Heterodont animals *

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1 OpenStax-CNX module: m Heterodont animals * Marcos Gridi-Papp This work is produced by OpenStax-CNX and licensed under the Creative Commons Attribution License 4.0 Abstract Mammals evolved a heterodont dentition with four classes of teeth: incisors, canines, premolars and molars. Each tooth is formed by 1-5 cusps. Maxillary cusps are called cones whereas mandibular ones are called conids. Hypsodont teeth erupt high beyond the gum line while brachydont teeth do not protrude much. The shape and arrangement of tissues in the molar teeth is grouped into several classes that reect the diet and phylogeny of the animals. * Version 1.1: Feb 14, :54 am

OpenStax-CNX module: m66060 2 1 Mammalian teeth Figure 1: The tiger (Panthera tigris) presents an example of heterodont dentition with four types of teeth. More details 1.

2 OpenStax-CNX module: m Mammalian teeth Figure 1: The tiger (Panthera tigris) presents an example of heterodont dentition with four types of teeth. More details 1. Mammals have evolved heterodont dentitions. They are unique in having four tooth classes: incisors, canines, premolars and molars. These classes are found in the majority of species, and always in the same order (but in variable numbers) from the midline to the sides. Each type is formed by 1-5 cusps, which are round projections of the crown pointing toward the opposing tooth. Incisors are the most medial and anterior teeth. They vary in number from none in armadillos, to 18 in opossums. They are broad and at, and their single cusp forms a broad cutting line called the incisal edge. The general function of incisors is seizing food and biting o pieces of food items. Mammals that gnaw, like rabbits and mice, have relatively large incisors lacking on the posterior surface. As enamel wears more slowly than dentin, the tooth maintains a chisel shape with a sharp incisal edge. Elephants have highly specialized incisors that evolved into a round shape and extended out of the mouth to form tusks. Canines are round and pointy, frequently being the longest teeth of mammals. They present a single cusp and are also called cuspids. Mammals have 0-4 canines, which are used to puncture the food item during biting, producing a rm hold helping to kill prey. Hervibores commonly lack canines, or have them modied into tusks, like walruses and pigs, to serve as weapons or have other uses. 1

3 OpenStax-CNX module: m Early mammals had premolars with a single cusp and molars with three cusps, but they later evolved premolars with up to three cusps and molars with four or ve cusps. These teeth process the food in the mouth by cutting, slicing or grinding. 2 Cusps Upper molar cusps are called cones, whereas lower molar cusps are called conids. A prex is added to the name to specify their position on the tooth. These prexes are proto-, para-, meta-, hypo-, and ento-. A paracone is therefore the anterior external cusp of a maxillary molar. Tribosphenic molars with three cusps were found in early mammals and are still found in insectivores. Many modern mammals such as primates (humans), racoons and hedgehogs have quadrate molars however, containing four or ve cusps. Figure 2: Evolution of the arrangements of cusps in molar teeth of reptiles and early mammals. 1, Reptile; 2, Dromatherium; 3, Microconodon; 4, Spalacotherium; me, metaconid; pa, paraconid; pr, protoconid; 5, Amphitherium. (After Osborn.). More details 2. 3 Crown height Hypsodont 3 teeth are characterized by high crown with enamel that extends far past the gum line into the bone. These teeth are commonly found in grazing herbivores because they provide extra material for wear and tear. The tooth keeps erupting slowly as it is worn o. Some examples of animals with hypsodont teeth are cows 4 and horses. These animals usually die in nature of other causes before their molars wear o completely. But domesticated animals like old horses are frequently reported to loose to functionality of their molars because of extensive wearing. Rabbits and some rodents, on the other hand, incisors that continue growing after they erupt, adding new tissue at the roots as wearing progresses at the incisal edge. The opposite condition to hypsodont is brachydont. It is a type of dentition characterized by low-crowned teeth (brachys = short). Human teeth are brachydont. The tooth has a crown above the gingival line and a neck just below it, and at least one root. A cap of enamel covers the crown and extends down to the neck. Cementum is only found below the gingival line, covering the root

OpenStax-CNX module: m66060 4 4 Shape and arrangement of enamel and dentin 4.1 Bunodont The cusps are rounded instead of sharp or pointy.

4 OpenStax-CNX module: m Shape and arrangement of enamel and dentin 4.1 Bunodont The cusps are rounded instead of sharp or pointy. These molars are most common among omnivores such as pigs, bears and humans. Bunodont molars are eective crushing devices and often quadrate in shape. Figure 3: Pig molars are bunodont teeth. More details Lophodont These teeth are identied by the patterns of ridges or lophs of enamel interconnecting the cusps on the crowns. Present in most herbivores, these patterns of lophs can be a simple ring-like edge, as in mole rats 6, or a complex arrangement of series of ridges and cross-ridges, as those in odd-toed ungulates 7 (Perissodactyla), such as horses, tapirs and rhinoceroses

OpenStax-CNX module: m66060 5 Figure 4: Molars of the Asian elephant (Elephas 8 ; left), African elephant (Loxodonta 9 ; center) and Mastodon 10 (right).

5 OpenStax-CNX module: m Figure 4: Molars of the Asian elephant (Elephas 8 ; left), African elephant (Loxodonta 9 ; center) and Mastodon 10 (right). Elephants are mostly grazers with lophodont molars, whereas mastodons are believed to have been browsers of trees, shrubs and swamp vegetation and their molars were not lophodont. More details 11. Lophodont molars have hard and elongated enamel ridges called lophs oriented either along or perpendicular to the dental row. Lophodont molars are common in herbivores that grind their food thoroughly. Examples include tapirs 12, manatees 13, and many rodents. When two lophs form transverse, often ring-shaped, ridges on a tooth, the arrangement is called bilophodont. This pattern is common in primates, but can also be found in lagomorphs 14 (hare, rabbits, and pikas) and some rodents. Extreme forms of lophodonty in elephants 15 and some rodents (such as Otomys 16 ) is known as loxodonty. The African elephant 17 belongs to a genus called Loxodonta because of this feature. 4.3 Selenodont The major cusp in this type of molar is elongated into a crescent-shaped ridge. even-toed ungulates 18 (Artiodactyla), such as cows 19 and deer 20. This is found in most

OpenStax-CNX module: m66060 6 Figure 5: Selenodont teeth of a mountain goat. More details 21. 4.

6 OpenStax-CNX module: m Figure 5: Selenodont teeth of a mountain goat. More details Secodont Many carnivorous mammals have enlarged and blade-like teeth especially adapted for slicing and chopping called carnassials 22. A general term for such blade-like teeth is secodont or plagiaulacoid

OpenStax-CNX module: m66060 7 Figure 6: Carnassials of a Eurasian wolf. More details 23. 5 Figure credits Figure 1 by I, ArtMechanic, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?

7 OpenStax-CNX module: m Figure 6: Carnassials of a Eurasian wolf. More details Figure credits Figure 1 by I, ArtMechanic, CC BY-SA 3.0, Figure 2 by Frank E. Beddard - The Cambridge Natural History, Volume XMammalia., Public Domain, Figure 3 byblic Domain, Figure 4 by Originator: Hubert Ludwig - Schul-Naturgeschichte, Public Domain, Figure 5 by Grand Canyon NPS - Harrington's mountain goat grca uploaded by FunkMonk, CC BY 2.0, Figure 6 by Mariomassone (talk) 20:27, 12 August 2009 (UTC). - I Mariomassone (talk) 20:27, 12 August 2009 (UTC) created this work entirely by myself., Public Domain,

EUTHERIAN MAMMALS. Eutherian Mammals are classified into orders on the basis of dentition. It does not involve phylogeny.

EUTHERIAN MAMMALS. Eutherian Mammals are classified into orders on the basis of dentition. It does not involve phylogeny. EUTHERIAN MAMMALS Eutherian Mammals are classified into orders on the basis of dentition. It does not involve phylogeny. Dinosaurs..? TROPHIC TYPES FOUND AMONG EUTHERIAN MAMMALS Predators Flesh eaters