Chapter 34: Origin & Evolution of Vertebrates
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What's an important note about phylum vertebrata?
Not all species in phylum vertebrata are vertebrates!
- Deuterostomes including:
True or false: All Chordates have an internal skeleton
False! Not all chordates have an internal skeleton, although they all did at some point of development.
Four main features of Vertebrates (at some point of development).
- 1. Dorsal, hollow nerve cord (differentiates into brain and nerve cord)
- 2. Notocord
- 3. Pharyngeal gill slits or pouches
- 4. Post-anal tail
What happens to the dorsal, hollow nerve cord in chordate development?
It differentiates into brain and nerve cord
In Chordates, the notocord becomes ?
The vertebral column aka backbone
What are pharyngeal gill slits or pouches used for in non-tetrapods?
How about in Tetrapods?
- used for gas exchange in non-tetrapods
- become parts of ear and other head and neck structures in tetrapods
True of false: All known chordates have the same 4 basic characteristics.
- False. All four of these features are present in chordates at some point in their development.
- Some of these features are lost in the adult organism.
How are chordate muscles arranged?
Into segmented blocks
Do all chodates have a skeleton?
No. Not all, but most do
The Non-vertebrate chordates:
Two of three sub-phyla of chordates are non-vertebrate
1. Urochordata = tunicates and salps
2. Cephalochordata = lancelets
How many of the sub-phyla of Chordates are non-vertebrates?
What are the two sub-phylums of Chordates that are not vertebrates?
- Urochordata: Tunicates and salps
- Cephalochordata: Lancelets
Characteristics of Subphylum Urochordata:
- Tunicate and salps are marine animals
- Immobile as adults
- Only larve have notochord and nerve chordAdults have cilia lined pharynx that brings in water where small food particles are then trapped in a sheet of mucus.
- Adult tunicates may be colonial
- tadpole-like larve do not feed and are free-swimming for only a few days before attaching to substrate by means of a sucker
- Tunic surrounds and supports animal
- One group of tunicates (Larvacea) retain their tail and notochord into adulthood; possibly, vertebrates evolved from a larval form that became able to reproduce.
In subphylum urochordata, only ____ have a notochord and nerve chord.
Adult tunicates and salps feed on small food particles trapped in a sheet of mucus. Where is this mucus secreted from?
Secreted from the endostyle
Adult tunnicates may be ____.
This tunnicate retains it's tail and notochord into adulthood. Why is this significant?
- Vertebrates may have evolved from a larval form that became able to reproduce
Characteristics of subphylum cephalochordata
- Lancelets look like a two edged surgical knife
- Former genus is Amphioxus, but now known as genus Branchiostoma
- Notochord retained throughout life
- Spend most time partly buried in sand with anterior end exposed
- can swim, but don't often
- more pharyngeal gill slits than fishes
Which of the non-vertebrate chordate subphyla retains a notochord throughout life and which has a notochord only as a larvae?
- Subphylum Cephalochordata retains the notochord throughout life
- Subphylum Urochordata only have a notochord during larval stage (except fpr the Larvacea)
____ look like a two-edged surgical knife
Subphylum Cephalochordata in known as genus _______. Formally known as _____.
Chordates with spinal column
Vertibrates differ from tunicates and lancelets in two important respects:
- 1. Vertebral column
- 2. Distinct and well-differentiated head (craniates)
What are some other important differences between vertbrates and tunicates and lancelets?
- Vertbates have a neural crest
- Internal organs (liver, kidneys, endocrine-glands, heart and closed cirulatory system, excretory system)
What advantage does bone have over chitin?
Bone is living tissue that is strong without being brittle like chitin
Overview of Vertebrate evolution:
- Vertebrates evolved from oceans about 545 million years ago
- Hinged jaw was major advance for food gathering, jawed fish dominate the sea
- Amphibians invaded land
- Amphibians gave rise to reptiles 300mya
- Within 50 million years, reptiles living on land replaced the amphibians as dominant land vertebrates
- Reptiles gave birth to birds and mammals
- Dinosaurs and mammals appear at about the same time in fossile record
- Dinosaurs dominated and the largest mammal was about the size of a small dog!
- Dinosaurs disappeared about 65 mya in Cretaceous period, opening door for mammals and birds to diversify and flourish
____ was a major advancement in food gathering
What percentage of vertebrates are fishes?
More than half!
Five key characteristics of fishes:
- Vertebral column
- Jaws and paired appendages
- Internal gills for extracting dissolved oxygen from water
- Single-loop blood circulation
- Nutritional deficiencies
Vertebral column in fishes:
- Bony or cartilaginous spine surrounding dorsal nerve cord and bony or cartilaginous skull encasing brain
- Exceptions are jawless hagfish and lampreys
Jaws and paired appendages in fishes:
- Most fished have a pair of pectoral fins and a pair of pelvic fins, fins are jointed in lobe-finned fish
- Except jawless hagfish and lamreys
Internal gills in fishes:
Extract dissolved oxygen from water
Single loop blood circulation:
- Pathway is from heart>gills>body tissues>back to heart
- Heart is 2 chambered
Fishes must obtain the amino acids phenylalanine, tryptophan, and tryosine from their diet as the cannot synthesize these on their own
The first fishes:
- Jawless, only had mouth positioned anteriorly that could open to take in food (modern day example: jawless hagfish and lampreys)
- Ostracoderms now extinct, but had bony head and cartilaginous skeleton
How did the jaw evolve?
- Evolved from most anterior gill arches
- Teeth evolved from modified scales on skin that lined the mouth
The jaw evolved from ___ and teeth evolved from ____.
- jaw- from gills
- teeth- from scales
How did sharks become the top predators of the sea?
- Structure of jaw much improved so that a shark could open mouth much wider
- Excellent swimmers and aggressive predators
____ were among the first to develop teeth.
True or false: Teeth are set in the jawbone
False. Not set in the jawbone, but instead they sit on top of it.
Sharks may have as many as __ rows of teeth. When a tooth is lost, what happens?
- Up to 20 rows of teeth!
- When a tooth is lost, the tooth behind it moves forward to replace it
The lateral line system:
- Series of sensory organs projecting into a canal tat runs the length of a fishes body
- Open to exterior through series of sunken pits
The lateral line on a fish is equivalent to what?
Sharks have (internal/external) fertilization.
- Sharks have internal fertilization
- Shark pups are born alive
What has lead to the population decline of sharks?
- Long gestation period and relatively few offspring
- Sharks are captured in Asian countries (shark fin soup, etc)
How did bony fish come to dominate the water?
- Heavy internal skeleton of bone provides strong base against which strong muscles can pull
- Mobile fins, thin scales, symmetrical tails
- Bony fish are the most species-rich group of all vertibrates
Outpocketing of pharynx; can be filled with gas or drained of gas to control buoyancy in water
Gill cover, aka ?
- pumps water over gills
- Works like a bellows
- This flow of water over the gills allows fish to remain stationary
What are the two groups of bony fish?
Parallel bony rays support fin; no muscles within the fin
- Fins are fleshy and muscular
- Supported by bone with articulated joints
- muscles within fins can move fins independently of one another
- No ray-finned fish can do this
- Only 8 species of lobe-finned fish exist today
- Amphibians evolved from lobe-finned fish
The evolutionary pathway to land ran through the ______ fishes
Name two of the 8 species of lobe-finned fish still in existence:
Frogs, salamanders, and caecilians are direst descendants of ____.
- They are the first vertebrates to walk on land
What are the three orders of Amphibians?
- Order Anura ("without a tail")
- Order Urodela ("visible tail")
- Order Apoda ("without legs")
Order Anura (of the amphibians)
- "without a tail"
- frogs and toads
- live in deserts, mountains, ponds
- return to water for reproduction
- moist skin
- broad body
- long hind legs
- live in or near water
- tadpole-->adult frog
Do all frogs come from tadpoles?
No. Frogletts hatch in some tropical species that don't live near water
Order Urodela (of the amphibians)
- "visible tail"
- newts and salamanders
- elongated bodies, long tails, smooth moist skin
- love in moist habitats, some in water
- internal fertilization where female picks up sperm packets left by male
- eggs laid in moist areas or water
Larval salamanders are similar to adults except ?
- they live in water and have external gills
- gill slits that disappear during metamorphosis
Order Apoda (of the amphibians)
- "without legs"
- Legless, worm-like tropical burrowing amphibians
- small eyes and are often blind
- size from 30 cm to 1.3 m long
- have jaws with teeth and eat worms and other invertebrates
- Internal fertilization
Five distinguishing features of amphibians
- 1. Legs
- 2. Lungs
- 3. Cutaneous respiration
- 4. Pulmonary veins
- 5. Partially divided heart
frogs and salamanders have four legs, caecilians have lost their legs
Cutaneous respiration in amphibians:
- a lot of surface area of moist skin allows for diffusion or oxygen through skin which must be kept moist
- supplements use of lungs
Return aerated blood to heart for repumping
Partially divided hear in amphibians:
- Imperfect separation of pulmonary and systemic blood circulation
- only one ventricle in heart where oxygenated and deoxygenated blood mix.
The development of ___ helped to support animals on land.
Legs. Amphibian ancestors had rather large bodies and it may have been difficult to support weight of body on land
What happens to gills when the come in contact with the air? What was the solution to this problem?
- They stick together
- Lungs were developed
Why was the heart and circulatory system modified in amphibians?
For more efficient delivery of oxygen to muscles
Amphibians still reproduce in water, why?
So their eggs won't dry out
The first amphibians were thought to have shown up in what is now called ____.
- Greenland was a part of north america at the time and the earliest amphibian fossils are found in north america
earliest amphibian fossils
What was discovered in Ichthyostega?
- Shoulder bones not attached to skull
- flipper shaped hind legs
- Broad ribs overlapped to make solid rib cage for lugs and heart
What is the likely reason why the floor of the mouth in amphibians lowers to push air down the windpipe?
Because broad ribs formed a solid rib cage that could not expand and contract for breathing
During the Permian perios, some amphibians left marshes to drier upland areas. These had bony plates covering their large bodies and leathery skin (to prevent water loss). Lungs were the only means of respiration.
Reptiles evolved from ____. One group of reptiles, the ______. came to dominate the land and the amphibians retreated back to the water.
How did reptiles improve upon the innovations of the amphibians?
- 1. leg arrangement supports body better allowing animal to be bigger and to run
- 2. more efficient heart and lungs
- 3. skin covered with scales to decrease water loss
- 4. Watertight covering evolved for eggs
Reptiles exhibit three key characteristics:
- 1. Amniotic eggs
- 2. Dry skin
- 3. Thoracic breating
- watertight eggs that contain a food source (yolk) and a series of four membranes.
- All modern reptiles, birds, and mammals show this pattern of membranes in the eggs.
4 parts of amniotic eggs (CAYA):
- Yolk Sac
- Outermost membrane lies just beneath the porous shell
- Allows for exchange of respiratory gases, retains water
Encases developing embryo within fluid-filled cavity
Provides food from yolk via blood vessels connecting to embryo's gut
Surrounds cavity into which waste products from embryo are excreted
Explain the dry skin of reptiles
- Layers of scales cover the body to prevent water loss
- Scales contain keratin, the same protein that forms claws, fingernails, hair, and bird feathers
____ is the protein that forms scales, flaws, fingernails, hair, and bird feathers.
Reptiles developed _____ breathing.
- Thoracic breathing
- The rib cage expands and contracts to suck air into lungs then force it out
The capacity of thoracic breathing is limited by what?
Limited by the volume of the lungs
Synapsids gave rise to ______ that became the mammalian line.
____ gave rise to modern reptiles and birds.
What are the 4 important characteristics of modern reptiles?
- Internal fertilization
- Mixing of oxygenated and deoxygenated blood is lessened by extending septum partially through ventricles
- Crocodiles, birds, and mammals have a four-chambered heart
- Ectothermic= obtain their heat from external sources (endothermic animals generate heat internally)
What are the 4 modern reptile groups? (CRSC)
- Order Chelonia
- Order Rhynchocephalia
- Order Squamata
- Order Crocodylia
Order Chelonia: contains what animals?
- Turtles and tortoises
- No teeth, but have a sharp beak
- Only reptiles to have a shell
- Only found on small islands off coast of New Zealand
- Have "third eye" on top of head, eye is covered by thin layer of scales; has lens and retina; connected by nerves to brain; may alert tuatara when it has been exposed to too much sunlight.
- Lizards and snakes
- Lack of limbs, movable eyelids, and external ears
- distinguished by paired copulatory organs in males
- head and jaws have strength and mobility
- most lizards and snakes are carnivorous.
- Crocodiles and alligators
- All crocodillians are carnivores
- Crocodiles resemble birds more than they resemble other reptiles
- Build nests, care for their young
- Have a four chambered heart
The success of birds has a lot to do with the development of what?
The development of the feather
Class ____ is the most diverse of all terrestrial vertebrates.
Class Aves (Birds)
Feathers in Birds:
- Modified reptilian scales made of keratin
- Provide lift for flight
- Conserves body heat
Flight skeleton of birds:
- Bones are thin and hollow
- Many bones are fused and make bird skeleton more rigid than reptilian skeleton
- No other living vertebrates have fused collarbone or keeled breastbone
- Fossil of first known bird
- Fossile found in Bavaria in 1862
- Had skull with teeth, very few fused bone
- Bones were probably solid and not hollow, had long reptilian tail, no enlarged breastbone, had feathers on wings and tail.
Name 3 evolutionary features from birds:
- Hollow Bones
- Super efficient lungs that permit sustained powered flight
Shared characteristics of Modern birds:
- 1. Efficient respiration
- 2. Efficient circulation
- 3. Endothermic
Efficient respiration in birds
Inhale-->air goes past lungs to air sacs near and within hollow bones of back --> air travels back to lungs --> anterior air sacs before exhaling
Efficient circulation in birds
- Four chambered heart-no mixing of oxygenated blood with deoxygenated blood
- Birds have rapid heartbeats
- feathers help conserve body heat
- higher temps permit metabolism of birds flight muscles to proceed at rapid pace
Explain the hair of mammals:
- All mammals have hair
- fur and endothermy allowed mammals to move into colder climates
- hair serves as camouflage
- hairs can function as sensory structures
- hairs can serve as defensive weapon
Mammal mammary glands
- Found in all female mammals
- secrete milk (high-calorie food to support rapid growth of newborn mammals)
Endothermy in mammals
- mammals can be active any time of day or night
- endothermy depends on more efficient blood circulation and more efficient respiration.
Most mammals carry young internally in a ____ and nourishment takes place through the _____.
Mammals give birth to ______
You can determine the diet of mammals by looking at _____.
Meat eating mammals have ______-like teeth and triangular molars and premolars for tearing off pieces of flesh.
Herbivores have ___, ____-like incisors for cutting off vegetation and flat, rigid molars for grinding tough plant tissues.
Mammals don’t have the proper enzymes to break down _____ and must depend on bacteria to do the job.
- cows, buffalo, deer, etc
- have four-chambered stomach that acts as fermentation vat, bacteria in one of stomach chambers break down the cellulose.
Rodents, horses, rabbits, elephants, etc., have relatively small stomachs and plant material is digested in the _____ ______.
- Large intestine.
- The bacteria that breaks down cellulose if found in the cecum.
Hooves and horns in mammals are made out of _____.
______ protect the toes and cushion them from impact.
____ are made of a bony core surrounded by sheath or keratin; bony core attached to skull.
True or False: Horns are shed seasonally
False. Horns are NOT shed
Antlers are made of _____. Deer grow and shed a set of antlers every year; while growing in the summer, they are covered by thin layer of skin called ____.
Flying mammals... aka?
Batwings are modified ____.
How did the much improved mammal ear develop from the therapsids?
Two bones forming the therapsid jaw joint moved to middle ear of mammals and joined with a bone already there. Resulted in a three boned structure that amplifies sound much better than in reptiles.
How did mammals most likely survive the period when the extinction of dinosaurs and marine animals occurred?
Because their fur acted as insulation
Modern mammals are place into three groups:
- 1. Monotremes
- 2. Marsupials
- 3. Placental mammals
Modern mammal class 1: Monotremes
- egg-laying mammals
- Platypus and echidna
- lay shelled eggs
- have cloaca(one hole for all excrement)
Modern mammal class 2: Marsupials
- Pouched mammals
- different pattern of embryonic development
- fertilized egg surrounded by chorion and amniotic membranes but no shell forms
- nourished by yolk in egg
- short-lived placenta forms before birth
- within 8 days of fertilization, embryonic marsupial born
- crawls into pouch and latches onto mammary nipple where it continues developing.
Embryonic marsupials are born within ___ days.
Modern mammals class 3: Placental mammals
- placenta nourishes embryo through entire development period in uterus
- chorion and allantois form placenta
- young undergo considerable development before birth
___ and ___ form the placenta in modern placental mammals.
Chorion and allantois
Primates share two main innovations:
- 1. Grasping fingers and toes (opposable thumb)
- 2. Placental mammals
Which vertebrates have internal fertilization?
- Cartilaginous fish (sharks)
- Order urodela (caudata) of amphibians: newts and salamanders
- Caecilians (order apoda of amphibians)
- Modern reptiles and mammals
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