Primate Evolution Miocene Hominoids, and A missing link. Fossil Records, Relative Dating, Absolute Dating, Early Primates, Miocene Hominoids, and A missing link.

Fossil Record The fossil record is not a good representation of all the species that lived on Earth, because not all are preserved or recovered. Hard parts (bones and teeth) preserve better that soft parts(flesh and skin). The chances of fossils increase when remains are buried in a newly forming sediment, especially sediments in swamps, flood plains, river deltas, lakes, and caves. Once remains get buried, chemical conditions also must be right for fossilization to occur.

Fossil Info continued Taphonomy: the study of the processes that affect the remains of dead animals. EX: scattering by carnivores and scavengers and distortion of the remains. The conditions under which fossils are found also influence the fossil record. Ex: Fossils are more likely to be uncovered through erosion in arid areas than in wet areas. The discussions of primate and human evolution must be tentative because the fossil record is limited and spotty. Much is subject to change as knowledge increases.

Dating Paleontology: Is the study of ancient life through the fossil record. Paleo-anthropology: Is the study of ancient humans and their immediate ancestors. These fields have established a time frame,or chronology, for the evolution of life. Scientists use many methods to date fossils. Chronology is established by assigning dates to geologic layers(strata) and to the material remains within them. Dating may be relative or absolute.

Relative Dating Relative Dating establishes a time frame in relation to other strata or materials. Many dating methods are based on the geological study of stratigraphy: the science that examines the ways in which earth sediments accumulate in layers known as strata. In undisturbed strata, age increases with depth. Fossils in a given stratum are younger than those layers below and older than layers above. Remains of animals in plants that lived in the same time are found in the same stratum. Geological Time Scales (Fig 5.1) Fluorine absorption analysis: Bones fossilizing in same ground for the same length of time absorb the same proportion of fluorine from local groundwater.

Absolute Dating This technique is used to date organic remains. A radiometric technique(measures radioactive decay). C14 is an unstable radioactive isotope of Carbon. Cosmic radiation entering the earth’s atmosphere produces C14, and plants take it in as they absorb carbon dioxide. C14 then moves up the food chain as animals eat plants and so on. With depth, the absorption of C14 stops and starts to breakdown. It takes 5,730 years for half of the C14 to change to nitrogen=half life. After another 5,730 only ¼ of the original C14 remains. In another 5,730 only 1/8 and so on. By measuring the proportion of C14 in organic material, scientist can determine a fossil’s date of death. But they can’t use for specimens older than 40,000 years.

Potassium-Argon Technique Used to date specimens from earlier periods. K40 is a radioactive isotope of potassium the breaks down in into argon-40, a gas. The half-life of K40 is 1.3 billion years. This technique can only be used to date inorganic substances: rocks and minerals. K40 in rocks breaks down into Argon 40, which is trapped in the rock until the rock is intensely heated (volcanic activity), at this point the gas may escape. When the rock cools, the breakdown into Argon continues. Dating is down by reheating the rock and measuring the escaping of gas. Cannot be used with material less than 500,000 years old.

Other Dating Methods Other radiometric dating techniques can be used to cross-check K/A dates by using the minerals surrounding the fossils. Uranium series dating: measures fission tracks produced during decay of radioactive uranium into lead. Thermo-luminescence and electron spin resonance techniques measure the electrons that are constantly being trapped in rocks and minerals. Once a date is obtained for a rock found associated with a fossil, the date can also be applied for the fossil.

Early Primates Primates have lived during the last 65 million years, the Cenozoic era. In the beginning of this era, N.America was connected to Europe,but not to S. America. Mostly tropical or subtropical climates. Mesozoic era ended with massive extinction= dinosaurs. Mammals replaced reptiles. Trees and flowering plants proliferated, supplying arboreal foods for primates that evolved to fill niches. Arboreal Theory: primates became primates by adapting to arboreal life.

Visual predation Hypothesis Visual predation hypothesis: The idea that binocular vision, grasping hands and feet, and reduced claws developed because they facilitated the capture of insects, which were prominent in the early primate diet. According to this theory, early primates first adapted to bushy forest undergrowth and low tree branches, where they foraged for insects and fruits. Which means they would have relied heavily on vision.

Early Cenozoic Primates Considerable fossil evidence shows that a diversified group of primates lived in Europe, Africa, Asia and N. America during 2nd epoch of Cenozoic, the Eocene. Eocene= age of the prosimians, two main families. Omomyid family: N. America, Europe, and Asia. Squirrel size, with grasping hands and feet. May be Ancestors to all anthropoids. Adapid family:may be ancestors to lemures. Sometime during Eocene, ancestral anthropoids branched off from the prosimians by becoming more diurnal (active during the day) and by strengthening the trend favoring vision over smell.

Anthropoid traits Anthropoid eyes are roteated more forward when compared with lemurs and lorises. Anthropoids have a fully enclosed bony eye socket. Anthropoids lack a rhinarium, a moist nose continuous with the upper lip. Anthropoids have a dry nose, separate from the upper lip.

Oligocene Anthropoids During Oligocene epoch, 38-23 m.y.a, anthropoids became the most numerous primates. Most evidence found in Egypt’s Fayum deposits, which at the time was tropical rain forest. They lived in trees and ate fruits and seeds. 2 families. Parapithecid family: more primitive and may be ancestral to NW monkeys. Small and similar to marmosets Propliopithecid family: may be ancestral to OW monkeys, apes and humans. Size of a cat. Oligocene was a time of major geological and climatic change. North America and Europe separated. The Great Rift valley of East Africa formed. India drifted into Asia. A cooling trend began. Primates disappeared. h

Miocene Hominoids Earliest hominoid fossils date here (23- 5 m.y.a), which is divided into 3 parts: lower, middle and upper. Earliest hominoid here called proto-apes. Proconsul: genus that represents the most abundant and successful anthropoids of this era. Had teeth similar to modern apes, but skeleton more monkey-like. Skulls more delicate, legs longer than arms. Moved through trees like monkey, lacked capacity for suspension and brachiation. Proconsul probably contained last common ancestor shared by OW monkeys. Middle Miocene, the Proconsul were replaced by OW monkeys and apes. Fossils of Miocene monkeys and prosimians are rare, ape fossils are much more common= forest dwellers and fruit eaters. Late Miocene: Monkeys became most common anthropoid. Could process leaves more effectively= molars.

Dental Formula’s and Traits Propliopithecids share a distinctive dental formula with the later cararrhines: 2.1.2.3, meaning two incisors, one canine, two premolars, and 3 molars. The formula is based on ¼ of the mouth. The more primitive dental formula is 2.1.3.3, which most prosimians and NW monkeys have. Primitive traits: are those passed on unchanged from an ancestor. Molar cusps: bumps on teeth. Primitive number is 6, anthropoids have 4 or 5. Derived traits: are those that develop in a particular taxon after they split from a common ancestor with another taxon.

Afropithecus and Kenyapithecus During mid-Miocene, Afro-Arabia drifted into Eurasia, providing a land connection between the 3 continents Many animals migrated both ways. Proto-apes were the most common primates during mid-Miocene (16-10 m.y.a). 5-cusped molar pattern. Afropithecus : slow moving arboreal ape, with large projecting front teeth. Recent Discovery, Equatorius africanus, more modern than earlier hominoids, suggesting it used the ground more frequently. These 2 are probable stem hominoids: species somewhere on the evolutionary line near the origins of the modern ape group, which are considered too primitive to be the direct ancestors of living apes and humans.

Sivapithecus Middle and late Miocene apes are grouped into 2 families: Ramapithecidae and Dryopithecidae. There are 2 ramapithecid genera: Sivapithecus and Gigantopithecus. Earlier forms of Sivapithecus that lived in Asia may represent the common ancestor of the orangutan and the African apes. Hominids clearly originated from a Miocene ape, but unclear which one.

Gigantopithecus Largest primitive that ever lived. Confined to Asia, persisted for millions of years, from the Miocene until 400,000 years ago. Still here? Bigfoot. Fossil record consists of only jaw bones and teeth. Size is based on ratios. May have been 1,200 pounds and 10 ft tall or 600 lbs and 9 ft. Gigantopithecus co-existed with Home erectus. Most have been a ground-dwelling ape, that probably ate grasses, fruits, seeds, and bamboo. Their molars were adapted to a diet demanding cutting, crushing, and grinding fibrous matter. Flat with thick enamel.

Dryopithicus Lived in Europe during mid-late Miocene. Last Common ancestor of the lesser apes (gibbons and siamangs) and the great apes. 5-cusp and fissure pattern of its molar teeth, known as Y-5 arrangement, which is typical of hominoids in general. The continental drift that created the land bridge between Africa and Eurasia during mid-Miocene also triggered mountain building and climatic change. Cooler, drier climate and grasslands replaced tropical rain forest=stage set for humans, gorillas and chimps.

Oreopithicus Lived 7 to 9 million years ago. Apparently spent much of its time standing upright and shuffling short distances to collect food. Like fruit and vegetation. This mode of locomotion contrasts with those of other fossil living apes, which climb, brachiate,or knuckle walk. Skeletal fossils show the lower body to be intermediate between those of apes and early hominids. Like early hominids, the lower back arched forward, a vertically aligned knee joint, and a similar pelvis. Features for upright walking. Oreopithicus had a unique foot. Its big toe split our 90 degrees from the other toes, probably associated with a short, shuffling stride. Like a tripod.

A missing link?? This idea comes from the “Great Chain of Being”, a theological belief that various entities could be placed in a progressive chain. Humans were a the top, above them stood only angels and divinity. Below humans were African apes. But humans seemed too superior and different from apes. Between the two, there needed to be some form more progressive than apes- the missing link. Humans and apes share a common ancestor- a creature that was like the African Ape in some ways and like humans in others. Over time all three species have evolved and have diverged from one another. Human ancestors almost certainly diverged from those of chimps and gorillas late in the Miocene epoch.

Evolving The evolutionary line leading to orangutans probably split from one leading to humans, chimps, and gorillas around 13 m.y.a. “Hogopans” refers to the ancestral population of late Miocene hominoids that eventually split 3 ways to produce humans, gorillas and chimps. A nickname for the common ancestors of humans and African apes. About 8 m.y.a Hogopans diverged into 3 groups. They split up by occupying different environmental niches. Isolated from one another=leading to speciation. No fossils of Hogopans have yet to be found or recognized. Ouranopithecus lived in Europe 9-10 m.y.a, may be linked to living African apes and hominids.

Evolving continued Because of Miocene finds reported , some scientists are pondering a new scenario for ape and human evolution. During the middle of the Miocene-a land bridge connected Africa to Eurasia. This connection enabled hominids to spread from Africa into Asia and Europe where they diversified into the groups discussed earlier. See pg 157 in text and discuss