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Evidence for Evolution

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Evidence for Evolution Fossils Examples Genetics Refs Unit 2: Transmission Genetics Lecture 2.6: Evidence for Evolution John D. Nagy BIO 181: General Biology for Majors, Scottsdale Community College 2020 Revision John Nagy Lec 2.6: Evidence for Evolution 1/36 Fossils Examples Genetics Refs Outline 1 Some interesting fossils Synapomorphies Body plan Vestiges Timeline 2 Examples Mammals Avians Tetrapods 3 Molecular Genetic Evidence 4 Literature cited John Nagy Lec 2.6: Evidence for Evolution 2/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline What kind of creature is this? John Nagy Lec 2.6: Evidence for Evolution 3/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Indohyus \Indohyus was an animal similar in size to a cat but quite different from a cat in shape. It had a long snout and a long tail and long slender limbs. At the end of each limb, there were four or five toes that ended in hoof, similar to that of a deer" [11, pg. 274]. The ear bones have a \thickened wall. called the involucrum [which] is present in all cetaceans, fossil and recent. The involucrum is not present in other mammals, except for one: Indohyus" [11, pg. 275]. John Nagy Lec 2.6: Evidence for Evolution 4/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Ventral (underneath) view of dog cranium The ear bones Thewissen et al. [11] refer to are auditory bullae. So Indohyus is a racoon-shaped mammal with hooves like a deer and ear bones like a whale. John Nagy Lec 2.6: Evidence for Evolution 5/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline What kind of creature is this? John Nagy Lec 2.6: Evidence for Evolution 6/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Ambulocetus Ambulocetus was \roughly the size of a large male sea lion" [11, pg. 279]. \Toes are terminated by a short phalanx carrying a convex hoof" [12, pg. 211]. \The [auditory] bulla has a thick and massive involucrum on its medial side" [9, pg. 726]. `[T]the lower jaw and the auditory bulla have a bony contact unlike any other cetacean" [9, pg. 726]. John Nagy Lec 2.6: Evidence for Evolution 7/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Ambulocetus \In hunting behavior, Ambulocetus may have been similar to a modern crocodile, and, externally, Ambulocetus may have looked like a crocodile" [11, pg. 279] John Nagy Lec 2.6: Evidence for Evolution 8/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Ventral view of. what is that? Where are the auditory (tympanic) bullae? John Nagy Lec 2.6: Evidence for Evolution 9/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Ventral view of bottlenose dolphin (Tursiops truncatus) The auditory bullae have fallen off. They are not attached to the skull. John Nagy Lec 2.6: Evidence for Evolution 10/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Cetaceans have weird, unique ears Cetacean auditory bullae are unique because they are are very thick on one side; they have an involucrum (red arrows); not attached or poorly attached to the skull. (A) and (B): Fossil baleen whales; (C): Fin whale; (D): Right whale; (E) and (F): Fossil toothed whales. John Nagy Lec 2.6: Evidence for Evolution 11/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Summary of observations so far Shared traits collect species naturally into groups: Indohyus and Ambulocetus all had hooves, like the rest of the Artiodactyla (group including hoofed mammals with an even number of toes). Indohyus, Ambulocetus and the rest of the Cetacea (whales, dolphins and porpoises) had thick auditory bullae with in an involucrum. Definition: Synapomorphy Shared, derived characters like these group organisms into natural catagories. They are called synapomorphies. John Nagy Lec 2.6: Evidence for Evolution 12/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Another interesting fossil|Basilosaur These species \have a nasal opening that has shifted back far toward the eyes to form a blowhole and have flippers for forelimbs, a fluke at the end of the tail" [11, pg. 283-4]. John Nagy Lec 2.6: Evidence for Evolution 13/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Look at the front limbs|Hand or flipper? John Nagy Lec 2.6: Evidence for Evolution 14/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Compare to modern northern right whale John Nagy Lec 2.6: Evidence for Evolution 15/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Body plans for different functions are the same John Nagy Lec 2.6: Evidence for Evolution 16/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline What is this? John Nagy Lec 2.6: Evidence for Evolution 17/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Basilosaurs|whales with feet \The hind limbs of basilosaurids retain. the femur, [patella], tibia, fibula, tarsals, metatarsals, and phalanges. However, [they] are greatly reduced in size and the pelvis is not attached to the vertebral column, making the hind limbs unsuitable to support the body weight of these whales" [11, pg. 284] (Image from [2]). John Nagy Lec 2.6: Evidence for Evolution 18/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Modern whales have hind limb bones, but no legs Definition: Vestigial trait A body part that is imperfectly formed and unable to function properly is called vestigial. John Nagy Lec 2.6: Evidence for Evolution 19/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline What kind of creature is this? John Nagy Lec 2.6: Evidence for Evolution 20/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline It's one of these Pantropical spotted dolphin (Stenella attenuata) mother and baby. What happened to the hind limbs in the embryo? Note that in the Cargegie State 17 embryo, hind limb buds are regressing. Hind limbs are vestigial. John Nagy Lec 2.6: Evidence for Evolution 21/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline In addition to gills and hind limbs, embryonic dolphins develop whiskers like a cat's. These are all examples of vestigial traits. Image from [11, pg. 273]. John Nagy Lec 2.6: Evidence for Evolution 22/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Lay the fossils out in time Lay the species out in chronological order based on the earliest known fossils of each type. When we do, we see the following patterns: All are connected by a synapomorphic trait: involucrums on their auditory bullae. They appear to be a single lineage changing through time: The hind limbs are becoming detached from the spine and reduced (vestigial). The auditory bullae are becoming more detached from the skull. They are becoming more aquatic. John Nagy Lec 2.6: Evidence for Evolution 23/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline Transitional fossils If this hypothesis of change through time were true, we should find transitional fossils. And we do. Pakicetus: Hooves, involucrum, other cetacean characteristics [1]. Maiacetus: Involucrum, other cetacean characteristics, strongly attached auditory bullae, attached pelvis [3]. Rodhocetus: Cetacean characteristics, attached pelvis (probably) [4]. Peregocetus: Cetacean characteristics, attached pelvis [7]. Georgiacetus: Cetacean characteristics, detached pelvis [5]. John Nagy Lec 2.6: Evidence for Evolution 24/36 Fossils Examples Genetics Refs Synapomorphies Body plan Vestiges Timeline A more accurate view: Indohyus did not become Pakicetus, etc. Rather, ancestries back to common ancestors, as depicted by the chart. This phylogeny represents evolutionary relationships. Each connection is a node. Nodes represent ancestors. Therefore, at least 17 species are represented: the 9 named + 8 nodes. Groups are defined by synapomorphies (red). Example: Indohyus is more closely related to baleen whales (Mysticetes) that to hippos. John Nagy Lec 2.6: Evidence for Evolution 25/36 Fossils Examples Genetics Refs Mammals Avians Tetrapods These patterns are common: Mammals Fossils show transition of reptiles to mammals: Bottom: Early synapsids called pelycosaurs have reptile (laid eggs, jaw attached to back of skull), some mammal-like, characteristics. Middle: Later synapsids, called cynodonts, are more mammal-like (maybe hair, and milk) but retain some reptilian characteristics (laid eggs). Top: Even later synapsids become modern mammals (have hair and feed young with milk, jaw attachment underneath skull). John Nagy Lec 2.6: Evidence for Evolution 26/36 Fossils Examples Genetics Refs Mammals Avians Tetrapods Another transitional fossil This is a fossil dinosaur called Microraptor [8]. Long, bony tail and teeth, unlike birds. Feathers over its body, with long feathers for gliding on arms and legs. Chemical traces in the fossil suggest black, slightly irridescent feathers like modern black birds. John Nagy Lec 2.6: Evidence for Evolution 27/36 Fossils Examples Genetics Refs Mammals Avians Tetrapods These patterns are common: Birds Birds came from dinosaurs. Many dinosarus with feathers have been discovered, including Velociraptor of Jurassic Park and Jurassic World fame. Feathers are synapomorphic in one group of dinosaurs. All creatures defined by feathers, including birds, are nested within the dinosaur group; therefore, dinosaurs by definition never went extinct. Unrelated traits|patterns of bone articulations in the digits, for example|are synapomorphic in precisely the same group. John Nagy Lec 2.6: Evidence for Evolution 28/36 Fossils Examples Genetics Refs Mammals Avians Tetrapods These patterns are common: Tetrapods Tetrapods (4-legged creatures) came from fish Early lobe-finned fish (Eusthenopteron): bones in fin similar to tetrapod pattern before any vertebrates existed on land. Tiktaalik (middle) is a nearly perfect transition between fish and amphibians|it possesses key characteristics of both.
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