Introduction to Evolution Chris Scott, Ph.D.
Echinodermata Cephalochordata ANCESTRALDEUTEROSTOME Chordates Urochordata Notochord Myxini Commonancestor ofchordates Craniates Petromyzontida Head Vertebrates Chondrichthyes Vertebral column Actinopterygii Gnathostomes Jaws, mineralized skeleton Actinistia Osteichthyans Lungs or lung derivatives Lobe-fins Dipnoi Lobed fins Amphibia Tetrapods Reptilia Limbs with digits Amniotes Amniotic egg Mammalia Milk
Derived Characters of Chordates • All chordates share a set of derived characters • Some species have some of these traits only during embryonic development • Four key characters of chordates: • Notochord • Dorsal, hollow nerve cord • Pharyngeal slits or clefts • Muscular, post-anal tail
Dorsal,hollownerve cord Musclesegments Notochord Mouth Anus Pharyngealslits or clefts Muscular,post-anal tail
Tiktaalik the “fishapod" FishCharacters TetrapodCharacters ScalesFinsGills andlungs NeckRibsFin skeletonFlat skullEyes on topof skull Shoulder bones Ribs Scales Neck Head Eyes on top of skull Humerus Ulna Flat skull “Wrist” Elbow Radius Fin Fin skeleton
Tiktaalik could most likely prop itself on its fins, but not walk • The first tetrapods appeared 365 million years ago
Cephalochordata Urochordata Myxini Petromyzontida Chondrichthyes Actinopterygii Actinistia Dipnoi Amphibia Reptilia Mammalia
Mammals are amniotes that have hair and produce milk Mammals have: • Mammary glands, which produce milk • Hair • A high metabolic rate, due to endothermy • A larger brain than other vertebrates of equivalent size • Differentiated teeth
Early Evolution of Mammals • Mammals evolved from reptiliansynapsids • These reptiles arose during the Pennsylvanian Period (310 to 275 million years ago). A branch of the synapsids called the therapsids appeared by the middle of the Permian Period (275 to 225 million years ago). It was over millions of years that some of these therapsids would evolve many features that would later be associated with mammals.
Primates • The mammalian order Primates includes lemurs, tarsiers, monkeys, and apes • Humans are members of the ape group
Derived Characters of Primates • Most primates have hands and feet adapted for grasping, and flat nails
Other derived characters of primates • A large brain and short jaws • Forward-looking eyes close together on the face, providing depth perception • Complex social behavior and parental care • A fully opposable thumb (in monkeys and apes)
Living Primates • There are three main groups of living primates: • Lemurs, lorises, and pottos • Tarsiers • Anthropoids(monkeys and apes, including humans)
The first monkeys evolved in the Old World (Africa and Asia) • In the New World (South America), monkeys first appeared roughly 25 million years ago • New World and Old World monkeys underwent separate adaptive radiations during their many millions of years of separation
New World monkey:spider monkey (a) (b) Old World monkey: macaque
Apes • The other group of anthropoids consists of primates informally called apes • This group includes gibbons, orangutans, gorillas, chimpanzees, bonobos, and humans • Apes diverged from Old World monkeys about 20–25 million years ago
(a) Gibbon (b) Orangutan (c) Gorilla (d) Chimpanzees (e) Bonobos
Last Common Ancestor for Humans and Chimpanzees: 7 Million years ago Lemurs, lorises,and bush babies Tarsiers ANCESTRALPRIMATE New World monkeys Anthropoids Old World monkeys Gibbons Orangutans Gorillas Chimpanzeesand bonobos Humans 20 10 0 60 50 30 40 Time (millions of years ago)
What does Hominin mean? • Hominin is a creature that paleoanthropologists have agreed is human or a human ancestor • Hominins include all of the Homo species (Homo sapiens, H. erectus , H. heidelbergensis), all of the Australopithecines and other ancient forms like Paranthropus and Ardipithecus
Comparison of Hip and Foot Bones longer ape pelvis is adapted for quadrupedal locomotion
Footprints found near Lake Turkana, Kenya, show that human foot shape and gait had been achieved 1.5 million years ago Science, VOL 323, ISSUE 5918, pages 1197-1201 (Feb. 27, 2009) Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya
Science, VOL 323, ISSUE 5918, pages 1197-1201 (Feb. 27, 2009) Early Hominin Foot Morphology Based on 1.5-Million-Year-Old Footprints from Ileret, Kenya
Hominin • Hominin comprises the genera Homo, and the two species of the genus Pan (the Common Chimpanzee and the Bonobo), their ancestors, and the extinct lineages of their common ancestor
Between 1993 and 2003 bones of numerous Ardipithecus ramidus specimens were found in Ethiopia
Ardipithecus ramidus October 1, 2009, paleontologists formally announced the discovery of the relatively complete A. ramidus fossil skeleton first unearthed in 1994. The fossil is the remains, dated 4.4 million years old, of a small-brained 110 lb, 3 foot 11 inch female, nicknamed "Ardi", and includes most of the skull and teeth, as well as the pelvis, hands, and feet. Researchers infer from the form of her pelvis and limbs and the presence of her abductable hallux, that she was a facultative biped: bipedal when moving on the ground, but quadrupedal when moving about in tree branches. Based on enamal thickness the teeth suggest she was an omnivore – her dental makeup is more generalized than those of modern apes
Ardipithecus ramidus http://www.sciencemag.org/content/326/5949/60.2.full Youtube version Visual Reconstruction of Ardi movement
Australopithecus afarensis Nickname: Lucy's species Where Lived: Eastern Africa (Ethiopia, Kenya, Tanzania) When Lived: Between about 3.85 and 2.95 million years ago (900,000 thousand years!) Features: 4 foot 11 inches; 100 lbs; combination of bipedal and tree climbing abilities; small brain; dental structure of omniovore
Early Homo • The earliest fossils placed in our genus Homo are those of Homo habilis, ranging in age from about 2.4 to 1.6 million years • Stone tools have been found with H. habilis, giving this species its name, which means “handy man”
Homo habilis(handy man) • Earliest known species of the hominin group that has the Homo genus • Lived from approximately 2.33 to 1.4 million years ago • Some fossils of H. habilis are found with shaped stone tools • Homo habilishas often been thought to be the ancestor of the more gracile and sophisticated Homo ergaster, which in turn gave rise to the more human-appearing species, Homo erectus. • In 2000 a relatively late 1.44 million-year-old Homo habilisand a relatively early 1.55 million-year-old Homo erectus from the same area of northern Kenya challenged the conventional view that these species evolved one after the other • Instead, this evidence - along with other fossils - demonstrate that they co-existed in Eastern Africa for almost half a million years!
Homo ergaster characteristics • Fossils from 1.9 to 1.5 MYA show a new stage of hominin development • H. ergaster had a bigger brain than H. habilus • H. ergaster had long slender legs with hip structure adapter for walking • H. ergaster fingers were shorter and straighter, implying lack of tree climbing • Sexual diamorphism is reduced • Tooth structure implying more meat eating
Homo erectus Homo erectus (upright man) is an extinct species of hominid that lived about 1.9 million to 143,000 years ago (1.75 million years!!!) The species originated in Africa and spread as far as India, China and Java. Homo erectus, female. Reconstruction based on ER 3733 by John Gurche, front view
Homo erectus Features: average height is 5 foot 9 inches, weight was about 150 lbs; oldest known early humans to have possessed modern human-like body proportions with relatively elongated legs and shorter arms compared to the size of the torso. These features are considered adaptations to a life lived on the ground, indicating the loss of earlier tree-climbing adaptations, with the ability to walk and possibly run long distances. Compared with earlier fossil humans, note the expanded braincase relative to the size of the face. The appearance of Homo erectus in the fossil record is often associated with the earliest handaxes, the first major innovation in stone tool technology.
Homo erectus Range: Generally considered to have been the first species to have expanded beyond Africa, Homo erectus is considered a highly variable species, spread over two continents (it's not certain whether it reached Europe), and possibly the longest lived early human species - about nine times as long as our own species, Homo sapiens, has been around!
Homo heidelbergensis 700,000 – 200,000; first early human species to live in colder climates, it was the first early human species to routinely hunt large animals. This early human also broke new ground; it was the first species to build shelters—creating simple dwellings out of wood and rock.
Homo heidelbergensis • Comparison of Neanderthal and Homo sapiens DNA suggests that the two lineages diverged from a common ancestor, most likely Homo heidelbergensis, sometime between 350,000 and 400,000 years ago – with the European branch leading to H. neanderthalensis and the African branch to H. sapiens
Homo neanderthalensis Homo neanderthalensis was a living species from at least 400,000 to 30,000 million years ago
Homo neanderthalensis • The ancestors of Neanderthals left Africa about 400,000 to 800,000 years ago • Neanderthals evolved over the millennia mostly in what are now France, Spain, Germany and Russia • They were thick-boned with a larger brain (comparable to humans, stronger than humans, they buried their dead, and they made hunting tools • Neanderthals went extinct, or were simply absorbed into the modern human population, about 30,000 years ago