Chapter 34: The Origin & Evolution of Vertebrates

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Chordates
triploblastic, eucloemate, bilateral symmetry deuterosomes; marine, freshwater and terrestrial habitats

- other general characteristics:
extracellular digestion with complete digestive tract, segmentation, closed circulatory system and well-developed respiratory systems, well-developed nervous system with brain, most are dioecious, radial cleavage and indeterminate cleavage, advanced excretory systems
Four Key traits of Vertebrates
1. notochord
2. pharyngeal gill slits
3. dorsal, hollow nerve chord
4. post-anal tail
Vertebrate History
1) 530 million (Cambrian Period)
years ago, invertebrate
animals inhabited oceans
2) One type of animal gave rise to vertebrates
- vertebrates get their
name from vertebrae, the
series of bones that make
the backbone
notochord
a flexible rod running posteriorly from the head to the tail

it provides attachment site for muscles and a support structure that can bend

consists of large fluid-filled ells encased in a stiff cartilaginous like connective tissue
pharyngeal gill slits
in primitive chordates, slits that open to the outside; allow water to leave the digestive tract before entering the stomach and intestines

in invertebrate chordates, function in filter feeding

adapted for other purposes in higher vertebrates such as the Eustachian tubes and middle ear bones
Dorsal, hollow, single nerve chord
develops the brain and spinal chord of the central nervous system
post-anal tail
a tail of variable length that extends past the anus

contains skeletal structures and muscles, and it provides a major means of propulsion for some chordates
Lancelets
+ Cephalochordata
+ bladelike shape
+ retain characteristics of
the chordate body plan
as adults
- marine filter feeders; cilia on the tentacles (cirri) draw water into the mouth
- definite segmentation with chevron-like muscle blocks; no 'brain'
- can swim as adults, swim by the movement of caudal fin; use notochord for swimming and burrowing
- rudimentary circulatory system, lack a heart and capillary beds, blood lacks blood cells and hemoglobin
- dioecious with external fertilization
Subphylum Urochordata/Tunicates
tunicates (marine) or sea squirts

Characteristics:
1. lose their notochord as adults and become sessile filter feeders, some are pelagic (open water species that float through the open ocean)
2. pharynx expands into a basket-like structure in the adults
3. larval tunicate resembles the larval or adult stages of other chordates, & possess all four major chordate characteristics
4. outer body covering- the Tunic (made of cellulose-like carbohydrate, tunicin), secreted by the epithelium
5. water --> incurrent (oral) siphon --> gill slits of the basket-like pharynx --> large atrium --> leaves via the outcurrent (atrial) siphon
6. no special respiratory system, open circulatory system
7. monoecious with external fertilization
subphylum vertebrata
largest of chordate groups

general characteristics:
1. nerve chord and notochord and neural crest
2. neural crest form nerves, parts of the cartilage, and bones of the skull, teeth, jaws and other
3. vertebrate made of bone (or cartilage)
4. living endoskeleton that grows with the animal
5. integument that consists of inner dermis and outer epidermis
The Hagfishes, Class Myxini
hagfish
oldest living group of vertebrates

general characteristics:
1. marine benthic predatory/ scavengers that feed on a variety of invertebrates and dead fish; rasping tongue with teeth
2. skeleton composed of cartilage
3. lack jaws, rudimentary vertebrate
4. tubular eel-like body with many slimy glands on their naked skin
5. no paired appendages
6. a brain, small or degenerate eyes, one pair of semicircular canals
7. circulatory system with hearts and gills for respiration; body fluids are iso-osmotic with seawater
8. large, yolky eggs but not independent larval stage
the Lampreys, Class Petromyzontida
Lampreys

General characteristics:
1. larvae show all four chordate characteristics, larvae for long periods of time --> develop into short-lived parasitic adults
2. larvae are suspension feeders, feeding on plankton and detritus
3. two-chambered heart, a three part brain, thyroid and pituitary glands; kidneys are similar to higher vertebrates
4. notochord that becomes partially enclosed by cartilaginous sheath
5. law jacks and paired appendages
6. circular mouth with keratinized teeth, rasping tongue
7. well-developed eyes and a more advanced brain; two pairs of semicircular canals
8. efficient kidneys with body fluids osmotically and ionically regulated
9. 7 pairs of gills for respiration, closed circulatory system consisting of two chambers
The Gnathostomes
general characteristics:
1. jaws and teeth; expansible and mobile oral cavity
2. paired limbs
3. three pairs of semicircular canals
4. well-developed brains with advanced sensory organs
The Jawed Fishes
made up of Chondrichthyes and Osteichthyes

Characteristics:
1. use gills for respiration
2. reproduction: oviparous, ovoviviparous, and viviparous
3. closed circulatory systems including a heart with two chambers and have a single loop to their circulation
4. unable to synthesize the aromatic amino acids (tyrosine, tyrptophan, phenylalanin), so these amino acids must be supplied in food
The Cartilaginous Fish, Class Chondrichthyes
sharks, skates, rays, and relatives

general characteristics:
1. cartilaginous endoskeleton, placoid scales; among one of the first groups to develop teeth
2. tail provides propulsion, with the fins are stabilizers;
placoid scales
tooth-like cartilaginous scales
oviparous
lay eggs that hatch externally
ovoviviparous
lay eggs that hatch in the female's reproductive system
viviparous
bear live young; there are no 'eggs' laid initially
Bony Fishes, Class Osteichthyes
general characteristics:
1. most abundant vertebrae animals, skeleton is made of bone
2. marine and freshwater
3. swim bladders
4. gas exchange occurs by drawing water over the 4 to 5 pairs of gills covered by the operculum
5. tails and flexible fins
6. scales
7. good osmoregulators
hypotonic
environment in which freshwater fish absorb water by osmosis across thin membranes and gills

these fish actively absorb salts across the gills and create dilute urine
hypertonic
environment in which saltwater fish tend to lose water from the gills by osmosis

urine is more concentrated to conserve water
Class actionpterygii
perches, sunfishes, and catfishes

fins are supported by thin, parallel bony rays that stiffen the fin
no muscles in the fins, instead muscles are within the body of the fish
class sarcopterygii
lobe-finned fishes

long fleshy muscular lobes to their fins, the lobes contain articulated bones that are extensions of the pectoral and pelvic areas
bony rays on ends of lobes
fin rays can be moved independently by muscles inside the lobe
class dipnoi
lungfishes

can sometimes be identifies as a subclass of the Sarcopterygii class
the tetrapods
four-limbed animals
primarily freshwater and terrestrial

key general characteristics: TWO PAIRS OF LIMBS, thought to have evolved from lobe-finned fishes
Derived Characteristics:
= Four limbs, and feet with digits
= A neck, which allows separate movement of the
head
= Fusion of the pelvic girdle to the backbone
= The absence of gills (except some aquatic species)
= Ears for detecting airborne sounds
Origin of Tetrapoda
- gnathostomes that
have limbs
- Tiktaalik, nicknamed a "fishapod," shows both fish
and tetrapod characteristics

- Fins, gills, lungs, and scales
- Ribs to breathe air and support its body
- A neck and shoulders
- Fins with the bone pattern of a tetrapod limb
- 365 Mya- first tetrapods.
pulmonary circulation
the heart pumped deoxygenated blood through a pulmonary artery to the lung for oxygenation, with a pulmonary vein carrying blood back to the heart for pumping it back to the body
class amphibia
frogs, toads, and salamanders

general characteristics:
1. four limbed with usually four toes on front limbs
2. must return to water to lay their eggs; eggs lack shell
3. some have lungs, but others rely on exclusively their skin for gas exchange; skin is smooth and moist with many glands
4. good ecological indicators
5. metamorphosis
6. closed circulatory system with 3 chambers
Have moist skin that
complements the lungs in gas exchange
+ (Important) Amphibian means "both ways of life,"=
the metamorphosis of an aquatic larva into a
terrestrial adult
Urodela (salamanders)
= amphibians with tails
= Some are aquatic, but others live on land as adults
= Paedomorphosis is retention of juvenile features in sexually mature
organisms
Anura (frogs)
= lack tails
= have powerful hind
legs for locomotion on land
= leathery skin---> "toads"
Apoda (caecilians)
= legless, nearly blind, and
resemble earthworms
= The absence of legs-secondary adaptation, see classification chart
metamorphosis
from aquatic larvae (tadpoles) to terrestrial adults
Amphibian threats
- external fertilization is not so adapted to land life, requires water
- disease-causing chytrid
fungus, habitat loss, climate change, and pollution
the amniotes
+ tetrapods that have
a terrestrially adapted eggs

reptiles, birds and mammals
amniotic egg --> higher adaptation

general characteristics:
1. four extraembryonic membranes
2. closed circulatory system with 3 or 4 chambered hearts
3. eliminate urea or uric acid
4. tough leathery skin
5. strong jaw muscles
6. internal fertilization
7. more efficient circulatory systems
8. better respiratory systems
Amniote History
- Living amphibians and amniotes split from a
common ancestor about 350 million years ago
- Adapted to terrestrial life because of the amniotic sac
- Early amniotes led predatory life w/ sharp jaw to bite and long teeth
amniotic egg
shelled to prevent desiccation and has a series of extra-embryonic membranes that help the embryo develop totally inside a terrestrial egg
allantois
allows a place to store waste (other than ammonia) allows for water conservation
involved in gas exchange
chorion
involved in gas exchange from the embryo and the outside, through the shell
outermost membrane
cuts down on water loss
yolk sac
surrounds the yolk, provide nutrients for the young embryo
amnion
fourth membrane that immediately surrounds the embryo and the amniotic fluid
innermost membrane around the embryo
class reptilia
snakes, crocodiles, lizards, and turtles

general characteristics:
1. four limbed with 5 toes
2. oviparious and dioecious
3. water-proofing scales made of keratin
4. 3 chambered heart some have evolved to 4 chambered heart
5. efficient lung for gas exchange, does not rely on skin
6. ectothermic and uricotelic
7. eggs covered with calcareous or leathery shells
Turtles
have boxlike shell made of upper and
lower shields that are fused to the vertebrae,
clavicles, and ribs
- lay eggs in beaches
Lepidosaurs
- Survivor: lizard like tuatara
- threat: rats(consume their eggs)
-Other Survivor: Squamates(lizards and Snakes)-most numerous and diverse
reptiles, apart from birds
Snakes: legless, evolved from lizards, carnivorous w/multiple adaptations to catch prey:
+ Chemical sensors
+ Heat-detecting organs
+ Venom
+ Loosely articulated jawbones and elastic skin
Reptile History
- earliest reptiles
lived about 310 million years ago
- diapsids-split into lepidosaurs and the archosaurs
-The lepidosaurs- tuataras, lizards, snakes,
and extinct mososaurs
- The archosaurs -
crocodilians,
pterosaurs(flying), and dinosaurs
- Dinosaurs included bipedal carnivores called
theropods, the bird ancestor.
Reptile Bird Differences
- Reptiles are ectotherms, birds are endotherms
- Birds might have descended from dinosaurs, see above, because they showed parental care, and were endotherms
- Remember Archaeopteryx
- Most Dinos were killed in cretaceous period due to asteroid, but birds survived.
Crocodilians
Archosaurs- alligators and crocs.
- generally in warm areas
class aves/birds
evolved from reptilian ancestors

general characteristics:
1. feathers, hind legs covered in scales, usually 4 toes
2. endotherms and ovaiparous, dioecious, and uricotelic
3. four chambered heart, air sacs to help support endothermy and an active lifestyle
4. homoplasy of 4 chambered heart and endothermy in mammals
5. nucleated blood cells
6. single bone in middle ear; horny sheaths on jaw forming the beak; no teeth
Bird History
- 160 million years ago, descended from small theropods, a
group of carnivorous dinosaurs
- Early feathers might have evolved for insulation,
camouflage, or courtship display
- Archaeopteryx remains the oldest bird known, with a toothed beak, winged claw, and long tail w/ many vertebrae.
Flightless Birds
- Ratites (order Struthioniformes)= think of your fav bio tutor(Sruthi)
- Penguins, order Sphenisciformes
- Some rails, ducks, and pigeons
class mammalia
thought to have come from the reptile line

general characteristics:
1. dry, leathery skin and hair
2. sweat glands used for thermoregulation
3. mammary glands that produce milk
4. teeth are modified for different functions
5. 3 inner ear bones
6. secondary palate separating the trachae and the esophagus
7. muscular diaphragm that helps ventilate the lungs
8. endothermic with a 4 chambered heart; non-nucleated biconcave red blood cells
9. dioecious; some lay eggs and some give birth to live young
Mammal History
- Mammals are synapsids
-two bones that formerly made up the jaw joint in early synapsids
were incorporated into the mammalian middle ear
- 3 lineages of mammals:
monotremes, marsupials,
and eutherians
hair
present in mammals
involved in insulation, camouflage, protection and sensory organs
monotremes
similar to reptiles
have just one opening (the cloaca) that combines the anal opening to the digestive tract, the ducts of the excretory system and the genital ducts
lay shelled eggs that are hatched outside of the body
resemble reptiles in the structure of the eye and presence of certain skull bones
marsupials
pouched mammals
viviparious, do not have long gestation times
give birth very early and helpless embryo climbs from the mother's birth canal to the nipples in the pouch
young embryo holds onto nipple with its mouth and continues to develop in the pouch for several weeks to several months
placental
viviparous species
nourish embryos with mother's blood supply which allows longer gestation period
young nurse milk off of mother
Primates
- lemurs,
tarsiers, monkeys, and apes
- Humans are members of the ape group
- Derived Traits:
= A large brain and short jaws
= Forward-looking eyes close together on the face,
providing depth perception
= Complex social behavior and parental care
= A fully opposable thumb (in monkeys and apes)
Anthropoids
-monkeys and apes
- oldest known anthropoid fossils, about 45
million years old, indicate that tarsiers are more
closely related to anthropoids than to lemurs
Monkey and Ape History
+ The first monkeys evolved in the Old World (Africa
and Asia)
+ In the New World (South America), monkeys first
appeared roughly 25 million years ago
Both underwent adaptive radiations during their many millions of years of
separation(Genetic Drift due to geographic barrier)
APES:
- includes gibbons, orangutans, gorillas,
chimpanzees, bonobos, and humans
-diverged from Old World monkeys about 25-
30 million years ago
Humans
- have large brain+bipedal locomotion!
- species Homo sapiens is about 200,000 years
old
-Derived Traits:
+ Upright posture and bipedal locomotion
+ Larger brains capable of language, symbolic
thought, artistic expression, the manufacture and
use of complex tools
+ Reduced jawbones and jaw muscles
+ Shorter digestive tract
- Humans and Chimps have 99% DNA similarity!
- Most changes in genomes are in hox genes ( regulatory)
paleoanthropology
The study of human origins
Early Hominin
-more closely related to humans than to chimpanzees
-There are fossils of 20 species of extinct hominins, starting from 6.5 million yrs ago.
- Had small brains
- Human evolution is not like a ladder, it has many coexisting branches.
Australopiths
2 to 4 mya
- Australopithecus afarensis
walked fully erect!
Two types:
a) Robust:sturdy skulls and
powerful jaws
b) Gracile:slender and had
lighter jaws
Tool Use
+started 2.5 million years ago
Bipedalism
+started 1.9 million years ago
+energy efficient locomotion
Early Homo
The earliest fossils placed in our genus Homo are
those of Homo habilis, who is called Handy Man bc he had tools, and these fossils range in age from about
2.4 to 1.6 million years
-Homo ergaster = the first fully bipedal, large brained
hominid, existed 1.9 and 1.5 million
years ago, and shows decrease in sexual dimorphism.
Homo erectus: 1.8 mya, origin in Africa but it is the first hominin to leave africa.
Neanderthals
+ Homo neanderthalensis, lived in
Europe and the Near East from 350,000 to 28,000
years ago
+ Features: thick-boned with a larger brain, they
buried their dead, and they made hunting tools
+ gene flow occurred bw them and Homo sapiens
Homo Sapiens
Homo sapiens appeared in Africa by 195,000
years ago
- Outside of africa, first fossils found in middle east
-In 2004, 18,000-year-old fossils were found in
Indonesia, and a new small hominin was named:
Homo floresiensis
- Had symbolic and sophisticated thought

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