What is evolution? Transitional fossils: evidence for evolution. In its broadest sense, evolution is simply the change in life through time.

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1 Transitional fossils: evidence for evolution of- darwin.deviantart.com/art/no- Transitional- Fossils Western MA Atheists and Secular Humanists 28 May 2016 What is evolution? In its broadest sense, evolution is simply the change in life through time. An Early Jurassic scene 1

2 Geologists have known for centuries that life changed over time: in the earlier periods of the world, the less complex and less perfect tribes of animals and plants greatly predominated, and the more perfect species became more and more numerous up to the creation of the present races. Edward Hitchcock, 1847 This is today known as the Principle of Faunal Succession. Notice how Hitchcock explained faunal succession: more perfect species became more and more numerous up to the creation of the present races. He thought that there were multiple creations, and the story in Genesis explained only the origin of present life forms. He had to do this to square his Christianity and geology. creation- story.jpg 2

3 Darwin had a very different understanding of why faunal succession occurred: these several facts accord well with our theory Charles Darwin, 1859 He considered it to be among the observations supporting biological evolution. of- young- Charles- Darwin.jpg Today, evolution is understood to be the change in heritable traits in biological populations over time. content/uploads/2011/04/evolution- Of- Man- Parodies- 333.jpg 3

4 A major reason for such change is natural selection, the process by which genetic variation changes depending on its benefit to a population. Traits that enhance survival and reproduction increase in populations. Traits that hinder survival rates decrease. Natural selection results from three basic facts: 1. Heritable variations exist 2. Organisms produce more offspring than can live 3. Offspring vary in ability to survive and reproduce Frog with eggs This gives rise to competition for resources among offspring. 4

5 What evidence is there for evolution? The evidence is derived from a variety of sources: 1. The fossil record 2. Comparative anatomy 3. Artificial selection 4. Embryology 5. Geographical distribution Yeah right, evolution is just a theory! ww.zazzle.com Dictionary.reference.com 5

6 9/18/16 Some other objections... Evolution is at odds with literal scripture readings. Some religions are thus hostile to evolutionary theory. Hostility is not restricted to Christianity. Religious literature challenging evolution describes it as unscientific and offers evidence- based reasons for rejecting it. But are these reasons sound? Richard Dawkins content/uploads/sites/6052/2014/12/ evolution- richard- dawkins- quote- 2.jpg 6

7 9/18/16 Evolution is a scientific theory and can be tested. It hasn t failed any yet! Further, each of the statements challenging it can be tested. Is this really what the fossils say? 7

8 9/18/16 Transitional forms and fossils Chimera greek- mythology jpg Transitional fossils are remains of organisms that share traits both with their ancestors and with their presumed descendant group. A few transitional species: Early tetrapods show traits similar to fish ma 365ma content/ichthyostegaacanthostega.jpg 8

9 Early whales show characteristics, including legs, of their terrestrial ancestors. Ambulocetus: ma f Basilosaurus: ma content/blogs.dir/435/files/2012/04/i- 02d46f31d479f0d5ca2e811cfb2e4d74- dorudon- newpaper.jpg Horses have gotten larger, lost toes, and changed their diet throughout time. 9

10 One of the most famous transitional fossils is Archaeopteryx, the first bird. It was first found in 1861 in Germany. It is now known from 12 skeletons and a single feather. Archaeopteryx skeleton Feather, Wellnhofer (2004) Archaeopteryx has similarities to both theropod dinosaurs and modern birds. Archaeopteryx Modern bird feathered- archaeopteryx.jpg 10

11 Defining birds Birds were once defined as flying animals with feathers. A A A Contour feather- symmetric vane A B B B Downy feather Flight feather- asymmetric vane B The discovery of dinosaurs, such as Microraptor (below), with feathers demands we revise the definition of what a bird is. So what are birds? gui.jpg 11

12 Today, modern birds are defined by a number of unique characters associated with flight: Large eyes and brain They have large eyes and and a large brain. They also lack teeth. Toothless beak The hand is fused into a bone called a carpometacarpus. II III Carpometacarpus I Ankle Tarsometa- tarsus The bones between the ankle and toes are fused into a single bone called a tarsometatarsus. Sacral vertebrae are fused into a bone called a synsacrum. Pygostyle Toes Tail is reduced to a few vertebrae called a pygostyle. Synsacrum 12

13 Other important, but not defining, characters include pneumaticized bones for air sacs and a keeled sternum for flight attachment muscles. Fig Keel Archaeopteryx feather, Wellnhofer (2004) The most obvious trait Archaeopteryx shares with modern birds is the presence of flight feathers. Crow feather Pigeon Archaeopteryx Wellnhofer (2004) 13

14 Archaeopteryx and birds show other traits that indicate a close relationship: Knee Enlarged braincase Very long arms Narrow face Fibula Tibia Archaeopteryx Modern birds Reduced fibula (one of the shin bones) Ankle Aviale Pigeon The group formed from Archaeopteryx and modern birds is termed the Aviale. However, Archaeopteryx s skeleton is much less advanced than those of modern birds: The upper and lower jaws still have teeth. Teeth The hand and foot lack the fused bones of modern birds. Separate tarsals Separate fingers 14

15 Additionally, there is a long, bony tail, Small keel there is no synsacrum, and there is only a small keel on the sternum. This last character suggests that its flight was not as strong as a modern bird. Unfused sacral vertebrae Bony tail Archaeopteryx as a dinosaur Antorbital fenestra Dinosaurs belong to a group of reptiles called archosaurs, which have antorbital fenestrae. Archaeopteryx also had the fenestra, indicating it was an archosaur. Antorbital fenestra 15

16 Among archosaurs, only dinosaurs had a hollow hip socket, called a perforate acetabulum. Perforate acetabulum Archaeopteryx also had this feature and must have been a dinosaur. Among dinosaurs only theropods had a three- fingered hand with pits on the finger bones. Allosaurus hand Archaeopteryx has a three- digit hand with pits on the finger bones, making it a theropod. Pitted metacarpals Large hand 16

17 Among theropods, only Maniraptorans had a wrist bone, a semilunate carpal, that allowed the hands to fold against the arm. Semilunate carpal Velociraptor skeleton.jpg Semilunate carpal Archaeopteryx also had semilunate carpal, making it a Maniraptoran. Maniraptorans and Archaeopteryx share a number of other characters, including: Velociraptor Backward pointed pubis skeleton.jpg a backward pointed pubis, No front projection a missing front part of pubic boot, Typical theropod pelvis with pubic boot with front and back projections 17

18 and a bowed, or bent, ulna (one of the lower arm bones). Bent ulna skeleton.jpg The most closely related dinosaurs to Archaeopteryx are the Dromaeosaurs, also known as the raptors. We now know that Velociraptor was actually feathered. img.com/gawker- media/image/upload/nqqj6dhufzow02u1d5f7.jpg Pigeon ulna with quill knobs 18

19 Is Archaeopteryx a transitional fossil? Transitional fossils are remains of organisms that share traits both with their ancestors and with their presumed descendant group. Ancestor trait Long tail Teeth Three separate fingers No fused foot bones No fused hips Descendant trait Flight feathers Long arms Enlarged braincase Narrow face Reduced fiblua Archaeopteryx fits the definition! How do creationists deal with Archaeopteryx? 19

20 9/18/16 What about the following statement? It should be apparent that this statement is false based on the fossil evidence! It also shows a lack of understanding of fossilization in general. Fossil skeletons are often rare in well- oxygenated environments, which promote decay, and in acidic environments, which dissolve bones. Dinosaur bone casts 20