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- belong to the clade: Deuterostomia

Derived Characteristics of Chordates

Dorsal Hollow Nerve Cord
Pharyngeal gill slits
Post-anal tail


long, flexible rod located between the digestive tube and nerve cord
- provides skeletal support through the length of the animal

Dorsal hollow nerve cord

-located dorsally to the notocord
- develops into the CNS - brain and spinal cord

Pharyngeal gill slits

slits that develop in the pharnx that open to outside of the body
- used for gas exchange in aquatic chordates
- becomes parts of the ear in tetrapods

Post anal tail

tail that extends beyond the anus
- reduced in embryonic development


most basal chordate group
- Cephalochordata
- have blade-like body shape
- wriggles body into the sandy sea floor with only the mouth exposed for capturing plankton in the water
- have muscle segments along its body called somites
- amphioxus


- larva stage has the 4 characteristics of chodates
- draw in water through an incurrent siphon, then it passes thru the pharyngeal slits into a chamber called the atrium and then out thru a excurrent siphon
- aka sea squirts
- undergoes pedogenesis- larva reproduces

Developmental genes in lancelets and chordates

- they have the same Hox (homeobox) genes (BF1, Otx, and Hox3) that controls the development of major regions of the vertebrae brain
- the genes are expressed in the same order too
- homeobox genes- genes that control the expression of other genes


chordates with a head
- brain at anterior end with dorsal nerve cord, eyes, sensory organs, and a skull

Derived Characteristics of Craniates

- 2 or more sets of Hox genes
- Neural crest
- higher metabolic rate and more extensive muscular system
- heart with at least 2 chambers
- RBC's, kidneys, etc.

Neural crest

collection of cells that appears near the dorsal margins of the closing neural tube of an embryo
- a type of stem cell line
- these cells will migrate to distant sites of the embryo
- migrating cells give rise to teeth, bones/cartilage of the skull, inner layer of skin of the facial region, neurons and sense organs


-most primitive craniate fossil found
- formed 350 mya during Cambrian explosion
- resembeled a lancelet


- most basal craniate group
- skull made of cartilage; no jaws or vertebrae
- retain notocord in adulthood, swim like an eel
- mouth contains teeth made of keratin
- marine- deep water
- produce large slime coats from slime glands

Derived Characteristics of Vertebrates

- gene duplication of Dlx transcription factor genes
- more extensive skull and backbone
- vertebrae enclose the spinal cord
- more efficient gas exchange in the gills


- basal lineage of vertebrates
- parasites that feed by clamping on the sides of fish with their mouths
- no jaws --> sharp teeth made of keratin


"cone teeth"
slender soft-boded vertebrates with large eyes and barbed hooks at the end of their mouth
- does not have jaws
- hooks were dental mineralized dental tissue - used for predation or scaveging


armored agnathostome fish that had plated armor over their bodies
- armor was made of mineralized bone = cosmoid-dentine
- evolutionary origin of bony, mineralized teeth


jawed vertebrates
- have teeth that enable them to grip food

Hypothesis for the evolution of vertebrate jaws

skeleton of the jaws may have evolved from two pairs of skeletal rods located between gill slits near the mouth
- pairs of rods anterior to these were lost into the cranium or jaws over time
- remaining gill slits, behind the jaws, become the site of respiratory gas exchange
- shark teeth is made of placoderm - jaw articular is hyostyly
- humans jaw articulation is autostyly

lateral line system

organs that form a row along each side of the body and are sensitive to vibrations in the surrounding water
- found in aquatic gnathostomes


-plate-skinned jawed fish
- the first fossil of gnathostomes
ex: Amia


group of jawed vertebrates that emerged during the Devonian period


Sharks, rays, and their relatives --> ratfish (chimera)
-cartilaginous fish
- 7 gill arches


sharks lay eggs that hatch outside the mother's body


females retain the fertilizd eggs in the oviduct
- young are born after hatching within the uterus


the young develop within the uterus and obtain nourishment prior to birth by receiving nutrients from the mother's blood through a yolk sac placenta


common chamber that has a single opening to the outside


- have ossified (bony) skeleton with a hard matrix of calcium phosphate
- skin is covered in flattened scales
- oviparous
- 5 gill arches


protective bony flap covering the gills of bony fish
- water is drawn into the mouth, through the pharynx, and out between the gills by movement of the operculum

Swim Bladder

how fish control their buoyancy with this air sac
- movement of gasses from blood to swim bladder increases buoyancy
- transfer of gas back to the blood causes the animal to sink

Ray finned fishes

have bony rays that support their fins

Lobe finned fishes

rod shaped bones surrounded by a thick layer of muscle in their pectoral pelvic fins
- coelacanths and lungfishes


"four feet" vertebrate
- fins evolved into limbs


- a fish with fin, gills, lungs, and scales
- had full set of ribs- helped support its body and aided in it breathing air
- had a neck and shoulders
- also its front fin had bones resembling bones in the tetrapod forearm
- this fossil is the link to tetrapods - the transitional organism


Class Amphibia
salamanders, frogs, caecilians
- have tadpole larvae stage
- most have four legs, moist skin, lay eggs in water

Order Urodela


Order Anura


Order Apoda

- has no legs --> look like segmented worms


reptiles, birds, and mammals
- have an amniotic egg
- use their rib cage to ventilate their lungs

Amniotic egg

four specialized membranes: amnion, chorion, yolk sac, and allantois
- have a shell- either hardened or soft- reduces dehydration
- this is a major step in evolution: it allowed the embryo to develop on land so reduced the dependence on water sources by tetrapods for reproduction


exchange gases between the embryo and the air
- oxygen and carbon dioxide diffuse freely across the shell


protects the embryo in a fluid-filled cavity that cushion against mechanical shock


disposal sac for metabolic wastes produced by the embryo
- function with the chorion as a respiratory organ

Yolk sac

contains yolk (used for nutrients)
- blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo
- other nutrients (protiens) are stored in the albumen


tuataras, lizards, snakes, turtles, crocodilians, birds
- have scales., lay shelled eggs


tuataras, snkes, lizards


Animals that absorb external heat as their main source of body heat
ex: reptiles
- can survive on 10% of the food that a mammal of the same size would require


animals capable of maintaining near constant body temp. through metabolic activity
- bird, mammal

Derived Characteristics of Birds

-flight- many weight saving
- lack a urinary bladder
- females only have 1 ovary
- toothless
- feathers- derived from keratin

Origin of Birds

evolved from dinosaurs about 150 mya
- Archaeopteryx- earliest bird fossil --> the link to dinosaurs
- it had teeth, claws, but also had wing feathers and long tail with feathers
- thecodonts vs theropods theory


Order Struthioniformes
- flightless birds
- emu, ostrich, kiwi, rhea, cassowary
- sternal keel is absent
- smaller pectoral muscles


Class Mammalia

Derived Characteristics of Mammals

- mammary glands
- endothermic
- diaphragm - muscle that aids in breathing
- larger brain than other vertebrates of equal size
- long duration of the care of young
- differentiated teeth (incisors, canines, pre-molars, molars)
- dentary/squamosal jaw articulation


- mammals
- single temporal fenestra
- two of the bones that formerly made up the jaw (articular & quadrate), now are part of the inner ear --> adds mechanical amplification of sound
- mammals have dentary/squamosal articulation

When the did the first true mammals arise?

During the Jurassic period ( 200-145 mya)


- egg-layig mammals
-found only in Australia and New Guinea
ex: Echidna and the Platypus
- have hair and produce milk, but lack nipples


ex: opossums, kangaroos, koalas
- have nipples, produce milk
- higher metabolic rate; give birth to live young
- young are born early on in development and grow while nursing inside the mother's pouch = marsupium


structure in which nutrients diffuse into the developing embryo from the mother's blood
- formed from part of the lining of the uterus


placental animals
- have more complex placentas than the marsupials
- young do not develop inside a pouch
- longer pregnancy term
- young complete their embryonic development inside the uterus ; connected to mother via the placenta

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