Fossil Evidence of Evolution

1. Fossil Evidence of Evolution

2. Big Bang, p. 1 Origin of Earth Modern Humans p. 450, last sentence Life Begins Complex Animal Life Dinosaurs pp. 215-385 Contemporary Scientific History of the Universe 13.7 billion years in 30 volumes -each volume = 450 pages -each page = 1 million years 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

3. What is a fossil? • …physical evidence of an organism that lived long ago. • Examples: skeletons, shells, leaves, seeds, imprints, tracks, and even fossilized feces and vomit. • The vast majority of fossils are the remains of the hardparts of extinct organisms.

4. How do fossils form? • Fossils form when bodyparts or impressions are buried in rock before they decompose. • The evidence is preserved in the rock through geochemicalprocesses. Fossils are not usually the actual bodilyremains. • Fossilization is an extremely rare event. • Most ancientspecies are not represented in the fossil record.

5. What is the fossil record? • …the collection of fossils that represents the preservedhistory of living things on earth. • The fossil record provides the dimensionoftime to the study of life. • It shows that Earth’s organisms have changedsignificantly over extremely long periods of time.

6. (each layer = period of time)

7. The fossil record is not perfect...but: • It abundantly documents continuouschange. • It is sequential in nature. • It contains numerous examples of evolutionarytransitions. • It is continually growing as newfossils are discovered.

8. General Patterns in the Fossil Record • Deeper rock layers were laid down before the layers above them. Thus, fossils in lowerlayers are older than those in upper ones. • Fossils occur in a definite sequentialorder, from species that appear “primitive” to “modern” appearing ones. • The species representing differentlinesofdescent become more similar to each other as they approach their commonancestors.

10. Comparison of the earliest members of four families of odd-toed ungulates. (a) Hyracotherium (Horses) (b) Hyrachyus (Rhinos) (c) Heptodon (Tapirs) (d) Eotitanops (Brontotheres)

11. Fossils document the evolution of the modern camel from ancestral forms existing in much earlier geologic ages. • Because we can consistently trace lineages like this backwards in time, evolutionary descriptions of earth’s history fit the facts of the geologic record.

13. Fossils Form in Sedimentary Rock

14. The Geologic Time Scale Earth’s history is organized into four distinct ages: • Precambrian • Paleozoic • Mesozoic • Cenozoic The boundaries between these major periods of geologic time are defined by major changes in the types of fossils found in the rocks deposited during these eras.

15. Geologic Time Scale See page 337

16. Geologic Time Scale

17. Dating the Fossil Record • The discovery of radioactivity enabled scientists to accurately determine the ages of fossils, rocks, and events in Earth’s past. • Determining the age of a rock involves using minerals that contain naturally-occurring radioactiveelements and measuring the amount of decay in those elements to calculate approximately how long ago the rock formed.

18. Age Determination Using Radioactive Isotopes • Radioactive isotopes are useful in dating geological materials because they convert or decay at a constant, and therefore measurable, rate. • Age determinations using multiple radioactive isotopes are subject to verysmall errors of measurement, now usually less than 1%.

19. Step 1: List ALL of the long-lived radioactive nuclides. • 150Gd 2.1 x 106 no • 152Gd 1.1 x 1015 yes • 153Dy ~1.0 x 106 no • 174Hf 2.0 x 1015 yes • 176Lu 3.5 x 1010 yes • 182Hf 9 x 106 no • 187Re 4.3 x 1010 yes • 190Pt 6.9 x 1011 yes • 192Pt ~1.0 x 1015 yes • 205Pb 3.0 x 107 no • 232Th 1.40 x 1010 yes • 235U 7.04 x 108 yes • 236U 2.39 x 107 yes - P • 237Np 2.14 x 106 yes - P • 238U 4.47 x 109 yes • 244Pu 8.2 x 107 yes • 247Cm 1.6 x 107 no • 10Be 1.6 x 106 yes - P • 40K 1.25 x 109 yes • 50V 6.0 x 1015 yes • 53Mn 3.7 x 106 yes - P • 87Rb 4.88 x 1011 yes • 93Zr 1.5 x 106 no • 97Tc 2.6 x 106 no • 98Tc 1.5 x 106 no • 107Pd ~7 x 106 no • 115In 6.0 x 1014 yes • 123Te 1.2 x 1013 yes • 129I 1.7 x 107 yes - P • 135Cs 3.0 x 106 no • 138La 1.12 x 1011 yes • 144Nd 2.4 x 1015 yes • 146Sm 7.0 x 107 no • 147Sm 1.06 x 1011 yes

20. Step 2: Order Nuclides by half-life • Listing of nuclides by Half-Life • 50V 6.0 x 1015 yes • 144Nd 2.4 x 1015 yes • 174Hf 2.0 x 1015 yes • 192Pt ~1.0 x 1015 yes • 115In 6.0 x 1014 yes • 152Gd 1.1 x 1015 yes • 123Te 1.2 x 1013 yes • 190Pt 6.9 x 1011 yes • 138La 1.12 x 1011 yes • 147Sm 1.06 x 1011 yes • 87Rb 4.88 x 1011 yes • 187Re 4.3 x 1010 yes • 176Lu 3.5 x 1010 yes • 232Th 1.40 x 1010 yes • 238U 4.47 x 109 yes • 40K 1.25 x 109 yes • 235U 7.04 x 108 yes • 244Pu 8.2 x 107 yes • 146Sm 7.0 x 107 no • 205Pb 3.0 x 107 no • 236U 2.39 x 107 yes - P • 129I 1.7 x 107 yes - P • 247Cm 1.6 x 107 no • 182Hf 9 x 106 no • 107Pd ~7 x 106 no • 53Mn 3.7 x 106 yes - P • 135Cs 3.0 x 106 no • 97Tc 2.6 x 106 no • 237Np 2.14 x 106 yes - P • 150Gd 2.1 x 106 no • 10Be 1.6 x 106 yes - P • 93Zr 1.5 x 106 no • 98Tc 1.5 x 106 no • 153Dy ~1.0 x 106 no

21. Step 3: Eliminate nuclides continually produced by ongoing decay processes • Nuclide Half-Life In Nature? • (years) • 50V 6.0 x 1015 yes 144Nd 2.4 x 1015 yes • 174Hf 2.0 x 1015 yes • 192Pt ~1.0 x 1015 yes • 115In 6.0 x 1014 yes • 152Gd 1.1 x 1015 yes • 123Te 1.2 x 1013 yes • 190Pt 6.9 x 1011 yes • 138La 1.12 x 1011 yes • 147Sm 1.06 x 1011 yes • 87Rb 4.88 x 1011 yes • 187Re 4.3 x 1010 yes • 176Lu 3.5 x 1010 yes • 232Th 1.40 x 1010 yes • Nuclide Half-Life In Nature? • (years) • 238U 4.47 x 109 yes • 40K 1.25 x 109 yes • 235U 7.04 x 108 yes • 244Pu 8.2 x 107 yes • 146Sm 7.0 x 107 no • 205Pb 3.0 x 107 no • 247Cm 1.6 x 107 no • 182Hf 9 x 106 no • 107Pd ~7 x 106 no • 135Cs 3.0 x 106 no • 97Tc 2.6 x 106 no • 150Gd 2.1 x 106 no • 93Zr 1.5 x 106 no • 98Tc 1.5 x 106 no • 153Dy ~1.0 x 106 no FACT: Every nuclide with a half-life of less than 80 million years is missing from our region of the solar system, and every nuclide with a half-life of greater than 80 million years is present. Every single one!

22. Intermediate Forms • So many “transitional” fossils have been found that it is often hard to tell when the transition actually occurred. • Actually, nearly all fossils can be regarded as intermediates because they are connections between their ancestors and their descendants.

23. Ichthyostega Acanthostega Tiktaalik Panderichthys Eusthenopteron Example: The Transition to Land ~365 million years ago ? Video ~385 million years ago

24. Direct Ancestor or Close Relative? • Ancestor-descendant relationships can only be inferred, not directly observed. • No matter how long we watch, no two fossils will ever reproduce—we must look for other ways to determine relatedness. • Because geneticallysimilar organisms typically produce similarphysicalfeatures, we can use fossils to help us recognize related species in the history of life.

25. Archaeopteryx: An Intermediate Form Between Reptiles and Birds

27. Archaeopteryx: An Intermediate Form • While considered the earliestbird, it retained many distinctly reptilian features. • A mosaic of 24 distinct anatomical features • 3 bird-like • 17 reptile-like • 4 “intermediate” • Are dinosaurs still alive?

28. Feathered Dinosaurs from the Liaoning Fossil Beds in China Caudipteryx zoui Microraptor gui Sinornithosaurus millenii Mei long Sinosauropteryx prima Video: The Liaoning Forest

29. Reptile to Mammal Transition • In mammals, each half of the lower jaw is a single bone called the dentary; whereas in reptiles, each half of the lower jaw is made up of threebones. • Evolution of this jawarticulation can be traced from primitive synapsids (pelycosaurs), to advanced synapsids (therapsids), to cynodonts, to mammals.

30. Two of the extra lower jaw bones of synapsid reptiles (the quadrate and articular bones) became two of the middle-ear bones, the incus (anvil) and malleus (hammer). • Thus, mammals acquired a hearing function as part of the small chain of bones that transmit air vibrations from the ear drum to the inner ear.

31. Odontochelys semitestacea – 220 mya Evolution of Turtles • Turtles have a shell and no teeth, both unique traits among reptiles. • Scientists predicted that the oldest turtles should show evidence of these changes. • November 2008: The oldest known turtle, Odontochelys, has an incomplete shell and teeth.

32. Ball python Najash Pachyrhachis Eupodophis Evolution of Snakes • Snakes are tetrapods with no legs. • Evolution predicted primitive fossil snakes with evidence of limbs. • Evolution also predicted intermediate forms between lizards and snakes. • Adriosaurus, a fossil lizard with hindlimbs, reduced forelimbs, and an elongated body.

33. Evolution of Bats • Until recently, the oldest known bats in the fossil record, like modern bats, could fly and echolocate. • Scientists long wondered which ability came first, and they predicted the existence of fossil species that had one, but not both, of these abilities. Icaronycteris index ~50 mya Palaeochiropteryx tupaiodon ~47 mya

34. Prediction Confirmed! • Flying evolved first, echolocation came after. • Onychonycteris finneyi isthe most primitive known species of bat • Lacks evidence of echolocation. • Short, broad wings with claws on all five fingers (modern bats have no more than two claws). • Longer hind legs and broader tail than modern bats. • Shorter forearms than modern bats suggest less efficient flying. Onychonycteris finneyi ~52.5 mya

35. Evolution of Whales • The evolution of whales and dolphins is one of the best-documented transitions in the fossil record. • Fossil, morphological, biochemical, vestigial, embryological, biogeographical, and paleoenvironmental evidence all support the inference that whales evolved from four-leggedland-dwellingmammals.

36. The descent of whales from land-dwelling mammals is well documented by transitional fossils. • The tentative reconstruction shown here is based on extensive fossil evidence. • Many of these transitional fossils have features that were exactly what paleontologists had predicted they would find in ancient whales. • For instance, the fossils show transitions in dentition (teeth), the ear canal, the loss of hind limbs, the development of the tail fluke, and the transition of the nostrils to the blowhole.

37. The fossil record shows that whales and dolphins probably evolved from a group of hoofed mammals called Artiodactyls. Evidence suggests that these were the same ancestors of a well-known group of hoofed mammals called Mesonychids. Mesonychids had notched, triangular teeth similar to those of early predatory whales. Paleontologists previously considered Mesonychids ancestral to whales, but they now consider them to be a “sister group” instead. Mesonyx, a primitive mesonychid ~60 million years ago

38. Artist’s visualization of Sinonyx, another primitive Mesonychid

39. Later fossils in the series show the Pakicetids, a group of carnivorous land mammals with peculiarities in the bones of the ear that have only been found in whales. Pakicetid teeth look a lot like those of fossil whales, but are unlike those of modern whales. The shape of their teeth suggests that they were adapted for hunting fish. Pakicetus ~50 million years ago

40. Artist’s visualization of Pakicetus, a Pakicetid

41. Later, a species existed that had front forelimbs and powerful hind legs with large feet that were adapted for paddling. This animal, known as Ambulocetus, may have moved between water and land. Its fossilized vertebrae show that this animal could move its back in a strong up and down motion, which is the method modern whales and dolphins use to swim and dive. It also had a nose adaptation that enabled it to swallow underwater, the ability to hear underwater, and teeth similar to primitive whales. Ambulocetus ~47-48 million years ago

42. Artist’s visualization of Ambulocetus natans

43. A later fossil in the series, Rodhocetus, shows an animal with smaller functional hind limbs and even greater back flexibility. The ankle bones are similar to existing hoofed land mammals such as the hippopotamus. The forefeet of Rodhocetus had hooves on the central digits, but the hind feet had slender toes which may have supported webbing. This suggests that Rodhocetus was predominantly aquatic. Rodhocetus ~46-47.5 million years ago

44. Artist’s visualization of Rodhocetus

45. Maiacetus At about the same time, a species known as Maiacetus also existed. This species had big teeth that were well-suited for catching and eating fish, suggesting that they made their living in the sea. However, other evidence suggests that they may have came onto land to rest, mate, and give birth. ~47.5 million years ago

46. Artist’s visualization of Maiacetus

47. Artist’s visualization of Protocetus

48. Basilosaurus fossils represent a recognizable whale, with front flippers for steering and a completely flexible backbone. This animal had small hind limbs, although they are thought to have been nonfunctional. hind limbs Basilosaurus ~35 - 45 million years ago

49. Artist’s visualization of Basilosaurus

50. Dorudon was a primitive whale that also had small hind limbs. When they were first found in the same deposits as Basilosaurus, the two animals were so similar that Dorudon were thought to be baby Basilosauri. They are, in fact, different species, and now baby Dorudon are also well known. Dorudon ~37 million years ago