is present in tapirs, but they are not aquatic animals. The morphology of sirenian rostra is similar, but sirenians are herbivorous whereas Makaracetus' dentition clearly indicate that it was carnivorous. Walrus cranial morphology is different, but they are aquatic and use specialized buccal and facial muscles to feed on mollusks, fossils of which are abundant in the Domanda Formation, and they probably provide the best ecological model among living mammals. More complete fossils must be recovered before Makaracetus can be adequately described.

Mosaiceratops

Mosaiceratops is a genus of ceratopsian described by Zheng, Jin & Xu in 2015 found in the Xiaguan Formation of Neixiang County. Although phylogenetic analysis have found it to be the most basal neoceratopsian, the authors noted that several features in the premaxilla and nasal bones are shared with the family Psittacosauridae, indicating that neoceratopsians evolved premaxillary teeth twice and that Psittacosauridae is not a primitive family as previously thought.

Peirosaurus

Peirosaurus is an extinct genus of peirosaurid crocodylomorph known from the Late Cretaceous period (late Maastrichtian stage) of Minas Gerais, southern Brazil. It contains a single species, Peirosaurus torminni. It is the type genus of the family Peirosauridae.

Shuangbaisaurus

Shuangbaisaurus (meaning "Shuangbai reptile") is an extinct genus of theropod dinosaur, possibly a dilophosaurid, that lived in the Early Jurassic of Yunnan Province, China. It contains a single species, S. anlongbaoensis, represented by a partial skull. Like the theropods Dilophosaurus and Sinosaurus, the latter of which was its contemporary, Shuangbaisaurus bore a pair of thin, midline crests on its skull. Unusually, these crests extended backwards over the level of the eyes, which, along with the unusual orientation of the jugal bone, led the describers to name it as a new genus. However, Shuangbaisaurus also possesses a groove between its premaxilla and maxilla, a characteristic which has been used to characterize Sinosaurus as a genus. Among the two morphotypes present within the genus Sinosaurus, Shuangbaisaurus more closely resembles the morphotype that is variably treated as a distinct species, S. sinensis, in its relatively tall skull.

Skull roof

The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium.

In comparative anatomy the term is used on the full dermatocranium. In general anatomy, the roofing bones may refer specifically to the bones that form above and alongside the brain and neurocranium (i.e., excluding the marginal upper jaw bones such as the maxilla and premaxilla), and in human anatomy, the skull roof often refers specifically to the skullcap.

Tanycolagreus

Tanycolagreus is a genus of coelurosaurian theropod from the Late Jurassic of North America.

Teleost

The teleosts or Teleostei (Greek: teleios, "complete" + osteon, "bone") are by far the largest infraclass in the class Actinopterygii, the ray-finned fishes, and make up 96% of all extant species of fish. Teleosts are arranged into about 40 orders and 448 families. Over 26,000 species have been described. Teleosts range from giant oarfish measuring 7.6 m (25 ft) or more, and ocean sunfish weighing over 2 t (2.0 long tons; 2.2 short tons), to the minute male anglerfish Photocorynus spiniceps, just 6.2 mm (0.24 in) long. Including not only torpedo-shaped fish built for speed, teleosts can be flattened vertically or horizontally, be elongated cylinders or take specialised shapes as in anglerfish and seahorses. Teleosts dominate the seas from pole to pole and inhabit the ocean depths, estuaries, rivers, lakes and even swamps.

The difference between teleosts and other bony fish lies mainly in their jaw bones; teleosts have a movable premaxilla and corresponding modifications in the jaw musculature which make it possible for them to protrude their jaws outwards from the mouth. This is of great advantage, enabling them to grab prey and draw it into the mouth. In more derived teleosts, the enlarged premaxilla is the main tooth-bearing bone, and the maxilla, which is attached to the lower jaw, acts as a lever, pushing and pulling the premaxilla as the mouth is opened and closed. Other bones further back in the mouth serve to grind and swallow food. Another difference is that the upper and lower lobes of the tail (caudal) fin are about equal in size. The spine ends at the caudal peduncle, distinguishing this group from other fish in which the spine extends into the upper lobe of the tail fin.

Teleosts have adopted a range of reproductive strategies. Most use external fertilisation: the female lays a batch of eggs, the male fertilises them and the larvae develop without any further parental involvement. A fair proportion of teleosts are sequential hermaphrodites, starting life as females and transitioning to males at some stage, with a few species reversing this process. A small percentage of teleosts are viviparous and some provide parental care with typically the male fish guarding a nest and fanning the eggs to keep them well-oxygenated.

Teleosts are economically important to humans, as is shown by their depiction in art over the centuries. The fishing industry harvests them for food, and anglers attempt to capture them for sport. Some species are farmed commercially, and this method of production is likely to be increasingly important in the future. Others are kept in aquariums or used in research, especially in the fields of genetics and developmental biology.

Trilophosauridae

Trilophosaurs are lizard-like Triassic allokotosaur reptiles related to the archosaurs. The best known genus is Trilophosaurus, a herbivore up to 2.5 metres (8.2 feet) long. It had a short, unusually heavily built skull, equipped with massive, broad flattened cheek teeth with sharp shearing surfaces for cutting up tough plant material. Teeth are absent from the premaxilla and front of the lower jaw, which in life were probably equipped with a horny beak.

The skull is also unusual in that the lower temporal opening is missing, giving the appearance of a euryapsid skull, and originally the Trilophosaurs were classified with placodonts and sauropterygia. Carroll (1988) suggests that the lower opening may have been lost to strengthen the skull.Trilophosaurs are so far known only from the Late Triassic of North America and Europe.

Below is a cladogram showing the phylogenetic relationships of Trilophosauridae within Archosauromorpha as recovered by Nesbitt et al. (2015).

Wargosuchus

Wargosuchus (meaning "warg crocodile") is an extinct genus of baurusuchid mesoeucrocodylian from the Late Cretaceous of Argentina. It is known from a fragmentary skull from the Santonian-age Bajo de la Carpa Formation of the Neuquén Group, found in the vicinity of Neuquén, Neuquén Province, and was described by Agustín Martinelli and Diego Pais in 2008. The type species, and so far the only species, is Wargosuchus australis.Wargosuchus is based on MOZ-PV 6134, a partial right premaxilla and maxilla, and partial skull roof. Martinelli and Pais distinguished Wargosuchus from other mesoeucrocodylians by skull details, such as a deep groove on the midline of the frontal bones, a large depression for the olfactory bulbs, and enlargement of the last tooth of the premaxilla followed by a deep pit for the following tooth of the lower jaw. The animal had a robust skull. It shared its setting with four other taxa of mesoeucrocodylians: common Notosuchus, and rare Cynodontosuchus, Lomasuchus, and Gasparinisuchus.

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