what order of mammals do humans belong to

Identify characteristics of mammals

Mammals are vertebrates that possess hair and mammary glands. Several other characteristics are distinctive to mammals, including sure features of the jaw, skeleton, integument, and internal anatomy. Modernistic mammals vest to three clades: monotremes, marsupials, and eutherians (or placental mammals).

Learning Objectives

• Identify characteristics of mammals
• Name and describe the distinguishing features of the three main groups of mammals
• Describe the evolutionary history of mammals
• Identify characteristics of primates
• Describe the evolutionary history of primates
• Describe the evolutionary history of humans

Mammals

Characteristics of Mammals

The presence of pilus is 1 of the nigh obvious signs of a mammal. Although it is not very extensive on certain species, such as whales, hair has many of import functions for mammals. Mammals are endothermic, and pilus provides insulation to retain oestrus generated past metabolic work. Hair traps a layer of air close to the trunk, retaining heat. Forth with insulation, hair can serve as a sensory machinery via specialized hairs chosen vibrissae, better known as whiskers. These attach to nerves that transmit information about sensation, which is particularly useful to nocturnal or burrowing mammals. Hair can too provide protective coloration or be function of social signaling, such as when an beast's pilus stands "on terminate."

Mammalian integument, or skin, includes secretory glands with various functions. Sebaceous glands produce a lipid mixture chosen sebum that is secreted onto the hair and skin for h2o resistance and lubrication. Sebaceous glands are located over nearly of the body. Eccrine glands produce sweat, or perspiration, which is mainly equanimous of h2o. In virtually mammals, eccrine glands are limited to certain areas of the trunk, and some mammals exercise not possess them at all. All the same, in primates, especially humans, sweat figures prominently in thermoregulation, regulating the body through evaporative cooling. Sweat glands are located over near of the trunk surface in primates. Apocrine glands, or smell glands, secrete substances that are used for chemical communication, such as in skunks. Mammary glands produce milk that is used to feed newborns. While male person monotremes and eutherians possess mammary glands, male person marsupials do not. Mammary glands probable are modified sebaceous or eccrine glands, but their evolutionary origin is not entirely clear.

Figure 1. Bones of the mammalian inner ear are modified from basic of the jaw and skull. (credit: NCI)

The skeletal system of mammals possesses many unique features. The lower jaw of mammals consists of only one bone, the dentary. The jaws of other vertebrates are equanimous of more than one os. In mammals, the dentary bone joins the skull at the squamosal bone, while in other vertebrates, the quadrate bone of the jaw joins with the articular bone of the skull. These bones are present in mammals, but they have been modified to function in hearing and grade bones in the middle ear (Effigy 1). Other vertebrates possess only 1 middle ear os, the stapes. Mammals have three: the malleus, incus, and stapes. The malleus originated from the articular bone, whereas the incus originated from the quadrate bone. This organization of jaw and ear bones aids in distinguishing fossil mammals from fossils of other synapsids.

The adductor muscle that closes the jaw is composed of two muscles in mammals: the temporalis and the masseter. These allow side-to-side movement of the jaw, making chewing possible, which is unique to mammals. Near mammals have heterodont teeth, meaning that they have different types and shapes of teeth rather than only one type and shape of molar. Most mammals are diphyodonts, meaning that they accept two sets of teeth in their lifetime: deciduous or "baby" teeth, and permanent teeth. Other vertebrates are polyphyodonts, that is, their teeth are replaced throughout their entire life.

Mammals, like birds, possess a four-chambered heart. Mammals too take a specialized group of cardiac fibers located in the walls of their right atrium called the sinoatrial node, or pacemaker, which determines the rate at which the heart beats. Mammalian erythrocytes (red blood cells) do not have nuclei, whereas the erythrocytes of other vertebrates are nucleated.

The kidneys of mammals have a portion of the nephron called the loop of Henle or nephritic loop, which allows mammals to produce urine with a high concentration of solutes, higher than that of the blood. Mammals lack a renal portal organization, which is a system of veins that moves blood from the hind or lower limbs and region of the tail to the kidneys. Renal portal systems are present in all other vertebrates except jawless fishes. A urinary float is present in all mammals.

Mammalian brains have sure characteristics that differ from other vertebrates. In some, but not all mammals, the cerebral cortex, the outermost part of the cerebrum, is highly folded, allowing for a greater surface area than is possible with a smooth cortex. The optic lobes, located in the midbrain, are divided into two parts in mammals, whereas other vertebrates possess a single, undivided lobe. Eutherian mammals also possess a specialized structure that links the two cerebral hemispheres, chosen the corpus callosum.

Groups of Mammals

There are three groups of mammals: the eutherians, or placental mammals, the marsupials, and the monotremes, or metatherians. These groups are divided into two clades: the eutherians and marsupials comprise the clade of therian mammals, and monotremes form their sister clade.

Marsupials

Figure 2. The Tasmanian devil is one of several marsupials native to Australia. (credit: Wayne McLean)

Marsupials are institute primarily in Australia, though the opossum is constitute in North America. Australian marsupials include the kangaroo, koala, bandicoot, Tasmanian devil (Figure 2), and several other species. Most species of marsupials possess a pouch in which the very premature young reside afterwards birth, receiving milk and continuing to develop. Marsupials differ from eutherians in that there is a less complex placental connexion: The young are born at an extremely early age and latch onto the nipple within the pouch.

Eutherians

Eutherians are the about widespread of the mammals, occurring throughout the world. At that place are 18 to twenty orders of placental mammals. Some examples are Insectivora, the insect eaters; Edentata, the toothless anteaters; Rodentia, the rodents; Cetacea, the aquatic mammals including whales; Carnivora, cannibal mammals including dogs, cats, and bears; and Primates, which includes humans. Eutherian mammals are sometimes chosen placental mammals because all species possess a complex placenta that connects a fetus to the mother, allowing for gas, fluid, and nutrient substitution. While other mammals possess a less circuitous placenta or briefly accept a placenta, all eutherians possess a complex placenta during gestation.

Monotremes

There are three living species of monotremes: the platypus and two species of echidnas, or spiny anteaters. The leathery-beaked platypus belongs to the family Ornithorhynchidae ("bird beak"), whereas echidnas belong to the family Tachyglossidae ("sticky tongue") (Figure 3). The platypus and one species of echidna are found in Australia, and the other species of echidna is constitute in New Republic of guinea. Monotremes are unique among mammals as they lay eggs, rather than giving birth to live young. The shells of their eggs are not like the difficult shells of birds, but are a leathery trounce, similar to the shells of reptile eggs. Monotremes have no teeth.

Figure 3. (a) The platypus, a monotreme, possesses a leathery beak and lays eggs rather than giving nativity to live immature. (b) The echidna is another monotreme. (credit b: modification of work by Barry Thomas)

Evolution of Mammals

Figure four. Cynodonts, which first appeared in the Late Permian menses 260 million years ago, are thought to be the ancestors of modern mammals. (credit: Nobu Tamura)

Mammals are synapsids, significant they have a single opening in the skull. They are the just living synapsids, as before forms became extinct by the Jurassic menses. The early not-mammalian synapsids can be divided into two groups, the pelycosaurs and the therapsids. Within the therapsids, a group called the cynodonts are thought to be the ancestors of mammals (Figure 4).

A key feature of synapsids is endothermy, rather than the ectothermy seen in most other vertebrates. The increased metabolic rate required to internally modify body temperature went hand in mitt with changes to certain skeletal structures. The later on synapsids, which had more evolved characteristics unique to mammals, possess cheeks for holding food and heterodont teeth, which are specialized for chewing, mechanically breaking down food to speed digestion and releasing the free energy needed to produce heat. Chewing also requires the ability to chew and breathe at the same fourth dimension, which is facilitated by the presence of a secondary palate. A secondary palate separates the area of the oral cavity where chewing occurs from the area above where respiration occurs, allowing animate to proceed uninterrupted during chewing. A secondary palate is not found in pelycosaurs but is present in cynodonts and mammals. The jawbone also shows changes from early on synapsids to later ones. The zygomatic arch, or cheekbone, is present in mammals and avant-garde therapsids such as cynodonts, but is not present in pelycosaurs. The presence of the zygomatic arch suggests the presence of the masseter muscle, which closes the jaw and functions in chewing.

In the appendicular skeleton, the shoulder girdle of therian mammals is modified from that of other vertebrates in that information technology does non possess a procoracoid bone or an interclavicle, and the scapula is the ascendant bone.

Mammals evolved from therapsids in the late Triassic catamenia, equally the earliest known mammal fossils are from the early on Jurassic period, some 205 one thousand thousand years ago. Early mammals were small, about the size of a minor rodent. Mammals kickoff began to diversify in the Mesozoic Era, from the Jurassic to the Cretaceous periods, although nearly of these mammals were extinct by the end of the Mesozoic. During the Cretaceous period, some other radiation of mammals began and connected through the Cenozoic Era, about 65 1000000 years agone.

In Summary: Mammals

Mammals in full general are vertebrates that possess hair and mammary glands. The mammalian integument includes various secretory glands, including sebaceous glands, eccrine glands, apocrine glands, and mammary glands. Mammals are synapsids, pregnant that they have a single opening in the skull. A key characteristic of synapsids is endothermy rather than the ectothermy seen in other vertebrates. Mammals probably evolved from therapsids in the belatedly Triassic period, equally the earliest known mammal fossils are from the early Jurassic period. In that location are three groups of mammals living today: monotremes, marsupials, and eutherians. Monotremes are unique among mammals every bit they lay eggs, rather than giving birth to young. Eutherian mammals are sometimes called placental mammals, considering all species possess a circuitous placenta that connects a fetus to the mother, assuasive for gas, fluid, and nutrient commutation.

Primates

Characteristics of Primates

Order Primates of class Mammalia includes lemurs, tarsiers, monkeys, apes, and humans. Non-homo primates live primarily in the tropical or subtropical regions of Southward America, Africa, and Asia. They range in size from the mouse lemur at 30 grams (1 ounce) to the mountain gorilla at 200 kilograms (441 pounds). The characteristics and development of primates is of particular interest to us every bit information technology allows united states of america to understand the evolution of our own species.

All primate species possess adaptations for climbing trees, as they all descended from tree-dwellers. This arboreal heritage of primates has resulted in hands and feet that are adjusted for brachiation, or climbing and swinging through trees. These adaptations include, but are not express to: 1) a rotating shoulder joint, ii) a big toe that is widely separated from the other toes and thumbs, which are widely separated from fingers (except humans), which let for gripping branches, 3) stereoscopic vision, two overlapping fields of vision from the optics, which allows for the perception of depth and gauging altitude. Other characteristics of primates are brains that are larger than those of nigh other mammals, claws that have been modified into flattened nails, typically only one offspring per pregnancy, and a trend toward belongings the trunk upright.

Social club Primates is divided into ii groups: prosimians and anthropoids. Prosimians include the bush babies of Africa, the lemurs of Madagascar, and the lorises, pottos, and tarsiers of Southeast Asia. Anthropoids include monkeys, apes, and humans. In full general, prosimians tend to be nocturnal (in contrast to diurnal anthropoids) and exhibit a smaller size and smaller brain than anthropoids.

Evolution of Primates

The commencement primate-like mammals are referred to as proto-primates. They were roughly similar to squirrels and tree shrews in size and appearance. The existing fossil prove (mostly from Due north Africa) is very fragmented. These proto-primates remain largely mysterious creatures until more than fossil show becomes available. The oldest known primate-similar mammals with a relatively robust fossil record is Plesiadapis (although some researchers do not agree that Plesiadapis was a proto-primate). Fossils of this primate have been dated to approximately 55 1000000 years ago. Plesiadapiforms were proto-primates that had some features of the teeth and skeleton in common with truthful primates. They were found in North America and Europe in the Cenozoic and went extinct by the end of the Eocene.

The showtime truthful primates were found in Due north America, Europe, Asia, and Africa in the Eocene Epoch. These early primates resembled present-day prosimians such as lemurs. Evolutionary changes continued in these early primates, with larger brains and eyes, and smaller muzzles existence the trend. By the stop of the Eocene Epoch, many of the early on prosimian species went extinct due either to libation temperatures or competition from the kickoff monkeys.

Effigy v. The howler monkey is native to Central and S America. It makes a call that sounds like a lion roaring. (credit: Xavi Talleda)

Anthropoid monkeys evolved from prosimians during the Oligocene Epoch. Past 40 meg years ago, bear witness indicates that monkeys were nowadays in the New World (South America) and the Old World (Africa and Asia). New World monkeys are as well chosen Platyrrhini—a reference to their broad noses (Figure 5). Old World monkeys are chosen Catarrhini—a reference to their narrow noses. There is still quite a bit of uncertainty nearly the origins of the New World monkeys. At the time the platyrrhines arose, the continents of South American and Africa had drifted apart. Therefore, it is thought that monkeys arose in the Old World and reached the New World either by drifting on log rafts or by crossing state bridges. Due to this reproductive isolation, New Earth monkeys and Old World monkeys underwent carve up adaptive radiation over millions of years. The New World monkeys are all arboreal, whereas Old World monkeys include arboreal and basis-dwelling species.

Apes evolved from the catarrhines in Africa midway through the Cenozoic, approximately 25 million years ago. Apes are more often than not larger than monkeys and they practise not possess a tail. All apes are capable of moving through trees, although many species spend virtually their time on the footing. Apes are more intelligent than monkeys, and they have relatively larger brains proportionate to torso size. The apes are divided into two groups. The lesser apes comprise the family Hylobatidae, including gibbons and siamangs. The nifty apes include the genera Pan (chimpanzees and bonobos) (Figure 6a), Gorilla (gorillas), Pongo (orangutans), and Human (humans) (Effigy 6b). The very arboreal gibbons are smaller than the smashing apes; they take low sexual dimorphism (that is, the sexes are not markedly dissimilar in size); and they have relatively longer arms used for swinging through copse.

Figure 6. The (a) chimpanzee is i of the cracking apes. Information technology possesses a relatively large brain and has no tail. (b) All groovy apes have a similar skeletal structure. (credit a: modification of work past Aaron Logan; credit b: modification of work by Tim Vickers)

Evolution of Humans

The family Hominidae of social club Primates includes the hominoids: the great apes (Effigy seven). Evidence from the fossil record and from a comparing of human being and chimpanzee Deoxyribonucleic acid suggests that humans and chimpanzees diverged from a common hominoid ancestor approximately vi million years ago. Several species evolved from the evolutionary branch that includes humans, although our species is the just surviving member. The term hominin is used to refer to those species that evolved afterwards this split of the primate line, thereby designating species that are more closely related to humans than to chimpanzees. Hominins were predominantly bipedal and include those groups that probable gave rise to our species—including Australopithecus, Man habilis, and Human being erectus—and those non-bequeathed groups that can be considered "cousins" of modernistic humans, such as Neanderthals. Determining the truthful lines of descent in hominins is difficult. In years past, when relatively few hominin fossils had been recovered, some scientists believed that because them in lodge, from oldest to youngest, would demonstrate the grade of development from early hominins to modern humans. In the past several years, however, many new fossils have been found, and information technology is clear that there was often more than than one species alive at any one time and that many of the fossils establish (and species named) represent hominin species that died out and are non ancestral to modernistic humans.

Effigy 7. This chart shows the evolution of modern humans.

Very Early Hominins

Iii species of very early hominids have made news in the past few years. The oldest of these, Sahelanthropus tchadensis, has been dated to nearly 7 one thousand thousand years ago. In that location is a single specimen of this genus, a skull that was a surface find in Republic of chad. The fossil, informally called "Toumai," is a mosaic of primitive and evolved characteristics, and it is unclear how this fossil fits with the picture given by molecular information, namely that the line leading to mod humans and modern chimpanzees apparently bifurcated about 6 million years ago. It is not thought at this fourth dimension that this species was an ancestor of modern humans.

A 2d, younger species, Orrorin tugenensis, is also a relatively recent discovery, found in 2000. There are several specimens ofOrrorin. Information technology is not known whether Orrorin was a homo ancestor, but this possibility has not been ruled out. Some features of Orrorinare more like to those of modern humans than are the australopiths, although Orrorin is much older.

A third genus, Ardipithecus, was discovered in the 1990s, and the scientists who discovered the beginning fossil plant that some other scientists did not believe the organism to be a biped (thus, it would non be considered a hominid). In the intervening years, several more specimens of Ardipithecus, classified equally 2 different species, demonstrated that the organism was bipedal. Once again, the status of this genus as a human ancestor is uncertain.

Early Hominins: Genus Australopithecus

Australopithecus ("southern ape") is a genus of hominin that evolved in eastern Africa approximately 4 million years ago and went extinct about two million years ago. This genus is of item interest to usa as it is thought that our genus, genus Human being, evolved fromAustralopithecus about two million years ago (after likely passing through some transitional states). Australopithecus had a number of characteristics that were more than similar to the great apes than to modern humans. For example, sexual dimorphism was more than exaggerated than in modern humans. Males were up to 50 percent larger than females, a ratio that is similar to that seen in modern gorillas and orangutans. In dissimilarity, modern human males are approximately xv to xx percent larger than females. The brain size ofAustralopithecus relative to its body mass was as well smaller than modern humans and more similar to that seen in the bully apes. A central feature that Australopithecus had in common with mod humans was bipedalism, although it is likely that Australopithecus also spent fourth dimension in trees. Hominin footprints, like to those of modern humans, were found in Laetoli, Tanzania and dated to 3.6 million years ago. They showed that hominins at the fourth dimension of Australopithecus were walking upright.

In that location were a number of Australopithecus species, which are oftentimes referred to as australopiths. Australopithecus anamensis lived about four.ii meg years ago. More is known virtually another early species, Australopithecus afarensis, which lived betwixt 3.9 and 2.9 million years ago. This species demonstrates a trend in human evolution: the reduction of the dentition and jaw in size. A. afarensis (Effigy 8) had smaller canines and molars compared to apes, simply these were larger than those of modern humans.

Effigy 8. The skull of (a) Australopithecus afarensis, an early hominid that lived between ii and iii million years ago, resembled that of (b) mod humans but was smaller with a sloped forehead and prominent jaw.

Its brain size was 380–450 cubic centimeters, approximately the size of a modern chimpanzee brain. Information technology likewise had prognathic jaws, which is a relatively longer jaw than that of modern humans. In the mid-1970s, the fossil of an adult female A. afarensis was found in the Afar region of Ethiopia and dated to 3.24 million years ago (Figure 9). The fossil, which is informally called "Lucy," is significant because it was the about complete australopith fossil institute, with 40 percent of the skeleton recovered.

Figure 9. This adult female Australopithecus afarensis skeleton, nicknamed Lucy, was discovered in the mid 1970s. (credit: "120"/Wikimedia Commons)

Australopithecus africanus lived between 2 and 3 meg years ago. It had a slender build and was bipedal, but had robust arm bones and, like other early hominids, may have spent significant time in trees. Its brain was larger than that of A. afarensis at 500 cubic centimeters, which is slightly less than 1-third the size of modernistic human brains. Two other species, Australopithecus bahrelghazaliand Australopithecus garhi, have been added to the roster of australopiths in contempo years.

A Dead End: Genus Paranthropus

The australopiths had a relatively slender build and teeth that were suited for soft food. In the past several years, fossils of hominids of a different trunk type have been found and dated to approximately 2.five million years agone. These hominids, of the genus Paranthropus, were relatively large and had large grinding teeth. Their molars showed heavy habiliment, suggesting that they had a coarse and fibrous vegetarian nutrition as opposed to the partially carnivorous diet of the australopiths. Paranthropus includes Paranthropus robustus of S Africa, and Paranthropus aethiopicus and Paranthropus boisei of East Africa. The hominids in this genus went extinct more than 1 one thousand thousand years agone and are not thought to exist bequeathed to modern humans, merely rather members of an evolutionary co-operative on the hominin tree that left no descendants.

Early Hominins: Genus Human being

The homo genus, Human, kickoff appeared between two.5 and 3 1000000 years ago. For many years, fossils of a species called H. habiliswere the oldest examples in the genus Homo, but in 2010, a new species called Homo gautengensis was discovered and may be older. Compared to A. africanus, H. habilis had a number of features more similar to modern humans. H. habilis had a jaw that was less prognathic than the australopiths and a larger brain, at 600–750 cubic centimeters. Nevertheless, H. habilis retained some features of older hominin species, such as long arms. The proper noun H. habilis means "handy man," which is a reference to the stone tools that accept been institute with its remains.

Lookout this video nearly Smithsonian paleontologist Briana Pobiner explaining the link between hominin eating of meat and evolutionary trends.

Figure 10.Homo erectus had a prominent brow and a olfactory organ that pointed downward rather than frontward.

H. erectus appeared approximately 1.viii million years ago (Figure ten). It is believed to have originated in Eastward Africa and was the first hominin species to migrate out of Africa. Fossils of H. erectus have been found in India, China, Java, and Europe, and were known in the past as "Java Man" or "Peking Human." H. erectus had a number of features that were more similar to modern humans than those ofH. habilis. H. erectus was larger in size than before hominins, reaching heights upwards to 1.85 meters and weighing up to 65 kilograms, which are sizes similar to those of modernistic humans. Its degree of sexual dimorphism was less than before species, with males being 20 to xxx per centum larger than females, which is close to the size departure seen in our species. H. erectus had a larger brain than earlier species at 775–i,100 cubic centimeters, which compares to the 1,130–1,260 cubic centimeters seen in modern human brains. H.erectus likewise had a olfactory organ with downward-facing nostrils similar to modern humans, rather than the forrad facing nostrils found in other primates. Longer, down-facing nostrils allow for the warming of cold air earlier it enters the lungs and may accept been an adaptation to colder climates. Artifacts found with fossils of H. erectus suggest that information technology was the showtime hominin to utilise fire, hunt, and take a home base. H. erectus is more often than not idea to have lived until most 50,000 years ago.

Humans: Homo sapiens

Effigy eleven. The Homo neanderthalensis used tools and may accept worn clothing.

A number of species, sometimes called archaic Human sapiens, apparently evolved from H. erectus starting about 500,000 years ago. These species include Homo heidelbergensis, Homo rhodesiensis, and Human neanderthalensis. These primitive H. sapiens had a brain size similar to that of modern humans, averaging one,200–1,400 cubic centimeters. They differed from modern humans by having a thick skull, a prominent brow ridge, and a receding mentum. Some of these species survived until 30,000–10,000 years ago, overlapping with modern humans (Effigy 11).

There is considerable contend virtually the origins of anatomically modern humans or Human sapiens sapiens . Every bit discussed earlier, H.erectus migrated out of Africa and into Asia and Europe in the first major wave of migration virtually 1.5 million years agone. It is idea that mod humans arose in Africa from H. erectus and migrated out of Africa about 100,000 years ago in a second major migration wave. Then, modern humans replaced H. erectus species that had migrated into Asia and Europe in the beginning wave.

This evolutionary timeline is supported past molecular evidence. One approach to studying the origins of modernistic humans is to examine mitochondrial Dna (mtDNA) from populations around the world. Because a fetus develops from an egg containing its mother's mitochondria (which have their ain, not-nuclear Deoxyribonucleic acid), mtDNA is passed entirely through the maternal line. Mutations in mtDNA tin now be used to gauge the timeline of genetic divergence. The resulting testify suggests that all modern humans accept mtDNA inherited from a common ancestor that lived in Africa about 160,000 years ago. Another approach to the molecular agreement of human evolution is to examine the Y chromosome, which is passed from father to son. This evidence suggests that all men today inherited a Y chromosome from a male person that lived in Africa nigh 140,000 years ago.

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