CHAPTER 34 – Vertebrates
- VERTEBRATES – Animals which possess a backbone (vertebral column); Evolution of vertebrates began about 540 million years ago
Concept 34.1 – Chordates Have a Notochord and a Dorsal, Hollow Nerve Cord
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Vertebrates are a subphylum of the phylum CHORDATA; CHORDATE – Bilaterally symmetrical animals within Bilateria
Characteristic
Notochord
Dorsal, hollow nerve cord
Pharyngeal clefts and slits
Muscular post anal tail
Structure and Function
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Longitudinal, flexible rod that provides skeletal support against which muscles work during swimming
Unique to chordates; Develops from plate of ectoderm that evolves into central nervous system = brain + spinal cord
Series of pouches separated by grooves which develop into slits that open to the outside of the body
Function as suspension-feeding devices; Vertebrates  Develop into gills or ears and other head or neck structures
Tail extending posterior to anus that propels force in many aquatic species
Tunicates
 Belong to deepest branching lineage of chordates
 LARVAE  Use tail muscles and notochord to search for
suitable substrate, then undergoes metamorphosis
 ADULT  Draws in water and filters food particles by
mucous net; Also shoots jets of water: “sea squirts”
Lancelets
 Gets name from bladelike shape  Also undergoes
metamorphosis; uses suspension feeding in water
column with side-to-side undulations
 Small clusters of the Hox gene express themselves in
lancelet’s nerve cord, similar to vertebrate brain
Concept 34.2 – Craniates are Chordates that Have a Head
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Brain, eyes and other sensory organs lead to a new way of feeding called active predation
Transitioned from chordates during Cambrian explosion 530 million years ago; Most primitive was the Haikouelle: lacked a skull
Characteristic
Duplicated genes
Neural crest
Gill slits
Extensive muscular system
Structure and Function
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Two clusters of Hox genes and other duplicated genes add to genetic complexity for more complex morphologies
Collection of cells that give rise to teeth, bones, cartilage of skull, facial skin, neurons and sensory capsules
Allow water to be pumped through slits for sucking in food; Also facilitate gas exchange
Heart with at least two chambers, red blood cells and haemoglobin Increase metabolism + kidneys remove waste
Hagfishes
 Least derived of craniate lineage  Has a skull of cartilage and swims in snakelike fashion by exerting force against notochord
Concept 34.3 – Vertebrates are Craniates that have a Backbone
Characteristic
Vertebrae
Extensive skull
Fins for aquatic
Structure and Function
 Encloses the spinal chord and takes the mechanical roles of notochord; simply cartilage pieces for some vertebrates
 Duplication of transcription factor genes further develop nervous system
 Acquire dorsal, ventral and anal fins for thrust and steering control, supported by an efficient gas exchange system
Lampreys
 Oldest living lineage of vertebrates; parasites that feed by clamping jawless mouths onto fish, piercing the skin to ingest blood
 Have a skeleton of cartilage with no collagen and a notochord as a main axial skeleton; cartilaginous projections extending
dorsally partly enclose the nerve cord
Fossils of Early Vertebrates and Origins of Bone and Teeth
 Early vertebrates were jawless, such as conodonts; Possessed mineralized dental tissues and elements called cone teeth
 Ordovician, Silurian and Devonian fossils: Paired fins and inner ear = balance; armoured with mineralized bone (ostracoderms)
 Mineralization began in the mouth to accommodate larger prey  Manifested into armour and endoskeleton
Concept 34.4 – Gnathostomes are Vertebrates that have Jaws
Characteristic
Jaws
Enhanced sensory systems
Endoskeleton
Paired appendages
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Structure and Function
 Hinged structure helps grip food items and slice them up
 Duplication of genes furthered embryo complexity to enhance smell and vision and introduce of lateral line system
(organs become sensitive to vibrations in surrounding water)
 Supports axial skeleton and shoulder girdle
 Allow balance
Gnathostomes diversified 470 million years ago during Ordovician period due to:
o a. efficient swimming by paired fins and tail
b. Jaws that easily grab and bite prey
Earliest gnathostomes: placoderm (“plate-skinned)  Other group of jawed vertebrates: acanthodians
Chondricthyans (Sharks, Rays and Relatives)
 Fish with skeletons composed of cartilage  Mineralization and traces of bone are derived conditions
 SHARKS have streamlined, powerful bodies with stabilizing dorsal fins; mostly carnivorous, but largest are suspension feeders
o OVIPAROUS – Lay eggs encased in protective coats that hatch outside the mother’s body
o OVOVIPAROUS – Retain fertilized egg in oviduct, with eggs hatching and developing in uterus
o VIVIPAROUS – Young develop in uterus and obtain nourishment by receiving nutrients from mother’s blood
 RAYS are similar to sharks but are flattened bottom-dwellers that use jaws to crush molluscs and crustaceans
o Use pectoral fins to propel through water and is provided protection by whip like tail and venomous barbs
Ray-Finned Fishes and Lobe-Fins
 Osteichthyes – Clade which contains vast majority of vertebrates; members have ossified endoskeletons of calcium phosphate
 Fish: Breathe by drawing water over gills; have bony scales covering skin and glands that secrete mucus to reduce drag during
swimming; posses a swim bladder controlling buoyancy (preceded by lungs); reproduce oviparously
1. Ray finned fishes (e.g. bass, trout, perch) are supported by flexible rays for manoeuvring and defence
2. Lobe fins (Sarcopterygii) have rod shaped bones surrounded by muscles; only three lineages survive
 Coelacanth – Once believed to be extinct; a second population has been identified near Indonesia
 Lungfishes – Three genera found in fresh water which surface to gulp but also has gills
 Tetrapods – Clade that contains vertebrates with limbs and feet developed during Devonian period
Concept 34.5 – Tetrapods are Gnathostomes that have Limbs and Feet
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360 million years ago, fins of some lobe-fins evolved into limbs and feet of tetrapods, taking many new forms
Characteristic
Four limbs
Ears
Pectoral limbs
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Structure and Function
 Support weight on land and feet with digits that transmit muscle generated forces
 Pharyngeal clefts became ears, glands and other structures; ears adapted to the detection of airborne sounds
 Birds gained wings while whales gained fishlike shape
Developed by a modification of a pre-existing body plan  limbs already moved across land and logs while lungs breathed in
areas of oxygen-poor water; Diversity arose during Devonian and Carboniferous periods
Amphibians
 Contains about 4800 species in which most have moist skin for respiration
1. Urodele – “The tailed ones” which walk side to side by bending of body; primarily salamanders
2. Anurans – “The tail-less ones” which move on land with hopping hind legs; primarily frogs and toads
3. Apodans – “The legless,” also the caecilians, that resemble earthworms and inhabit tropical areas
 Experience metamorphosis  E.g. the frog begins as an aquatic herbivorous tadpole with gills, until it develops legs, lungs and a
carnivorous digestive system, loses its gills and lateral line system to become a terrestrial hunter
 Must have moist environment or high humidity for gas exchange; external fertilization must be in moist area
Concept 34.6– Amniotes are tetrapods that have a Terrestrially Adapted Egg
Characteristic
Amniotic egg
Less permeable skin
Ability to use rib cage
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Structure and Function
 Extraembryonic membranes form tissue layers for gas exchange, waste storage and transfer of stored nutrients to
embryo; named for amnion membrane  Most amniotic eggs have shell, slowing dehydration, occupying wider area
 Develop use of lungs as opposed to gas exchange with environment through skin
 Further develop use of lungs by ventilating the lungs
Developed by a modification of a pre-existing body plan  limbs already moved across land and logs while lungs breathed in
areas of oxygen-poor water; Diversity arose during Devonian and Carboniferous periods
Reptiles
 Have scales that contain keratin, a waterproof barrier preventing dehydration  Rely on lungs to breathe  Mostly oviparous
 Cold-blooded: Use behavioural adaptations to control body temperature as opposed to metabolism (e.g. seek sun)
 ECTOTHERMIC – Explains absorption of external heat as main source of body heat; ENDOTHERMIC is metabolic based
 Parareptiles – First group of reptile to emerge, evolving into turtles
 Diapsids – Diversifying clade with holes on each side of the skull behind the eye socket; separated into:
1. Archosaurs – Including crocodilians, pterosaurs and dinosaurs
1. Pterosaurs – First tetrapods to take to the air with wings and dynamically adjusted membranes
2. Dinosaurs – Had behavioural adaptations for warm climate; extinct by Cretaceous period
 Ornithischian branch was made of herbivores with elaborate defenses while theropods were bipedal
carnivores (eg. Tyrannosaurus rex) and ancestors of birds
3. Crocodilians – Belong to an archosaur lineage that reaches back to the late Triassic period  Originally small
terrestrial quadrupeds with long, slender legs  Became larger and adapted to aquatic environments
2. Lepidosaurs – Represented by two species of lizard-like reptiles
 Tuataras – Appeared 220 million years ago, but now found only off of New Zealand
 Squamates – Including lizards and snakes  Lizards are the most numerous reptiles
 Snakes are carnivorous with adaptations for hunting and eating prey (e.g. sensors and poison)
3. Turtles – Most distinctive group with boxlike shells made of upper and lower shields fused to the vertebrae, clavicles and ribs
 Earliest turtles evolved into pleurodires (turtles that horizontally fold the neck) and cryptodires (fold vertically)
Birds
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Considered part of the archosaurs with adaptations to flight  Lighter weight: absence of urinary bladder and teeth, one ovary,
smaller gonads and a lighter skull  Feathers made of b-keratin  Flapping power comes from pectoral contractions
Flight enhances hunting and scavenging  Consume insects in air and escape predators
Active metabolism needed: Maintain body temperature by insulation and efficient respiratory system
Originated from theropods 150 million years ago  Feathers initially used for insulation, camouflage and courtship
o Ratites – Nonflight species including the ostrich, rhea, kiwi and emu
o Spenisciformeds – Order consisting of penguins, who use pectoral muscles for swimming
Concept 34.7– Mammals are Amniotes that have Hair and Produce Milk
Characteristic
Mammary Glands
Hair
Diaphragm
Teeth differentiation
Larger brain
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Structure and Function
 Produce nourishing milk rich in fats, sugars, proteins and vitamins for offspring
 When coupled with fat layer underneath skin, helps to retain heat; support metabolism with efficient respiratory and
circulatory systems
 Flap of skin which helps ventilate lungs
 Help adapt for chewing many kinds of food (eg. molars and premolars)
 More capable learners  Parental care is also extended for offspring to learn important survival skills
Once belonged to group called synapsids which lacked hair and laid eggs  First true mammals arose during Jurassic period;
Had small sizes possibly because dinosaurs occupied ecological niche of large-bodied animals
Monotremes – Egg laying mammals consisting of only three species; Have hair and produces milk, but posses no nipples
Marsupials – Mammals in which embryo develops inside the uterus of the female’s reproductive tract and offspring are born
very early in development; nursed in maternal pouch called the marsupium
o Indicates biological + geological evolution: diversification and convergent evolution on different continents
Eutherians – Mammals with more complex placentas; longer periods of pregnancy; embryo develops completely within uterus
Primates
Characteristic
Structure and Function
Hands and Feet
Large brain
Unique face
Thumbs and toes
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Adapted for grasping, specifically for tree branches; skin ridges become human fingerprints
May explain relatively well-developed paternal care and complex social behaviour
Short jaws, flat face and forward looking eyes; visual fields overlap to enhance depth perception
Appendages used for power grips for tree-dwelling; *excellent eye-hand coordination
Living primates includes three main groups: 1. Lemurs, lorises and pottos
2. Tarsiers
3. Anthropoids
o First monkeys (anthropoids) evolved in the Africa and Asia, spreading to the New World during Ogliocene  Two
populations of monkeys underwent separate adaptive radiation after millions of years of separation
o Hominoids – Other group of anthropoids consisting of primates (apes)  Diverged 25 million years ago
 Relatively long arms, short legs and no tail; all nonhuman hominoids spend time in trees; hominoids have
larger brain in proportion to body size; varying social organization
Concept 34.8– Humans are Bipedal Hominoids with a Large Brain
Characteristic
Bipedal
Larger brain
Shorter jaw
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Structure and Function
 Walk upright on two legs
 Allows for language, symbolic thought and the manufacture and use of complex tools
 Reduced jawbones and jaw muscles, accompanying a shorter digestive tract
PALEOANTHROPOLOGY – Study of human origins  20 species of extinct hominoids close to humans discovered
o Oldest S. tchadensis (7-6 million years ago) share reduced canine teeth, bipedalism and foramen magnum
o Brains of early hominoids were significantly small in volume and bodies were much smaller
 MOSAIC EVOLUTION – Differing rates of evolution
Australopiths
 Hominid diversity increased dramatically 4-2 million years ago  Collectively called Australopiths
 Named for Australopithecus africanus who walked fully erect and had human-like hands and teeth, though 1/3 size of brain 
Also found “Lucy,” 3.24 million year old Australopithecus skeleton = A. afarensis
o A. afarensis had longer lower jaw, smaller brain, long arms, but demonstrated bipedalism
Significant Trends
 BIPEDALISM  Theory: A drier climate and increased savanna area prevented tree-dwelling hominids from moving through
canopy, forcing bipedalism  But did not become bipedal in simple linear fashion
o 1.89 million years ago: More arid climate meant less energy walking on two legs = long distances walked
 TOOL USE  Manufacture and use of complex tool is a derived behavioural character of humans  Hominids cut flesh from
bones of animals using stone tools
o Fossils indicate that stone tool use originated before evolution of large hominid brains
Early Homo
 Homo habilis: Earliest fossils in Homo group (2.4-1.6 million)  Shorter jaw, larger brain volume, sharp tools
 Homo ergaster: (1.9 million) Substantially larger brain, long, slender legs with hip joints for walking, short fingers
o Smaller teeth indicated a change in diet and food preparation  Cooked or mashed the food, mostly meat
o Sexual dimorphism reduced  Males and females engaged in more pair-bonding than earlier hominids
 Led to long-term biparental care of offspring  Depend on parents for food and protection
o Early member of species Homo erectus: first hominid to migrate out of Africa (1.8 million)
Neanderthals
 40 000 fossil belonged to thick-boned, heavy hominid with prominent brow (Homo neanderthalensis)  Appeared in Europe
and Near East 200 000 years ago  Large brain, capable of making hunting tools from stone and wood
 DNA evidence: All Neanderthals form a clade while modern day humans more related to different races
Homo sapiens
 Oldest known fossils of own species found in Ethiopia; DNA suggests that all living humans had ancestors in Africa  Spread
first to Asia then to Europe and Australia, arriving in the New World 15 000 years ago
 Homo floresiensis also found in Indonesia: Much shorter, smaller brain volume but the skull thickness and proportions of teeth
and shape indicate that it descended from Homo erectus
 Homo sapiens survived with creativity, symbolic thought and languages  Raised survival and reproductive fitness
o Supported by FOXP2 gene identified for human language
- Biological diversity is the product of branching phylogeny not ladder-like progress