Erectus &/or Me

Skull low, broad and elongated Cranial capacity 900 cc Median sagittal ridge Supraorbital ridge Postorbital constriction Receding frontal contour Occipital bun or torus Nuchal area extended for muscle attachment Cranial wall unusually thick Brain case narrower than zygomatic arch Heavy facial architecture Alveolar (maxilla) prognathism Large jaw, wide ramus No chin (mentum) Teeth generally large Post-cranial bones heavy and thick

EUKARIOTES MITOCHONDRAL EUKARIOTES CROWN EUKARIOTES KINGDOM: METAZOA EUMETAZOA BILATERIA SUPERPHYLUM: DEUTEROSTOMIA PHYLUM: CHORDATA SOMITOFORMA CRANIATA SUBPHYLUM: VERTEBRATA GNATHOSTOMATA TELEOSTOMI OSTEICHTHYES SARCOPTERYGII CHOANATA TETRAPODA ANTHRACOSAURIA AMNIOTA SYNAPSIDA THERAPSIDA CLASS: MAMMALIA SUBCLASS: EUTHERIA (Placentals) ORDER: PRIMATES SUBORDER: HAPLORHINI INFRAORDER: CATARRHINI FAMILY: HOMINIDAE GENUS: HOMO SAPIENS SPECIES: SAPIENS SUBSPECIES: ERECTUS

The synapomorphic features of the eukaryotes is the nucleus with associated mitotic division system. The first eukaryotic cells probably also had a small array of cytoskeletal elements but these have yet to be identified.

Animal cells lack the rigid cell walls that characterize plant cells. The bodies of most animals (all except sponges) are made up of cells organized into tissues, each tissue specialized to some degree to perform specific functions. In most, tissues are organized into even more specialized organs. Most animals are capable of complex and relatively rapid movement compared to plants and other organisms. Most reproduce sexually, by means of differentiated eggs and sperm. Most animals are diploid, meaning that the cells of adults contain two copies of the genetic material. The development of most animals is characterized by distinctive stages, including a zygote, formed by the product of the first few division of cells following fertilization; a blastula, which is a hollow ball of cells formed by the developing zygote; and a gastrula, which is formed when the blastula folds in on itself to form a double-walled structure with an opening to the outside, the blastopore.

Somewhere around 9 or 10 million species of animals inhabit the earth; the exact number is not known and even our estimates are very rough. Animals range in size from no more than a few cells to organisms weighing many tons, such as blue whales and giant squid. Most animals inhabit the seas, with fewer in fresh water and even fewer on land.

The nerve cord of chordates develops dorsally in the body as a hollow tube above the notochord. In most species it differentiates in embryogeny into the brain anteriorly and spinal cord that runs through the trunk and tail. Together the brain and spinal cord are the central nervous system to which peripheral sensory and motor nerves connect.

The visceral (also called pharyngeal or gill) clefts and arches are located in the pharyngeal part of the digestive tract behind the oral cavity and anterior to the esophagus. The visceral clefts appear as several pairs of pouches that push outward from the lateral walls of the pharynx eventually to reach the surface to form the clefts. Thus the clefts are continuous, slit-like passages connecting the pharynx to the exterior. The soft and skeletal tissues between adjacent clefts are the visceral arches. The embryonic fate of the clefts and slits varies greatly depending on the taxonomic subgroup. In many of the non-vertebrate chordates, such as tunicates and cephalochordates, the clefts and arches are elaborated as straining devices concerned with capture of small food particles from water. In typical fish-like vertebrates and juvenile amphibians the walls of the pharyngeal clefts develop into gills that are organs of gas exchange between the water and blood. In adult amphibians and the amniote tetrapods (= reptiles, birds and mammals) the anterior most cleft transforms into the auditory (Eustachian) tube and middle ear chamber, whereas the other clefts disappear after making some important contributions to glands and lymphatic tissues in the throat region. The skeleton and muscles of the visceral arches are the source of a great diversity of adult structures in the vertebrates. For example, in humans (and other mammals) visceral arch derivatives include the jaw and facial muscles, the embryonic cartilaginous skeleton of the lower jaw, the alisphenoid bone in the side wall of the brain case, the three middle ear ossicles (malleus, incus and stapes), the skeleton and some musculature of the tongue, the skeleton and muscles of the larynx, and the cartilaginous tracheal rings.

The craniates are characterized by a skull; that is, a complex ensemble of skeletal elements which surrounds the brain and sensory capsules. The skull of hagfishes (top) consists of cartilaginous bars (blue), but the brain is mostly surrounded by a fibrous sheath underlain by the notochord. The skull of lampreys has a more elaborate braincase and comprises a large "branchial basket" surrounding the gills. In the gnathostomes, the braincase is generally closed.

The skull also encloses the brain, always comprising five parts referred to as the rhombencephalon, metencephalon, mesencephalon, diencephalon, and telencephalon. The metencephalon is developed into a cerebellum in the Gnathostomata and some fossil jawless vertebrates. The nerve fibres are primitively non-myelinated and become myelinated only in the gnathostomes. The brain is continued posteriorly by the spinal cord, which is ribbon-shaped but becomes thicker in the gnathostomes. As in cephalochordates, the dorsal (sensory) and ventral (motor) spinal nerves are initially separate, but unite in the gnathostomes. In all craniates, the olfactory (I), optic (II), trigeminal (V), facial (VII), acoustic (VIII), glossopharyngeal (IX) and vagus (X) cranial nerves are present. Additional cranial nerves, the oculomotor (III), trochlear (IV) and abducent (VI) nerves occur only in the Vertebrata. Some consider that the latter have been secondarily lost in hagfishes.

The olfactory organ opens into a median duct, the nasopharyngeal duct, which also serves the intake of the respiratory water. In most vertebrates, however, this duct becomes a blind tube and the intake of respiratory water is made through the mouth or the gill slits. The nasopharyngeal duct lies ventrally against the diencephalon and there, in ontogeny, induces the formation of an important gland, the hypophysis, or pituitary organ, which comprises neural (neurohypophysis) and glandular (adenohypophysis) parts. The adenohypophysis is particularly complex in the Vertebrata, but very simple in hagfishes.

Craniates possess a unique embryonic tissue, the neural crest, that appears dorsal and lateral to the neural tube and which contributes to a great variety of adult tissues and structures including: sensory neurons (nerve cells), some skeletal and connective tissues in the skull, and some pigment containing cells and other integumentary tissues. In the skull, the neural crest cells give rise to the gill arches, jaws and parts of the braincase floor. In the gnathostomes and a number of fossil jawless vertebrates, the neural crest cells are also involved in the formation of the dermal skeleton (scales, teeth, and dermal bones).

The gills of craniates comprise gill filaments, made up by primary and secondary gill lamellae which insure gas exchanges. In hagfishes, the gills have no skeletal support, and are enclosed in pouches connected to the pharynx. Among vertebrates, a similar structure occurs in adult lampreys only, but here skeletal supports (gill arches) are present. The gills are derived from tissues of the embryonic gut (endoderm), but cells from the embryonic skin (ectoderm) are involved in their formation in the gnathostomes. The respiratory water flow is ensured by a special pumping and anti-reflux organ, the velum, situated at the limit between the mouth and the pharynx. There is a theory that the jaws of the gnathostomes are derived from the velum.

As chordates, all craniates develop a notochord, which is primitively large (hagfishes, lampreys), but becomes transitory in most vertebrates and is replaced by elements of the vertebral column, the centra and arcualia.

All craniates (except most tetrapods) possess a caudal fin strengthened by a number of cartilaginous radials. In vertebrates appear dorsal and anal fins, as well as radial muscles which ensure undulatory movements of the fin web. In the gnathostomes and some fossil jawless vertebrates, there are paired pectoral fins. Only the gnathostomes possess both pectoral and pelvic fins, which are modified into locomotory limbs in tetrapods.

All craniates possess an endoskeleton, which is primitively cartilaginous but becomes mineralized in various ways (bone, calcified cartilage) in the vertebrates. Only the gnathostomes and a number of fossil jawless vertebrates possess a mineralized exoskeleton which develops in the skin tissues. The exoskeleton is made up by a variety of tissues (bone, dentine, enamel).

Craniates have a circulatory system of arteries, capillaries and veins, and a chambered, muscular main heart located ventrally and anteriorly in the trunk. In the Vertebrata, the circulatory system is entirely closed. The two heart chambers, the atrium and ventricle are well apart. There are additional accessory venous hearts in the head and tail, which help in venous blood circulation, but these are lost in the Vertebrata. In gill-breathing craniates, the heart pumps venous blood anteriorly into arteries and capillaries in the gills for gas (oxygen and carbon dioxide) exchange with water. Oxygenated blood then collects dorsal to the gills and flows anteriorly to the head and posteriorly to the organs and muscles, and back to the heart. In some Vertebrata (Osteichthyes) diverticles of the digestive tract (lungs or air bladder) supplements or replaces gills as the repiratory organ.

The digestive tract of craniates is longitudinally differentiated into mouth and oral cavity, pharynx, esophagus, intestine, rectum and anus. A stomach is developed in the Gnathostomata and some fossil jawless Vertebrates. All craniates have a pancreas that produces digestive enzymes and hormones (insulin and glucagon) that regulate blood sugar level. The pancreas was ancestrally disseminated along the anterior part of the gut, but becomes condensed into a well-defined organ in the Vertebrata.

All craniates and the related cephalochordates have a liver or hepatic organ that serves many functions including food storage and production of fat emulsifiers (bile).

The kidneys are the chief excretory organs of vertebrates and these organs play an important role in water and salt balance. Although kidneys vary greatly in size, shape and position among species, all contain nephrons as the basic functional units. Each nephron is a nearly microscopic tubule that receives a filtrate of blood (lacking blood cells and very large molecules). The filtrate is processed by selective secretion and reabsorption of materials to produce an excretory product (generally called urine) that contains nitrogenous waste and other materials. Long and complex kidney tubules occur only in the vertebrates.

• Metamerically arranged endoskeletal elements flanking the spinal cord. There are primitively two pairs of such elements in each metamere and on each side: the interdorsals and basidorsals. In the gnathostomes, there are two additional pairs ventrally to the notochord: the interventrals and basiventrals. These elements are called arcualia and can fuse to a notochordal calcification, the centrum. The ensemble of the arcualia + centrum is the vertebra, and the ensemble of the vertebrae is the vertebral column.
  The vertebrates are characterized by a vertebral column; that is, a variable number of endoskeletal elements aligned along the notochord and flanking the spinal cord. In lampreys, the vertebral elements are only the basidorsal and the interdorsals . In the gnathostomes, there are in addition ventral elements, the basiventrals and interventrals , and the notochord may calcify into centra.
• Extrinsic eye muscles. These muscles are attached to the eyeball and orbital wall, and ensure eye movements
• Radial muscles in fins. These are small muscles associated with each of the cartilaginous radials of the unpaired and paired fins. They ensure the undulatory movements of the fin web.
• Atrium and ventricle of heart closely-set.
• Nervous regulation of heart. The heart in the embryo of the vertebrates is aneural, like the heart of adult hagfishes. In adult vertebrates, however, the heart is innervated by a branch of the vagus nerve.
• Typhlosole in the intestine. This is a spirally coiled fold of the intestinal wall. In the Gnathostomes, it can be developed into a complex spiral valve.
• At least two vertical semicircular canals in the labyrinth
• True neuromasts in the sensory-line system

• A vertically biting device called jaws, and which is primitively made up by two endoskeletal elements, the palatoquadrate and Meckelian cartilage, and a number of dermal elements called teeth, sometimes attached to large dermal bones.
  The skull of a gnathostome, or jawed vertebrates, are characterized by vertically biting jaws consisting of the palatoquadrate dorsally and the Meckelian cartilage ventrally. The gill arches are situated internally to the gill filaments, and the nasal capsules open to the exterior by means of paired nostrils.
• Pelvic fins. These are the paired fins or limbs situated just in front of the anus.
• Interventrals and basiventrals in the backbone. These are the elements of the backbone which lie under the notochord, and match the basidorsals and interdorsals respectively.
• Gill arches which lie internally to the gills and branchial blood vessels, contrary to the gill arches of all jawless craniates, which are external to the gills and blood vessels.
• A horizontal semicircular canal in the inner ear
• Paired nasal sacs which are independent from the hypophysial tube. In all extant and fossil jawless craniates, the nasal sacs, which contain the olfactory organs, open into a median duct, the nasohypophysial duct, which takes part to the formation of the pituitary gland and either leads postriorly to the pharynx (e.g. in hagfish and galeaspids) or ends as a blind pouch (e.g. in lampreys and osteostracans). In the gnathostomes, this pouch remains as a thin canal in the palate, the buccohypophysial canal, whereas the nasal sacs open separately to the exterior by external nostrils.

The distinguishing character concerns the structure of the paired fins. The fins of the SARCOPTERYGII are fleshy; in these fish the skeleton supporting the fin and its associated musculature project outside the body, thus forming a fleshy base. The fins of the ACTINOPTERYGII are formed by the dermal fin rays; the endoskeleton and musclescontrolling the fins remain within the body.

Basal sarcopterygians may have actually resembled actinopterygian fishes in many ways, but there were some key differences in them that would show up in their descendants. Key among these was the presence of fleshy lobe-fins.

Dipnoans are present today as our "lungfish." They may aestivate (like hibernation only under very hot circumstances) in the mud for long periods of time is a cocoon of mucous. When the rains come, they use their strong appendages to dig out of the mud in which they have been encased.

It seems ironic that these creatures developed their strong, fleshy lobes for movement primarily underwater, on the bottom. Based on recent reports (Gould, 1991; Jarvik, 1996; Zimmer, 1995), the limbs and gross morphology of the basal form Acanthostega were unsuitable for overland travel. Instead, Acanthostega probably propelled itself along the bottom with its limbs or held itself motionless in wait for an ambush. Similar forms included Ichthyostega which possessed seven fingers, and Tulerpeton which probably possessed six. Since moving onto land, vertebrates have mostly reduced their digits to five or fewer. We possess five fingers and toes per appendages, horses have one.

Interestingly, the name Tetrapoda means "four feet," yet snakes, whales, and limbless amphibians are tetrapods. These creatures have simply lost some or all of their limbs. Even when lost, the limbs are not lost uniformly.

Cephalization is the tendency for the head and anatomical units close to the head to form early in ontogeny (life development) and to be well-developed. Cephalization is characteristic of vertebrates and would, therefore, create expectations for patterns in limb development of animals. In most animal embryos, the head and front appendages form first and the lower extremities appear later. This might cause one to assume that if a limb were going to be lost, it would be the hind limbs to be lost because the front limbs appear earlier in ontogeny. Indeed, this is the case in whales where the forelimbs are preserved and the hindlimbs represented by only a vestigal splint for the femur and (in some species) a splint for the femur. This tendency does not hold true, however, in snakes where the hindlimb is represented by a vestigal ilium in primitive forms, but the forelimb is completely absent.

Tetrapods fall into two broad groups, Amphibia and Amniotamorpha. The former is known today from caecillians (amphisbaenians), which are limbless; urodeles (salamanders), which look like amphibian "lizards"; and anurans (frogs and toads). These three groups compose the clade Lissamphibia.

It is difficult to ascertain exactly when and in which group the amniote egg first appeared, but it is believed that diadectomorphs were approaching that condition. It seems likely that these creatures were spending a large amount of their time on land.

As in other vertebrates, nutrients for the developing embryo are stored in theyolk sac, which is much larger in amniotes than in vertebrates generally. Hatchling amniotes also possess an egg-tooth and horny caruncle on the snout tip to facilitate exit from their hard-shelled eggs. The amniotic egg, together with a penis for internal fertilization, loss of a free-living larval stage in the life cycle, and the ability to bury their eggs, enabled amniotes to escape the bonds that confined their ancestors' reproductive activities to aquatic environments.

Some components of the amniotic egg have been variously modified within Amniota. Placental mammals, for example, have suppressed the egg shell and yolk sac, and elaborated the amniotic membranes to enable nutrients and wastes to pass directly between mother and embryo.

Development of extra embryonic membranes in an amniote egg (chick). In this early developmental stage, the yolk sac is expanding over the yolk. The amnion and chorion are expanding over the embryo and will eventually form the amniotic chamber. The allantois is expanding toward the chorion, with which it will form a respiratory membrane, in addition to storing metabolic wastes of the embryo.

The comparative aridity of the terrestrial environment affects all aspects of amniote biology, and not just their reproductive systems. Thus, amniotes have highly keratinized skins that are relatively impervious and reduce water loss. They also possess horny nails that, among other things, enable them to use their forelimbs to dig burrows into which they can retreat during the heat of the day.

The imperative to reduce water loss is equally evident in the density of renal tubules in the metanephric kidney of amniotes, in the larger size of their water-resorbing large intestines, and in the full differentiation of the Harderian and lacrimal glands in the eye socket whose antibacterial secretions help to moisten and, along with a third eyelid (the nictitans), to further protect the eye from desiccation.

The commitment of amniotes to a life on land is also revealed by anextensive system of muscle stretch receptors that enables finer coordination and greater agility during locomotion, their enlarged lungs (which are the only remaining organs of gas exchange owing to the loss of gills), and the complete loss of the lateral line system other vertebrates use to detect motion in water.

Many of these features are rarely preserved in fossils, but there are some novelties in the skeleton that are no less diagnostic of amniotes. For example, amniotes have at least two pairs of sacral ribs, instead of just one pair. They also have an astragalus bone in the ankle, instead of separate tibiale, intermedium, and proximal centrale bones. Finally, they have paired spinal accessory (11th) and hypoglossal (12th) cranial nerves incorporated into the skull, in addition to the ten pairs of cranial nerves present in amphibians.

Perhaps the most famous non-mammalian synapsid is Dimetrodon. This animal was the top predator of the Permian. This genus lived in a variety of environments and would have been probably fed on numerous types of other vertebrates including other "pelycosaurs", the giant "amphibians" like Eryops, and diadectomorphs.

Basal therapsids would appear later with their potentially more advanced metabolisms and would have been able to exploit new environments. It is possible that the basal therapsids were covered with hair. It is unkown whether they would have possessed external ears (pinnae), gave birth to live young (a characteristic independently developed in many vertebrate groups), or even if they had fur. Based on the most primitive extant mammals (prototherians), it may be suggested that basal therapsids at the cynodont level may have lacked external pinnae, laid eggs, and had some form of insulation.

All known early synapsids had a lateral temporal fenestra (a hole in the lateral surface of the skull behind the orbit) that is still present in a modified form in mammals. Primitively, the lateral temporal fenestra was bordered by only three bones.

The occiput was broad and it faced posterodorsally. In other early amniotes, the endochondral bones of the braincase formed a narrower surface, and it was more or less vertical.

The pubis had a long, ridged anterodorsal edge.

Non-mammalian therapsids grew to a variety of sizes and filled many of the ecological niches we find in the world today. Similar in some respects to modern large ungulates were tapinocephalids. Basal theriodonts were similar to similar our terrestiral carnivorans, and many of the smaller forms filled niches that might correspond to our rodents. It was actually the small forms that were able to survive the extinction event that hit many therapsid groups. Ironically it was these small, insectivoran-style therapsids that would eventually give rise to mammals while the hippo- and carnivoran- mimics went extinct.

Basal therapsids may or may not have had "improved" metabolic conditioning. It seem likely that the relatively advanced forms like basal cynodonts might have been advanced well above the common basal amniote metabolism. If this is true, then it is not unreasonable to restore them with some form of insulatory structure; in this case, hair. Tenrecs and basal mammals (i.e., the duckbilled platypus) show the type of metabolism to which I refer. More basal forms may or may not have had more advanced metabolic rates than modern reptiles.

Mammals hear sounds after they are transmitted from the outside world to their inner ears by a chain of three bones, the malleus, incus, and stapes. Two of these, the malleus and incus, are derived from bones involved in jaw articulation in most other vertebrates.

Mammals have hair. Adults of somespecies lose most of their hair, but hair is present at least during some phase of the ontogeny of all species. Mammalian hair, made of a protein called keratin, serves at least four functions. First, it slows the exchange of heat with the environment (insulation). Second, specialized hairs (whiskers or "vibrissae") have a sensory function, letting the owner know when it is in contact with an object in its external environment. These hairs are often richly innervated andwell-supplied with muscles that control their position. Third, through their color and pattern, hairs affect the appearance of amammal. They may serve to camouflage, to announce the presence of especially good defense systems (for example, the conspicuous color pattern of a skunk is a warning to predators), or to communicate social information (for example, threats, such as the erect hair onthe back of a wolf; sex, such as the different colors of male and female capuchin monkeys; presence of danger, such as the white underside of the tail of a white tailed deer). Fourth, hair provides some protection, either simply by providing an additional protective layer (against abrasion or sunburn, for example) or by taking on the form of dangerous spines that deter predators (porcupines, spinyrats, others).

Mammals feed their newborn young with milk, a substance rich in fats and protein that is produced by modified sweat glands called mammary glands. These glands, which take a variety of shapes, are usually located on the ventral surface of females along paths that run from the chest region to the groin. They vary in number from two (one right, one left, as in humans) to a dozen or more.

Other characteristics found in most mammals include highly differentiated teeth; teeth are replaced just once during an individual's life (this condition is called diphyodonty, and thefirst set is called "milk teeth); a lower jaw made up of asingle bone, the dentary; four-chambered hearts, a secondary palate separating air and food passages in the mouth; a muscular diaphragm separating thoracic and abdominal cavities; highly developed brain; endothermy and homeothermy; separate sexes with the sex of an embryobeing determined by the presence of a Y or 2 X chromosomes; and internal fertilization.

The Class Mammalia includes around 5000 species placed in 26 orders (systematists do not yet agree on the exact number or on how some orders are related to others). Mammals can be found in all continents and seas. In part because of their high metabolic rates (associated with homeothermy and endothermy), they often play an ecological role that seems disproportionately large compared to their numerical abundance.

The Primates are an ancient and diverse eutherian group, with around 233 living species placed in 13 families. Most dwell in tropical forests. The smallest living primate is the pygmy mouse lemur, which weighs around 30 g. The largest is the gorilla, weighing up to around 175 kg.

Primates radiated in arboreal habitats, and many of the characteristics by which we recognize them today (shortened rostrum and forwardly directed orbits, associated with stereoscopic vision; relatively large braincase; opposable hallux and pollex; unfused and highly mobile radius and ulna in the forelimb and tibia and fibula in the hind) probably arose as adaptations for life in the trees or are primitive traits that were retained for the same reason. Several species, including our own, have left the trees for life on the ground; nevertheless, we retain many of these features.

Primates are usually recognized based on a suite of primitive characteristics of the skull, teeth, and limbs. Some of these are listed above, including the separate and well-developed radius and ulna in the forearm and tibia and fibula in the hindleg. Others include pentadactyl feet and presence of a clavicle. Additional characteristics (not necessarily unique to primates) include first toe with a nail, while other digits bear either nails or claws, and stomach simple in most forms (sacculated in some leaf-eating cercopithecids). Within primates, there is a tendency towards reduction of the olfactory region of the brain and expansion of the cerebrum (especially the cerebral cortex), correlated with an increasing reliance on sight and increasingly complex social behavior.

The teeth of primates vary considerably. The dental formula for the order is 0-2/1-2, 0-1/0-1, 2-4/2-4, 2-3/2-3 = 18-36. The incisors are especially variable. In some forms, most incisors have been lost, although all retain at least 1 lower incisor. In others, the incisors are intermediate in size and appear to function as pincers or nippers, as they commonly do in other groups of mammals. In some, including most strepsirhines (see next paragraph), the lower incisors form a toothcomb used in grooming and perhaps foraging. In the aye-aye (Daubentoniidae), the incisors are reduced to 1 in each jaw and are rodent-like in form and function. Canines are usually (but not always) present; they vary in size, including within species between males and females. Premolars are usually bicuspid (bilophodont), but sometimes canine-like or molar-like. Molars have 3-5 cusps, commonly 4. A hypocone was added early in primate history, and the paraconid was lost, leaving both upper and lower teeth with a basically quadrate pattern. Primitively, primate molars were brachydont and tuberculosectorial, but they have become bunodont and quadrate in a number of modern forms.

Living primates are divided into two great groups, the Strepsirhini and the Haplorhini. Strepsirhines have naked noses, lower incisors forming a toothcomb, and no plate separating orbit from temporal fossa. The second digit on the hind foot of many strepsirhines is modified to form a "toilet claw" used in grooming. Strepsirhines include mostly arboreal species with many primitive characteristics, but at the same time, some extreme specializations for particular modes of life.
Haplorhines are the so-called "higher" primates, an anthropocentric designation if ever there was one. They have furry noses and a plate separating orbit from temporal fossa, and they lack a toothcomb. Haplorhines include many more species, are more widely distributed, and in most areas play a more important ecological role. Haplorhines are further divided into two major groups, the Platyrrhini and the Catarrhini. Platyrrhines have flat noses, outwardly directed nasal openings, 3 premolars in upper and lower jaws, anterior upper molars with 3 or 4 major cusps, and are found only in the New World (families Cebidae and Callitrichidae).
Catarrhines have paired downwardly directed nasal openings, which are close together; usually 2 premolars in each jaw, anterior upper molars with 4 cusps, and are found only in the Old World (Cercopithecidae, Hylobatidae, Hominidae).

Most primate species live in the tropics or subtropics, although a few, most notably humans, also inhabit temperate regions. Except for a few terrestrial species, primates are arboreal. Some species eat leaves or fruit; others are insectivorous or carnivorous.

Here, we follow Anderson and Jones (1984) in formally dividing living primates into two suborders, the Strepsirhini and the Haplorhini. We differ, however, in that we place humans and their close relatives, the chimpanzee, gorilla, and orang in the family Hominidae.

Technical characters (strepsirhines vs. haplorhines)

Technical characters (teeth)

Technical characters (strepsirhines)

Until recently, most classifications included only humans in this family; other apes were put in the family Pongidae (from which the gibbons were sometimes separated as the Hylobatidae). The evidence linking humans to gorillas and chimps has grown dramatically in the past two decades, especially with increased use of molecular techniques. It now appears that chimps, gorillas, and humans form a clade of closely related species; orangutans are slightly less close phylogenetically, and gibbons are a more distant branch. Here we follow a classification reflecting those relationships. Chimps, gorillas, humans, and orangutans make up the family Hominidae; gibbons are separated as the closely related Hylobatidae.

Thus constituted, the Hominidae includes 4 genera and 5 species. Its nonhuman members are restricted to equatorial Africa, Sumatra and Borneo. Hominid fossils date to the Miocene and are known from Africa and Asia.

Hominids range in weight from 48 kg to 270 kg. Males are larger than females. Hominids are the largest primates, with robust bodies and well-developed forearms. Their pollex and hallux are opposable except in humans, who have lost opposability of the big toe. All digits have flattened nails. No hominid has a tail, and none has ischial callosities. Numerous skeletal differences between hominids and other primates are related to their upright or semi-upright stance.

All members of this family have large braincase. Most have a prominent face and prognathous jaw; again, humans are exceptional. All are catarrhine, with nostrils close together and facing forward and downward. The dental formula is the same for all members of the group: 2/2, 1/1, 2/2, 3/3 = 32. Hominids have broad incisors and their canines are never developed into tusks. The upper molars are quadrate and bunodont; the lowers are bunodont and possess a hypoconulid. The uppers lack lophs connecting labial and lingual cusps and thus, in contrast to cercopithecids, are not bilophodont.

Hominids are omnivorous, primarily frugivorous or folivorous. All but humans are good climbers, but only the orangutan is really arboreal.

Members of this family are well-known for the complexity of their social behavior. Facial expression and complex vocalizations play an important role in the behavior of hominids. All make and use nests. Hominids generally give birth to a single young, and the period of parental care is extended.

Species included in database:

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