Fossil Evidence of Evolution

Transcription

1 Fossil Evidence of Evolution

2 Contemporary Scientific History of the Universe Big Bang, p billion years in 30 volumes -each volume = 450 pages -each page = 1 million years Origin of Earth Life Begins Complex Animal Life Dinosaurs pp Modern Humans p. 450, last sentence

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 hard parts of extinct organisms.

4 How do fossils form? Fossils form when body parts or impressions are buried in rock before they decompose. The evidence is preserved in the rock through geochemical processes. Fossils are not usually the actual bodily remains. Fossilization is an extremely rare event. Most ancient species are not represented in the fossil record.

5 What is the fossil record? the collection of fossils that represents the preserved history of living things on earth. The fossil record provides the dimension of time to the study of life. It shows that Earth s organisms have changed significantly over extremely long periods of time.

6 (each layer = period of time)

7 The fossil record is not perfect...but: It abundantly documents continuous change. It is sequential in nature. It contains numerous examples of evolutionary transitions. It is continually growing as new fossils are discovered.

8 General Patterns in the Fossil Record Deeper rock layers were laid down before the layers above them. Thus, fossils in lower layers are older than those in upper ones. Fossils occur in a definite sequential order, from species that appear primitive to modern appearing ones. The species representing different lines of descent become more similar to each other as they approach their common ancestors.

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10 Comparison of the earliest members of four families of oddtoed 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.

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13 Fossils Form in Sedimentary Rock

14 The Geologic Time Scale Earth s history is organized into four distinct ages: 1. Precambrian 2. Paleozoic 3. Mesozoic 4. 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 radioactive elements 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 very small errors of measurement, now usually less than 1%.

19 Step 1: List ALL of the long-lived lived radioactive nuclides. 10 Be 1.6 x 10 6 yes - P 40 K 1.25 x 10 9 yes 50 V 6.0 x yes 53 Mn 3.7 x 10 6 yes - P 87 Rb 4.88 x yes 93 Zr 1.5 x 10 6 no 97 Tc 2.6 x 10 6 no 98 Tc 1.5 x 10 6 no 107 Pd ~7 x 10 6 no 115 In 6.0 x yes 123 Te 1.2 x yes 129 I 1.7 x 10 7 yes - P 135 Cs 3.0 x 10 6 no 138 La 1.12 x yes 144 Nd 2.4 x yes 146 Sm 7.0 x 10 7 no 147 Sm 1.06 x yes 150 Gd 2.1 x 10 6 no 152 Gd 1.1 x yes 153 Dy ~1.0 x 10 6 no 174 Hf 2.0 x yes 176 Lu 3.5 x yes 182 Hf 9 x 10 6 no 187 Re 4.3 x yes 190 Pt 6.9 x yes 192 Pt ~1.0 x yes 205 Pb 3.0 x 10 7 no 232 Th 1.40 x yes 235 U 7.04 x 10 8 yes 236 U 2.39 x 10 7 yes - P 237 Np 2.14 x 10 6 yes - P 238 U 4.47 x 10 9 yes 244 Pu 8.2 x 10 7 yes 247 Cm 1.6 x 10 7 no

20 Step 2: Order Nuclides by half-life life Listing of nuclides by Half-Life 50 V 6.0 x yes 144 Nd 2.4 x yes 174 Hf 2.0 x yes 192 Pt ~1.0 x yes 115 In 6.0 x yes 152 Gd 1.1 x yes 123 Te 1.2 x yes 190 Pt 6.9 x yes 138 La 1.12 x yes 147 Sm 1.06 x yes 87 Rb 4.88 x yes 187 Re 4.3 x yes 176 Lu 3.5 x yes 232 Th 1.40 x yes 238 U 4.47 x 10 9 yes 40 K 1.25 x 10 9 yes 235 U 7.04 x 10 8 yes 244 Pu 8.2 x 10 7 yes 146 Sm 7.0 x 10 7 no 205 Pb 3.0 x 10 7 no 236 U 2.39 x 10 7 yes - P 129 I 1.7 x 10 7 yes - P 247 Cm 1.6 x 10 7 no 182 Hf 9 x 10 6 no 107 Pd ~7 x 10 6 no 53 Mn 3.7 x 10 6 yes - P 135 Cs 3.0 x 10 6 no 97 Tc 2.6 x 10 6 no 237 Np 2.14 x 10 6 yes - P 150 Gd 2.1 x 10 6 no 10 Be 1.6 x 10 6 yes - P 93 Zr 1.5 x 10 6 no 98 Tc 1.5 x 10 6 no 153 Dy ~1.0 x 10 6 no

21 Step 3: Eliminate nuclides continually produced by ongoing decay processes Nuclide Half-Life In Nature? (years) 50 V 6.0 x yes 144 Nd 2.4 x yes 174 Hf 2.0 x yes 192 Pt ~1.0 x yes 115 In 6.0 x yes 152 Gd 1.1 x yes 123 Te 1.2 x yes 190 Pt 6.9 x yes 138 La 1.12 x yes 147 Sm 1.06 x yes 87 Rb 4.88 x yes 187 Re 4.3 x yes 176 Lu 3.5 x yes 232 Th 1.40 x yes Nuclide Half-Life In Nature? (years) 238 U 4.47 x 10 9 yes 40 K 1.25 x 10 9 yes 235 U 7.04 x 10 8 yes 244 Pu 8.2 x 10 7 yes 146 Sm 7.0 x 10 7 no 205 Pb 3.0 x 10 7 no 247 Cm 1.6 x 10 7 no 182 Hf 9 x 10 6 no 107 Pd ~7 x 10 6 no 135 Cs 3.0 x 10 6 no 97 Tc 2.6 x 10 6 no 150 Gd 2.1 x 10 6 no 93 Zr 1.5 x 10 6 no 98 Tc 1.5 x 10 6 no 153 Dy ~1.0 x 10 6 no FACT: Every nuclide with a half-life life of less than 80 million years is missing from our region of the solar system, and every nuclide with w a half-life 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 Example: The Transition to Land Ichthyostega Acanthostega ~365 million years ago Tiktaalik Panderichthys Eusthenopteron? Video ~385 million years ago

24 But wait!! A recent discovery in Poland shows what appear to be tetrapod footprints in rocks that are nearly 400 million years old, pushing back the origin of tetrapods by nearly 20 million years! These are footprints only. No skeletal remains have been described. This discovery, if confirmed, would force a reassessment our understanding of the evolutionary appearance of tetrapods. Video

25 ~365 million years ago Acanthostega Ichthyostega Tiktaalik Panderichthys ~385 million years ago ~400 million years ago

26 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 genetically similar organisms typically produce similar physical features, we can use fossils to help us recognize related species in the history of life.

27 Archaeopteryx: An Intermediate Form Between Reptiles and Birds

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29 Archaeopteryx: An Intermediate Form While considered the earliest bird, 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?

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

31 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 three bones. Evolution of this jaw articulation can be traced from primitive synapsids (pelycosaurs), to advanced synapsids (therapsids), to cynodonts, to mammals.

32 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.

33 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. Odontochelys semitestacea 220 mya

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

35 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

36 Prediction Confirmed! Flying evolved first, echolocation came after. Onychonycteris finneyi is the 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

37 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-legged land-dwelling mammals.

38 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.

39 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

40 Artist s visualization of Sinonyx, another primitive Mesonychid

41 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

42 Artist s visualization of Pakicetus, a Pakicetid

43 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

44 Artist s visualization of Ambulocetus natans

45 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 ~ million years ago

46 Artist s visualization of Rodhocetus

47 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

48 Artist s visualization of Maiacetus

49 Artist s visualization of Protocetus

50 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

51 Artist s visualization of Basilosaurus

52 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

53 Artist s visualization of Dorudon

54 Evolution of Modern Whales Toothed whales have full sets of teeth throughout their lives. Baleen whales only possess teeth during an early fetal stage and lose them before birth. Fossil evidence indicates that the ancient whale Janjucetus, with skull features that make it the earliest known baleen whale, also had a full set of teeth.

55 Artist s visualization of Janjucetus

56 Both Teeth and Baleen? The skull of an ancient toothed whale called Aetiocetus has holes for blood vessels that were likely used to nourish baleen.

57 Artist s visualization of Aetiocetus

58 Evolution of the Blowhole Nostrils at front of skull Nostrils further back Nostrils at middle of skull Nostrils at top of skull Transitional Forms? Pakicetus ~50 million years ago Rodhocetus ~47 million years ago Aetiocetus ~25 million years ago Beluga Whale Today

59 Evolution of Echolocation Fossils demonstrate that whales acquired underwater hearing in stages. Pakicetus lacked the fat pad extending to the middle ear which modern whales have. Basilosaurus, transmitted sound to the middle ear as vibration from the lower jaw. Today s toothed whales can echolocate, the melon directs sound outward and the lower jaw works as a receptor. Melon Pakicetus ~50 million years ago Basilosaurus ~35-45 million years ago Tursiops Bottle-nosed Dolphin

60 Giving Birth Modern whales are born tail first to prevent drowning in the birth canal. Fossil evidence shows a Maiacetus baby with its head facing the birth canal, suggesting that this species still gave birth on land.

61 Other Transitional Fossil Series Primitive fish to sharks and rays. Primitive fish to bony fish. Amphibians to reptiles. Land mammals to manatees. Five-toed ancestors to horses. Bipedal apes to humans.

62 Conclusion Many critical gaps in our knowledge remain. These gaps may or may not be filled by new evidence in the future. However, it is certain that important discoveries will continue to be made that will likely intrigue us, possibly surprise us, and definitely enrich our understanding of the evolutionary history of life.