Download - Vertebrate Evolution Lecture 24
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Vertebrate Evolution
Lecture 24
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Chordates
• Chordates are members of the phylum Chordata– Their nearest animal relations are the echinoderms
• However, chordates employ a truly internal endoskeleton
• Chordates are quite diverse
Fig. 21.40
Tunicate
Lancelets
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• Distinguishing features of chordates
– 1. Notochord• A stiff, but flexible rod, that forms beneath the nerve cord
– 2. Nerve cord• A single dorsal nerve to which other nerves are attached
– 3. Pharyngeal slits• A series of slits behind the mouth into the pharynx
– 4. Postanal tail• A tail that extends beyond the anus
• All chordates have all four of these at some time in their life
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• With the exception of tunicates and lancelets, all chordates are vertebrates
• Distinguishing features of vertebrates– 1. Backbone
• A bony vertebral column replaces the notochord – 2. Head
• Well-differentiated, with skull and brain
• All vertebrates have an internal skeleton made of bone and cartilage against which the muscles work– This makes possible great size and movement
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• The first vertebrates evolved around 470 mya in the oceans
• Jawless fish – – Ostracoderms – toothless, scavangers– Agnathans
• Hagfish• Lampreys
• Cartilaginous skeleton• Invasion of the land
– First – fungi and plants (around 500 mya)– Second – arthropods (around 410 mya)– Third – vertebrates (360-280 mya)
• Amphibians were the first to live on land
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Fig. 20.08
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An evolutionary timeline
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Fish• Four characteristics
– 1. Gills• Used to extract dissolved oxygen gas from water
– 2. Vertebral column• An internal skeleton with a spine surrounding the dorsal
nerve cord– 3. Single-loop blood circulation
• Blood flow: Heart Gills Body Heart again– 4. Nutritional deficiencies
• Inability to synthesize the aromatic amino acids
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The Evolution of Jaws
• Jaws addressed two challenges faced by predators– 1. How to grab and hold prey– 2. How to pursue prey
• Jaws evolved from arch supports (about 410 mya)
Fig. 22.10
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• Fish Evolution• Early forms: Spiny fishes and placoderms • Sharks: light skeleton – cartilage
– Class Chondrichthyes• Skates and rays are flattened sharks that
are bottom-dwellers• advanced reproduction system – internal
fertilization•
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Class: Osteichthyes - Bony Fish
• Stiff internal skeletons – firm support for muscle action
• Swim bladder – creates neutral buoyancy• Gil cover - Operculum – allows fish to
pump gills to circulate water while motionless
• Lateral line system – sensory – detects changes in pressure, predators near by, presence of prey
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Fig. 20.11
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• Amphibians are direct descendants of fishes
• They are the first vertebrate to walk on land
• They include – Frogs– Toads– Salamanders– Caecilians
22.5 Amphibians Invade the Land
Fig. 22.14 Red-eyed tree frog
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Amphibians• Carnivores• Developed from lobe finned fish• Leg development required skeletal
modification• Terrestrial adaptation – means to acquire
oxygen:– Cutaneous respiration – moist skin– Lung development – internal moist surface– Pulmonary circulation– 3 chambered heart – oxygenated blood
separated from deoxygenated blood
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Characteristics of Amphibians
• 1. Legs: prob. development from lobe finned fish
Fig. 22.15 Evolution of legs
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Characteristics of Amphibians
• 2. Lungs– Provide a more efficient means of respiration than gills
• 3. Cutaneous respiration– Respiration directly across the skin supplements the use
of lungs• 4. Pulmonary veins
– Two large veins that return aerated blood to the heart for repumping
• 5. Partially divided heart– Separates the blood circulation into two separate paths
• Pulmonary and systemic
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• The heart beat in fishes has a peristaltic sequence– Starts at the rear (SV) and moves to the front
• Gill respiration provides fully oxygenated blood to the body
– However, circulation is sluggish• This limits rate of
oxygen delivery to rest of body
Fig. 25.13b
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Amphibian and ReptileCirculation
• The advent of lungs resulted in two circulations
– 1. Pulmonary circulation• Delivers blood to the lungs
– 2. Systemic circulation• Delivers blood to the rest of the body
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• The amphibian heart has two structural features that reduce mixing of oxygenated & deoxygenated blood
– 1. The atrium is divided into two chambers by a septum
– 2. Conus arteriosus is partially separated by another septum
• Amphibians in water supplement the oxygenation of blood by a process called cutaneous respiration
Fig. 25.14a
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Fig. 20.14
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Amphibian Reproduction• Dependent on water environment• Eggs laid in water• External fertilization in watery environment• Young develop in water• Some unique adaptations enable
colonization of dry habitats– Example: young develop in mouth of adult
• Adults become terrestrial
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Reptiles
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ReptilesImproved Adaptation to Terrestrial Live
• Dry Skin – prevention of desiccation• Thoracic breathing – Efficient system of
drawing air in and out of lungs • Improved cardio-vascular• Improved leg attachments – rapid
movement
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• Among reptiles, additional modifications have further reduced the mixing of blood in the heart
– The ventricle is partially divided into two chambers by a septum
–They thus have completely divided pulmonary and systemic circulation
• The separation is complete in the crocodiles
Fig. 25.14b
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Fig. 20.04b
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Fig. 20.03
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Fig. 20.04a
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Reptile – Reproduction• Eggs laid on and develop on land – even
by aquatic species
– Internal fertilization– Egg developed as self contained
survival/developmental structure
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Amniotic egg • Watertight - four membranes
– Chorion: Allows O2 entry– Amnion: Fluid-filled cavity– Yolk sac: Provides food– Allantois: Excretes waste
Fig. 22.17
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Birds – Class AvesReptile Adapted for Flight
• Scales on leg – evidence for reptilian ancestry• Temperature regulation• Feathers – Did they arise for flight or insulation?• Improvements to oxygen gathering/circulation
– Four chambered heart• Flight improvements
– Skeletal modifications• Wing bones• Keel• Light weight
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Fig. 20.16
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http://www.nature.com/nature/journal/v420/n6913/fig_tab/nature01196_F5.html
http://home13.inet.tele.dk/palm/origbird.htm
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Fig. 20.05
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Fig. 20.17
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Mammals• Major characteristics:
– Mammary Glands – modified sweat glands– Hair – Keratin filled cells– Middle ear structure
• Other characteristics:– Extended care for young– Behavioral flexibility – reflection of brain
development– Dentition – heterodent – 4 types of teeth– Highly developed for life on land – some
returned to water
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Fig. 20.19
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• Mammals – Major Groups• Prototherians
– Shelled eggs– Few living examples: duck billed platypus
Monotremes• Therians
– Viviparous – young born alive– Includes:
• Marsupials – young born early, develop in pouch• Examples: kangaroo, opossum• Placental – development in placenta within uterus• Example: us (humans)
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Fig. 22.22
Other Characteristics of Modern Mammals
• Placenta
– Brings the bloodstream of mother and fetus into close contact• The two don’t mix
– Characteristic of most mammals
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Mammal Diversity• Empty niches became available with extinction
of dinosaurs• Radial evolution to fill niches occurred – great
diversity developed
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• Evolution of Whales – A Story– Mammal returns to the water– Gradual evolution of characteristics important
to survival in water– Loss of limbs (vestigial structures remain)– Increase in size – in some– Migration of nasal openings to top of head– Other physiological developments for deep
diving– Toothed and baleen whales develop
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http://www.dolphinquest.org/learningquest/dolphinfacts/dolphins/info5.htm
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http://edwardtbabinski.us/whales/whale-tail.html
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Evolution of Primates – Another Story
• Group includes:– Prosimians– Tarsioids– Anthropoids
• Monkeys• Apes• Hominoids – including us
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History of Mammals
• Over 4,500 species of mammals exist today– Almost one-quarter are bats!
• There are only 233 known species of primates
• Humans evolved less than 2 mya– There have been at least three species
• Only Homo sapiens is alive today!
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Mammals• Extended care for young – mammary
glands• Increased brain development• Endothermy• Radial evolution – adaptations to many
habitats and niches
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Primates• Tree dwelling (arboreal)• Nocturnal• Insectivorous (early forms)• Grasping fingers and toes – opposable thumb• Binocular vision – judge distance• Nails (as opposed to claws)• Well developed brain• Single birth• Extended care of child by parent
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Early split in primate evolution1. Prosimians
– Tarsiers– Lemurs
2. Anthropoids – ‘Higher Primates’– New World monkeys– Old world monkeys
• Apes• homonids
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• Prosiminans
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Anthropoids – ‘Higher Primates’– Color vision– Expanded brain capacity– Improved senses– Care of young– Social interactions
• Prolonged learning• Brain development
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Hominid evolutionary considerations–Bipedalism–Brain case size (evidence of cerebral
development)–Dentition – teeth- (evidence of type of diet)–Tool use–Evidence of cultural development (art, religion,
etc.)–Did Humans evolve in Africa or did they evolve
in a number of locations?• Out of Africa migrations possibly two migrations?
– vs.
• Multiregional evolution
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• The common ancestor of apes and hominids is thought to have been an arboreal climber
– Hominids became bipedal (walking upright)
– Apes evolved knuckle-walking
• Anatomical differences between the two are related to bipedal locomotion
Comparing Apes to Hominids
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Comparing Apes to Hominids
Fig. 23.5
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Early Hominid Forms• Australopithecus spp. – ‘southern ape’
– 7 recognized species – Hadar region Ethiopia (Africa)– Upright /bipedal locomotion– Increase in brain size– Sexual dimorphism – different size/appearance– Australopithecus afarensis –’Lucy’
• 3.2 million years old
• http://www.becominghuman.org/
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Homo habilis
• ‘handy man’ - for tool use• ~ 2.5 million years ago• Remains from various locations in Africa• Other hominid forms present during those
times• Possible development of speech -
development of Broca’s area?
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Homo erectus• ‘upright man’• ~ 1.8 million years ago until 2-300,000
years ago• Tall and big, increase in brain size
– Brain size close to that of modern humans • Less sexual dimorphism• Eastern Africa• Probably migrated out of Africa• Remains from Africa, India, China,
Indonesia, Europe
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Fig. 23.12 Our own genus
H. habilis
H. neanderthalensis
H. erectus
H. sapiens (Cro-Magnon)
Essentially the same as human
skulls today
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The Last Stage ofHominid Evolution
• Modern humans first appeared in Africa about 600,000 years ago
– Three human species are thought to have evolved• Homo heidelbergensis• Homo neanderthalensis• Homo sapiens
The sole surviving hominid
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The Last Stage ofHominid Evolution
• Homo heidelbergensis– Evolved in Africa about 600,000 years ago– Migrated to Europe and Western Asia
• Homo neanderthalensis– Appeared in Europe about 130,000 years ago
• As H. heidelbergensis was becoming rarer– Likely branched off of the ancestral line leading to
modern humans
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Out of Africa Hypothesis• fossils of modern-like humans are found in
Africa • stone tools and other artifacts support
African origin • DNA studies suggest a founding population
in Africa
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Fig. 23.13 Out of Africa – many times
H. erectus
H. heidelbergensis
H. sapiens
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H. erectus (or H. heiderbergensus) to H. sapiens
• Two possible branches– H. sapiens – early form: Cro-Magnon– H. neanderthalensis
• H. sapiens evolved in Africa• H. neanderthalensis in Europe• H. erectus similar to modern man
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H. sapiens and H. neranderthalensis• Two quite different species
–Different anatomical features–Probably diverged from a common ancestor but
quite some time prior to meeting in Europe and the middle east – possibly after a second out of Africa migration
–Evidently socially and intellectually quite advanced• Evidence of religion• Diverse tool technology
–No evidence for interbreeding with H. sapiens
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23.9 Our Own Species:Homo sapiens
• Neanderthals (H. neanderthalensis) – Named after the Neander Valley of Germany where their
fossils were first discovered in 1856– Evolved in Europe, then migrated to Asia– Abruptly disappeared about 34,000 years ago
• Cro-Magnons (H. sapiens) – Named after the Valley in France where their fossils were
first discovered– Evolved in Africa, then migrated to Asia– Eventually spread to N. America and Australia
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