Anthropology 150

Evolution of the Primates

Classification and Reconstruction of Evolutionary Relationships

P Phylogenetic Classification  Linnean Terminology

P Homologies and Analogies P Reconstructing Evolutionary Relationships

Phylogenetic Classification The Linnean System

P Kingdom P Phylum P Subphylum P Class P Infraclass P Order P Suborder P Infraorder P Superfamily P Family P Genus P Species P Subspecies

The Linnean System

Carl Von Linne 1707 -1788 OriginallyBased upon Three Criteria:

Body Structure - e.g., the number of limbs, placement of eyes

Body Function B e.g., how an animal gives birth

Sequence of Bodily Growth B e.g. Mammals are distinct from reptiles, placental mammals are distinct from marsupials.

Reconstructing Evolutionary Relationships Homologous Traits are Used as the Basis for Determining

Evolutionary Relationships

P Homologies and Analogies  Homologies are due to common ancestry B Example: all primates share a number of traits, including an emphasis on vision and a decreased sense of smell. All primates have five digits on the hands and feet.

 Analogies are due to convergent evolution B Example: Robust australopithecines and Gorillas B Example: Aquatic mammals and fish

Reconstructing Evolutionary Relationships P Reconstructing Evolutionary Relationships  Classifications reflect shared ancestry  Each split in the phylogenetic tree represents a radiation of the species

P Evolutionary relationships can be reconstructed using fossils.  The fossil record is imperfect, but improving constantly

B The process of fossilization is rare B The geological loci where fossils can be both preserved and discovered are even more rare P Direct genetic or biochemical data can also be used

Classifying Humans

P Kingdom - Animalia P Phylum - Chordata P Subphylum - Vertebrata P Class - Mammalia P Infraclass - Eutheria P Order - Primates P Suborder - Anthropoidea P Infraorder - Catarrhini P Superfamily - Hominoidea P Family - Hominidea P Genus - Homo P Species - Homo sapiens P Subspecies - Homo sapiens sapiens

By Placing Phylogenetic Relationships on a Timeline, we can construct a dynamic evolutionary model

Hominoid Phylogenetic Relationships

Phylogenetic classifications are more than static divisions

Types of Primates

Lemur

Tarsier Chimpanzee Gorilla

Snub-nosed Monkey Mangabey

A Brief History of the Primates Geological Time Scale

PTimescale P Pleistocene 2.5-0.01 Mya Excellent mammal record P Pliocene 5.3-2.5 Mya Very good mammal record P Miocene 24-5.3 Mya Pretty good mammal record P Oligocene 34-24 Mya Spotty mammal record. Many gaps in various lineages P Eocene 54-34 Mya Surprisingly good mammal record, due to uplift and exposure of fossil-bearing strata in the Rockies P Paleocene 67-54 Mya Fair record early on, but late Paleocene is lousy

Climate Trends

A Brief History of the Primates

Primate Origins

P The origins of the primate order are murky. Prior to 65 million years ago (mya) there are few fossils that are certainly primates. P "The modern assemblage can be traced with little question to the base of the Eocene" says Carroll (1988). But before that, the origins of the very earliest primates are fuzzy. There is a group of Paleocene primitive primate-like animals called "plesiadapids" that may be ancestral to primates, or may be "cousins" to primates. (see Beard, in Szalay et al., 1993.) P Primates received their big break circa 65 mya when earth was struck by a meteor. The ensuing global climatic change brought about the extinction of the dinosaurs, which opened up huge ecological niches. An adaptive radiation of the primates followed.

Modern Tarsier

Possible analogue for early primates

The Paleocene Period 67-54 mya

P The earth had a tropical or sub-tropical climate reaching to the polar regions. Evidence suggests that patterns of rainfall my have changed dramatically after the extinction of the dinosaurs, with much higher levels spread more evenly through the seasons of the year. The forests of the Northern American Paleocene seem to have been more dense and swampy than in the late Cretaceous. P Mammals of this era were small. A dense forest habitat favors smaller bodies over large. P Hardly any mammals of this period have teeth that would suggest a leaf- eating diet. Most seem to have either been insect eaters or generalists, perhaps adding fruits, berries and shoots. P Some scholars believe that here are a few fossils of this period that may represent early primates. There are some fragments of jars and teeth representing species that are lemur-like in size. Other scholars doubt whether these are true primates, however.

Early Primate Fossils

The Eocene Period 54-34 mya

P Toward the end of the Paleocene and until about 50 mya the global climate became noticeably warmer. The range of tropical vegetation expanded, pushing the paratropical rainforest inside the Arctic Circle, creating the unusual situation of jungles at the poles. P Many present-day orders emerged in the early Eocene. Many other archaic mammals of the Paleocene continued, but became extinct by the end of the epoch. P First evidence of primate divergence: Lemur-like adapids diverge from tarsier-like omomyids. P The Late Eocone represents the peak in global temperatures for the Tertiary. During the Middle and Late Eocene a cooler and drier trend was particularly marked in higher latitudes, where winter frosts may have been felt later in the Eocene. About 34 mya the downhill trend grew suddenly steeper. In less than 1 million years, northern latitudes experienced a plunge in annual temperatures and a great increase in seasonal range. P Many primates, esp. those at northern latitudes became extinct at this time. As deciduous trees replaced evergreens, they lost their primary source of food. P In the primate line, the split between anthropoids and prosimians occurs in the late eocene. The anthropoids include monkeys and apes, the larger primates. The prosimians are smaller primates like the lemurs and the tarsiers.

Oligocene 34-24 34-24 mya

P The new world monkeys separated from the line that leads to the Old World Monkeys and apes. P In the later half of the Oligocene, the fossil record improves dramatically. One of the more spectacular fossil locations is El Fayum, located just south of modern day Cairo. P During the early Oligocene there were no primates in N. America or Europe; it was too cold. P Haplorhines (sub-order that includes monkeys and apes) become numerous and diverse. P The first secure member of the cattarhine infraorder (ancestral to old world monkeys and apes) is Aegyptopithecus B molars are ape-like. Skull 3-4 inches long, big canines. Good vision. Large visual cortex and smaller olfactory lobes. It is ancestral to both old world monkeys and apes, but not to NW monkeys. It has 2 premolars, not 3.

Aegyptopithecus from El Fayum, Egypt

The Miocene Period 24-5.3 mya

P The early miocene saw the beginnings of a shift toward a warmer and considerably drier climate. Geological changes, such as the opening of Drake's passage, and tectonic uplift that fomred many of today's great mountain ranges, altered patterns of air and ocean circulation, bring about changes in global climate and rainfall, and therefore in the vegetation pattern. P Warming in the middle latitudes brought some expansion of the tropical and semi-tropical forest, but the drying trend encouraged a new vegetative type, the chapparl, or thorn scrub. P The connection between Africa and Eurasia enabledd african fauna to emigrate into Asia, including primates. P After the middle Miocene, apparently the warmest part of the whole period from 35 mya to the present, the world became a cooler, drier place. The arctic Ocean became connected to the Atlantic, which increased the colder deep waters of the Atlantic.

Monkeys and Apes • In addition to habitat change, there is another explanation for the

passing of the great diversity of apes seen in the early and middle Miocene. It is the evolutionary diversification of a related group of primates, the monkeys. Monkeys are in general smaller than living apes, they usually have tails, their molar teeth are pushed up into transverse crests called lophs, and their brains are relatively smaller than apes' brains. The distinction between monkeys and apes is still muddled in the popular mind

• The evolutionary distinction between apes and monkeys is sharp, however. The earliest monkeys are singular species with lophed molar teeth that appear in the early Miocene. They must have lived surrounded by trees teeming with different species of early apes. The apes had dominated the primate ecological spectrum since the Oligocene, when they and the monkeys had last shared a common ancestor. The apes had won the first round, but by the middle to late Miocene it was the monkeys' turn.

Miocene Apes

P Monkeys split from apes early in the Miocene (after aegyptopithecus). We have many shared anatomical characteristics with chimps and other apes:  Lack of a tail. Generally large body size, shortened trunk, stable spine, and the position and musculature of the shoulder joing.  True Brachiation: the ability to rotate the arm to allow swinging arm over arm under the branches of trees. Originally an adaptation to feeding at the end of branches. Monkeys have limited arm mobility and display what can be called "semi-brachiation." Should joint oriented upward; upper body is fairly erect.  The rigid trunk facilitiates some degree of bi-pedalism. Strictly speaking, chimps and non-human apes are quadripedal, but they do walk upright for limited periods of time. Chimps and gorillas often use a form of locomotion called knuckle-walking.  Finally, we can mention larger brains. Relative to body size, all apes have larger brains than other primates and the monkeys. This is probably the most important.

Miocene Apes Proconsul

P The first Miocene ape in Africa is proconsul ( a genus with four species). Proconsul is clearly closer to a chimp than a monkey, so it post-dates the splits of monkeys from apes. Range in size from baboon to gorilla size may be sexual dimorphism. Lots of specimens; it was very successful. The best known specimen is slightly smaller than a chimp; hominoid dentition (Y5) and relatively large brain compared to body size. It's post-cranial skeleton is quadrapedal, with grasping hind feet. P Proconsul displays clear ape-like dentition. P Relationship to Ramapithecus is uncertain, Ramapithecus probably ancestral to orangutans.

Proconsul

Middle Miocene Apes Descendants of Proconsul

P Proconsul gives rise to Kenyapithecus in Africa and Dryopithecus in Europe and Asia P In Asia, the Dryopithecines evolve into Ramapithecus, Sivapithecus, and eventually the organgutans. P In Africa, Kenyapithecus is clearly ancestral to later apes, including gorillas,

chimps and humans. Kenyapithecus was a knuckle-walker (McCrossin et al), clearly showing that the hominid line passed through a universal knuckle- walking stage. P Kenyapithecus has been split into a primitive genus (Kenyapithecus) and an advanced lineageage (Equatorious). Equatorious apparently leads to gorillas, chimps, and humans.

The Asian Apes - The Ramapithecines

Modern Orangutan Descendant of Sivapithecus

Late Miocene Apes

P Unfortunately, the late Miocene fossil record is very bad. P It is clear that the African Apes (the hominoids) diversify. P The modern African apes (Gorillas, chimpanzees, humans) diversify during this time. P Humans are most similar to chimpanzees, so we assume that gorillas split first P The split between hominids (the line ancestral to humans) and chimpanzees occured sometime between 7 and 5 mya. This date is suggested by both the fossil records and DNA/biochemical studies.

Hogopans?

Modern African apes are resticted to three genera: Gorilla Pan Homo

These three genera last shared a common ancestor about 8-6 mya

Differences and similarities between Chimpanzees and Gorillas

• Both species display knuckle walking for locomotion

• Both sleep in trees • Gorillas are larger overall and have greater

sexual dimorphisms • Gorillas eat more tough vegetable matter • Distinctive social organization and mating

patterns • Differences in tool use

Western Apes vs. Eastern Apes

Homoids, Hominids, and Hominins