Fossils and early primate evolution

1. Fossils and early primate evolution Chapter 6

2. introduction • Over 99% of everything that has ever lived on Earth has gone extinct • Dinosaurs were the dominant species until 65 mya, when an asteroid hit the earth and wiped almost all of them out • This left holes in the ecosystem • One group that survived were the mammals

3. introduction • Review: • What features do mammals have? • Hair on body • Live young • Milk to feed young • Constant body temperature

6. introduction • Fossils have been known of since ancient Greece, and Darwin used them in formulating his theory • William Smith observed strata, or layers of rock that contained extinct life forms • Fossils are a way to document evolution of life on Earth • Phylogeny: evolutionary relationships • Chronology: place in time

7. What are fossils? • Preserved remains of organisms • Most are bones, teeth, and shell, or things easily preserved • MOST THINGS THAT EVER LIVED WERE NEVER FOSSILIZED • This leaves big gaps in the fossil (and evolutionary) record we try to fill in • To fossilize, organism must be immediately covered with sediment, protected from animals, and be in extreme dry or cold conditions

8. What are fossils? • Taphonomy: study of what happens to a fossil from the time it died until it is discovered • Fossils are found in different types of rock • Sedimentary: made from sediments; creates strata • Volcanic: common for hominins; important for dating

9. Limitations in record • The more samples we have, the better we know the fossil record • Some animals well represented, some have only a few samples • Fayum Depression (Egypt) is important for primate fossils • Would primates living in tropical rainforests preserve well?

10. Geologic time • Have to have new perspective of geologic or evolutionary time (millions of years, not day-to-day) • Earth is 4.6 billion years old • We have recorded major changes of Earth into • Eras: Paleozoic, Mesozoic, Cenozoic • Epochs (smaller divisions of eras)

13. Geologic perspective • Also have to remember that geography was not always the same • Millions of years ago all the continents were connected into one mass called Pangaea, so this allowed animals and plants to migrate easily • Plate tectonics gradually broke this up and made the 7 continents we have today

15. Early beginnings • Land animals evolved from aquatic animals • Lungfish had sacs that they could store air in, as well as gills • Also had bones in their fins • They could move from one pond to another • Natural selection pushed some of them on land permanently into land reptiles

16. Amphibians are dependent on water (must lay eggs in it) • Reptiles have an amniote egg, which does not need water  land animals

17. Mammals • After dinosaur extinction, there were different kinds of mammals • Monotremes (mammals that lay eggs) • Marsupials (have a pouch and embryonic young) • Placentals (mammals with internal fetal development) • Monotremes and marsupials are now only in Australia

18. Mammals

19. age • Early thinkers could not fathom the time we measure now • Had to adapt to scientific and mathematical explanations, not biblical ones • **Law of Superposition: the higher the fossil is in strata, the younger it is

21. Dating techniques • There are two methods of dating fossils • Relative: compares fossils and tells age as older or younger in comparison • Absolute (Chronometric): uses measurements, chemicals, and math to get a numeric age frame

22. Relative dating • Stratigraphic correlation: matches physical and chemical makeup of different sites of strata • Ex. If you know the age of volcanic ash, you can date a fossil older or younger depending on its position to ash • Chemical dating: uses chemical changes • Bones absorb flourine from soil; can compare levels to tell which is older or younger

23. Relative dating • Biostratigraphic (Faunal) Dating: if you know when an animal lived, that can help you date the strata and other layers of strata around it • Uses index fossils: animals whose time frame is well-known

24. Example: mammoths are so well-known that they are good index fossils for dating other nearby remains

25. Absolute dating • Relative dating provides an order of what came first, second, later, latest…etc. • Absolute dating gives actual ages (numeric) • Radiocarbon Dating: uses the decaying of carbon (C14) to get age • **only used on things that used to be alive • **only dates back 50,000 years • Would this be helpful for ancient human ancestors?

26. Radiocarbon dating • Carbon is an isotope that changes over time • All living things are made of carbon • When a living thing dies, the carbon starts to decay into nitrogen • Can measure how much carbon has decayed/how much is left • Half-life: the time it takes for half the carbon in the body to decay. 5,730 years

27. Absolute dating • Another method is Radiopotassium or Potassium/Argon Dating: • volcanic rock has potassium isotopes • The potassium decays into argon • If you date the rock, you know the date of the fossil inside it because it was formed when the rock formed • Use the half-life to measure this rate • Half-life is 1.3 billion • **only used on rock, and not living things • **can date much, much older fossils • Is this helpful for dating ancient human ancestors?

28. Molecular dating • DNA is helpful for dating as well • Idea of Molecular Clock: closely related species have more similar DNA • Also trace amount of mutations • Can use genetic DNA and mtDNA to trace ancestry and phylogeny

29. Molecular dating • For example: What do you notice about the placement of humans in the ape phylogeny?

30. Ancient climate • Foaminefera: tiny holes in fossil shells help us understand levels of oxygen in paleoclimate • Help us know what eras were hot and humid and which were cold and dry • How would this affect primate evolution? • Human evolution ? (Revisit these questions after we learn the human ancestors) • Also think how this would affect sea level and therefore migration between land masses

31. Review questions • What is the difference between relative and absolute dating? What are examples? • What types of fossils would be dated with Radiocarbon and what types with Radiopotassium? • How can fossils help us recreate evolutionary relationships, ancient climate, and ancient diet?

32. Part II

33. Fossil Primates • Review of primate features: • Bone protects eyes • Forward-facing eyes with binocular vision • Grasping hands • Nails instead of claws • Large brain • Long gestation and parental invenstment

34. Why Primates? • We know primate features (ch. 5) • Now focus on why and how these evolved in fossil record • Arboreal hypothesis: unique primate features are due to life in trees • Vision for leaping, hands for grasping branches, intelligence for understanding 3D space • But a lot of animals live in trees • Visual Predation Hypothesis: early primates hunted insects and unique traits helped with this • Nails and precision grip to grab bugs, vision to see them

35. Why Primates? • But what role do the features of primates play in finding fruit, the main diet of most primates? • Vision: can see if fruit is ripe from a distance • Grasping toes let them hold on to branches while they picked fruit with hands • Angiosperm radiation hypothesis (angiosperm means flowering plant) • In Cenozoic, primates and fruit evolved together • All three hypotheses give good explanations

37. First Primates? • In Paleocene (between 65-55 million years ago (mya)), the first primates arose • They evolved out of mammals. • …what event happened that led to mammals appearing? • Plesiadapiforms • Adaptive radiation of mammals • Many went extinct, probably because of competition with rodents • Lack many of the primate features, but had nails • Very base of the family tree • Proprimates, or the precursor to the primate line

38. First True Primates? • Euprimates: true primates, have primate features (eyes protected by bone, grasping, nails, larger brain) • Two groups: • 1. Adapids • Ancestors of Prosimians/Strepsirrhine • Resemble lemurs • 2. Omomyids • Ancestors of Anthropoids • Resemble tarsier

39. Anthropoids Evolve • In the Oligocene (35-24 mya), there was rapid cooling of the globe • This changed habitats • Most fossils from this time come from the Fayum site in Egypt

40. Anthropoids Evolve • Two main groups: • 1. Parapithecids • Primitive, early anthropoids • 2-1-3-3, so may be ancestor of modern ______________________ • 2. Propliopithecids • More common group • 2-1-2-3, so ancestor of _______________________ • Aegyptopithecus is called the “dental ape” because he looked like a monkey but had a Y-5 molar

41. Anthropoids Evolve • Two main groups: • 1. Parapithecids • Primitive, early anthropoids • 2-1-3-3, so may be ancestor of modern Platyrrhines • 2. Propliopithecids • More common group • 2-1-2-3, so ancestor of Catarrhines • Aegyptopithecus is called the “dental ape” because he looked like a monkey but had a Y-5 molar

42. Anthropoids Evolve • Parapithecid:

43. Anthropoids Evolve • Propliopithecid (Aegyptopithecus):

44. Anthropoids in South America • Platyrrhines originated in Africa, but are found only in S America today • How did they get there? • Either they migrated across the ocean or through Antarctica (which was much warmer then) • Continents were closer together, oceans may have been lower, land bridges available

45. Apes • Warmer weather accompanied another radiation of primates • Proconsul (20 mya) is an ape ancestor, the first true Hominoid • Ape-like dentition • Adaptations for eating fruit • However, still small and in trees • All four limbs equal length • Not knuckle-walker like apes today

46. Apes Leave Africa • Apes began in Africa and then spread to Europe and Asia • Dryopithecus: Europe, larger body, teeth adapted for fruit, slow growth and development, larger brains, longer arms than legs (modern ape locomotion)

47. Apes Leave Africa • Sivapithecus: • found in Asia • thick enamel for eating tough foods • ancestor of modern orangutans (skulls almost identical to modern orangutans)

48. Apes Leave Africa • Gigantopithecus: • Also in Asia • largest primate to ever live • up to 10 feet tall • teeth adapted for tough food • lived up to time of humans

49. Video • NOVA “First Primates” http://www.pbs.org/wgbh/nova/evolution/first-primates.html

50. Use the following page for a study sheet (the next slide is the same WS you got in class) • Put any useful information under the picture (geography, features, especially who they are ancestors of) • Pg. 183 has a diagram of fossils