Hunter-Schreger band

Last updated

Hunter-Schreger bands, commonly abbreviated as HSB, are features of the enamel of the teeth in mammals, mostly placentals. [1] In HSB, enamel prisms are arranged in layers of varying thickness at about right angles to each other. HSB strengthen the enamel and prevent cracks from propagating through the tooth. [2]

Contents

Evolution

HSB are first observed in early Paleocene mammals, but at this time the HSB occupy only a small portion of the incisor and the angle between the bands is low. By the late Paleocene, HSB is seen to extend throughout the enamel and the bands are located at nearly right angles to each other. [1] Under oblique reflected light HSB can be seen as dark and light strips of variable width.

Glires

Among Glires, the group containing rodents, lagomorphs, and their primitive relatives, the absence of HSB from the incisors has been considered primitive. [3] Some early representatives, including Eurymylus , lack HSB, but others, including Matutinia [4] and some mimotonids, have double-layered incisor enamel with HSB in the inner portion (portio interna, PI). Other mimotonids have single-layered enamel with HSB. All leporids studied also exhibit this pattern, except for an early Eocene, indeterminate leporid with HSB only in the PI. [5] Ochotonids also have HSB in the PI only. [6]

In rodents, HSB are usually present in the PI. Three types of HSB can be separated—pauciserial, uniserial, and multiserial. Pauciserial HSB, present in some primitive Paleogene rodents, are usually three to six prisms thick and have inter-prismatic matrix (IPM) surrounding the prisms, which have irregular cross-sections. Uniserial HSB, present in most living rodents, consist of a single layer of prisms. Multiserial HSB, three to seven prisms thick, characterize the living Hystricognathi and the gundis (Ctenodactylidae) and springhares (Pedetes). [2] There are three subtypes on the basis of the orientation of the IPM. In the first, the IPM runs mostly parallel to the HSB, but does not surround it as in pauciserial enamel; in the second, the IPM makes an angle of about 45° with the HSB; and in the third, the two are located at right angles to each other. The last type serves to further strengthen the enamel and is characteristic of the Octodontoidea. [7]

Carnivorans

Among carnivorans, the hyenas exhibit specialized HSB, which form a complex, three-dimensional zigzag pattern, a specialization for bone-eating. [8]

The teeth of Arctodus pristinus transition between undulating to acute-angled Hunter-Schreger bands while Arctodus simus exhibited a transition between undulating to zigzag bands, demonstrating an evolution towards reinforced tooth enamel. This has been convergently evolved with giant pandas, agriotheriin bears, and Hemicyon . [9]

Primates

In humans, their average width is 50 micrometers.[ citation needed ]

Related Research Articles

<span class="mw-page-title-main">Lagomorpha</span> Order of mammals

The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae and the Ochotonidae (pikas). There are 110 recent species of lagomorph of which 109 are extant, including 10 genera of rabbits, 1 genus of hare and 1 genus of pika . The name of the order is derived from the Ancient Greek lagos + morphē.

<span class="mw-page-title-main">Multituberculata</span> Extinct order of mammals

Multituberculata is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, and reached a peak diversity during the Late Cretaceous and Paleocene. They eventually declined from the mid-Paleocene onwards, disappearing from the known fossil record in the late Eocene. They are the most diverse order of Mesozoic mammals with more than 200 species known, ranging from mouse-sized to beaver-sized. These species occupied a diversity of ecological niches, ranging from burrow-dwelling to squirrel-like arborealism to jerboa-like hoppers. Multituberculates are usually placed as crown mammals outside either of the two main groups of living mammals—Theria, including placentals and marsupials, and Monotremata—but usually as closer to Theria than to monotremes. They are considered to be closely related to Euharamiyida and Gondwanatheria as part of Allotheria.

Ferugliotherium is a genus of fossil mammals in the family Ferugliotheriidae from the Campanian and/or Maastrichtian period of Argentina. It contains a single species, Ferugliotherium windhauseni, which was first described in 1986. Although originally interpreted on the basis of a single brachydont (low-crowned) molar as a member of Multituberculata, an extinct group of small, rodent-like mammals, it was recognized as related to the hypsodont (high-crowned) Sudamericidae following the discovery of additional material in the early 1990s. After a jaw of the sudamericid Sudamerica was described in 1999, these animals were no longer considered to be multituberculates and a few fossils that were previously considered to be Ferugliotherium were assigned to unspecified multituberculates instead. Since 2005, a relationship between gondwanatheres and multituberculates has again received support. A closely related animal, Trapalcotherium, was described in 2009 on the basis of a single tooth.

Lavanify is a mammalian genus from the late Cretaceous of Madagascar. The only species, L. miolaka, is known from two isolated teeth, one of which is damaged. The teeth were collected in 1995–1996 and described in 1997. The animal is classified as a member of Gondwanatheria, an enigmatic extinct group with unclear phylogenetic relationships, and within Gondwanatheria as a member of the family Sudamericidae. Lavanify is most closely related to the Indian Bharattherium; the South American Sudamerica and Gondwanatherium are more distantly related. Gondwanatheres probably ate hard plant material.

<span class="mw-page-title-main">Asiatic linsang</span> Genus of carnivores

The Asiatic linsang (Prionodon) is a genus comprising two species native to Southeast Asia: the banded linsang and the spotted linsang. Prionodon is considered a sister taxon of the Felidae.

<span class="mw-page-title-main">Creodonta</span> Former order of extinct flesh-eating placental mammals

Creodonta is a former order of extinct carnivorous placental mammals that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia and Africa. Originally thought to be a single group of animals ancestral to the modern Carnivora, this order is now usually considered a polyphyletic assemblage of two different groups, the Oxyaenids and the Hyenodonts, not a natural group. Oxyaenids are first known from the Palaeocene of North America, while hyaenodonts hail from the Palaeocene of Africa.

<span class="mw-page-title-main">Simplicidentata</span> Group of mammals

Simplicidentata is a group of mammals that includes the rodents and their closest extinct relatives. The term has historically been used as an alternative to Rodentia, contrasting the rodents with their close relatives the lagomorphs. However, Simplicidentata is now defined as including all members of Glires that share a more recent common ancestor with living rodents than with living lagomorphs. Thus, Simplicidentata is a total group that is more inclusive than Rodentia, a crown group that includes all living rodents, their last common ancestor, and all its descendants. Under this definition, the loss of the second pair of upper incisors is a synapomorphic feature of Simplicidentata. The loss of the second upper premolar (P2) has also been considered as synapomorphic for Simplicidentata, but the primitive simplicidentate Sinomylus does have a P2.

<i>Purgatorius</i> Extinct genus of mammals

Purgatorius is a genus of seven extinct eutherian species typically believed to be the earliest example of a primate or a proto-primate, a primatomorph precursor to the Plesiadapiformes, dating to as old as 66 million years ago. The first remains were reported in 1965, from what is now eastern Montana's Tullock Formation, specifically at Purgatory Hill in deposits believed to be about 63 million years old, and at Harbicht Hill in the lower Paleocene section of the Hell Creek Formation. Both locations are in McCone County, Montana.

<span class="mw-page-title-main">Bristle-spined rat</span> Species of rodent

The bristle-spined rat is an arboreal rodent from the Atlantic forest in eastern Brazil. Also known as the bristle-spined porcupine or thin-spined porcupine, it is the only member of the genus Chaetomys and the subfamily Chaetomyinae. It was officially described in 1818, but rarely sighted since, until December 1986, when two specimens - one a pregnant female - were found in the vicinity of Valencia in Bahia. Since then it has been recorded at several localities in eastern Brazil, from Sergipe to Espírito Santo, but it remains rare and threatened due to habitat loss, poaching and roadkills.

<i>Diatomys</i> Extinct genus of rodents

Diatomys is an extinct rodent genus known from Miocene deposits in China, Japan, Pakistan, and Thailand. The fossil range is from the late Early Miocene to the Middle Miocene.

<i>Pyrotherium</i> Extinct genus of mammals

Pyrotherium is an extinct genus of South American ungulate, of the order Pyrotheria, that lived in what is now Argentina and Bolivia, during the Late Oligocene. It was named Pyrotherium because the first specimens were excavated from an ancient volcanic ash deposit. Fossils of the genus have been found in the Deseado and Sarmiento Formations of Argentina and the Salla Formation of Bolivia.

<span class="mw-page-title-main">Miacoidea</span> Extinct superfamily of carnivores

Miacoidea is a former paraphyletic superfamily of extinct placental mammals that lived during the Paleocene and Eocene epochs, about 66-33,9 million years ago. This group had been traditionally divided into two families of primitive carnivorous mammals: Miacidae and Viverravidae. These mammals were basal to order Carnivora, the crown-group within the Carnivoramorpha.

<i>Noronhomys</i> Extinct rat species from the islands of Fernando de Noronha off northeastern Brazil

Noronhomys vespuccii, also known as Vespucci's rodent, is an extinct rat species from the islands of Fernando de Noronha off northeastern Brazil. Italian explorer Amerigo Vespucci may have seen it on a visit to Fernando de Noronha in 1503, but it subsequently became extinct, perhaps because of the exotic rats and mice introduced by the first explorers of the island. Numerous but fragmentary fossil remains of the animal, of uncertain but probably Holocene age, were discovered in 1973 and described in 1999.

<span class="mw-page-title-main">Tillodontia</span> Extinct suborder of mammals

Tillodontia is an extinct suborder of eutherian mammals known from the Early Paleocene to Late Eocene of China, the Late Paleocene to Middle Eocene of North America where they display their maximum species diversity, the Middle Eocene of Pakistan, and the Early Eocene of Europe. Leaving no descendants, they are most closely related to the pantodonts, another extinct group. The tillodonts were medium- to large-sized animals that probably feed on roots and tubers in temperate to subtropical habitats.

<i>Pachygenelus</i> Extinct genus of cynodonts

Pachygenelus is an extinct genus of tritheledontid cynodonts. Fossils have been found from the Karoo basin in South Africa and date back to the Early Jurassic.

<span class="mw-page-title-main">Tooth</span> Hard, calcified structure found in the mouths of many vertebrates

A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tearing food, for defensive purposes, to intimidate other animals often including their own, or to carry prey or their young. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the outermost embryonic germ layer, the ectoderm.

LACM 149371 is an enigmatic fossil mammalian tooth from the Paleogene of Peru. It is from the Santa Rosa fossil site, which is of uncertain age but possibly late Eocene or Oligocene. The tooth is poorly preserved and may have been degraded by acidic water or because it passed through a predator's digestive tract. Its largest dimension is 2.65 mm. It is triangular in shape and bears six cusps that surround the middle of the tooth, where there are three basins (fossae). Crests connects the cusps and separate the fossae. The microscopic structure of the enamel is poorly preserved.

<span class="mw-page-title-main">Mammal tooth</span> Details of teeth found in many warm-blooded vertebrate animals

Teeth are common to most vertebrates, but mammalian teeth are distinctive in having a variety of shapes and functions. This feature first arose among early therapsids during the Permian, and has continued to the present day. All therapsid groups with the exception of the mammals are now extinct, but each of these groups possessed different tooth patterns, which aids with the classification of fossils.

Bharattherium is a mammal that lived in India during the Maastrichtian and possibly the Paleocene. The genus has a single species, Bharattherium bonapartei. It is part of the gondwanathere family Sudamericidae, which is also found in Madagascar and South America during the latest Cretaceous. The first fossil of Bharattherium was discovered in 1989 and published in 1997, but the animal was not named until 2007, when two teams independently named the animal Bharattherium bonapartei and Dakshina jederi. The latter name is now a synonym. Bharattherium is known from a total of eight isolated fossil teeth, including one incisor and seven molariforms.

Rodcania is an extinct genus of mammal, belonging to the order Xenungulata. It contains a single species, Rodcania kakan, which lived during the Paleocene. Its remains were found in South America. The genus name is an anagram of Carodnia.

References

  1. 1 2 Line and Bergqvist, 2005, p. 924
  2. 1 2 Martin, 1994, p. 121
  3. Martin, 2004, p. 411
  4. Martin, 2004, p. 417
  5. Martin, 2004, p. 418
  6. Martin, 2004, p. 419
  7. Martin, 1994, pp. 121–122
  8. Barycka, 2007, p. 276
  9. Stefen, Clara (2001). "Enamel Structure of Arctoid Carnivora: Amphicyonidae, Ursidae, Procyonidae, and Mustelidae". Journal of Mammalogy. 82 (2): 450–462. doi: 10.1644/1545-1542(2001)082<0450:ESOACA>2.0.CO;2 . ISSN   0022-2372. JSTOR   1383726. S2CID   85871953.

Literature cited