Zoology Chapter 15.6

Vertebrates

vertebral column

replaces notochord

protection of spinal cord

stronger support

larger body size possible

improved movement

jawless fish (agnatha)

most basal living vertebrates

vertebrate and cartilogenous skeletons

lack jaws

no paired fins

eel-like body shape

ex: lampreys, hagfish

gnathostomes

jaws evolved from modified gill arches

developed from Agnatha

active predation

larger prey capture

more efficient feeding

increased energy intake

diversification of diet

cartilaginous and bony fish

cartilagenous fish

jaws and paired fins

skeleton made of cartilage

placoid scales

ex: sharks, rays

bony fish

jaws and paired fins

skeleton made of bone

operculum covering gills

usually possess a swim bladder

ray-finned fish and lobe-finned fish

operculum

sheilds openings, protect organs and structures

swim bladder

an internal gas-filled organ that allows them to control buoyancy so they can maintain depth without having to swim all the time

lungs

evolved from ganthostomes

evolved BEFORE life moved on land

tetrapods

four limbs

evolved from lungs

bone structure inside fin → humerus, radius and ulna, and distal bones

weight support

movement onto land

new habitats available

amphibians

early terrestrial tetrapods

developed from tetrapods

4 limbs

moist, permeable skin

lungs, respiration through skin

reproduction depends on water

undergo metamorphosis → limbs and lungs develop

amphibians

major groups: salamandars and newts, frogs and toads, caecilians

salamandars and newts

major amphibian group

usually retained in adult

frogs and toads

amphibian major group

lack tail, powerful hind legs for jumping

caecilians

amphibian major group

legless, burrowing, ressemble worm

their skin, eggs, and early life stages require moisture to function

why do amphibians remain dependent on waiter

amniotes- amniotic egg

developed after amphibians

an egg that creates a self-contained “aquatic environment”, allowing embryos to stay moist, protected, and nourished

structures: amnion, allantois, chorion, yolk

fluid cushion

amnion function

gas exchange

chorion function

waste storage

allantois function

nutrition

yolk functions

reptiles, birds, and mammals

vertebrate groups that are amniotic

reptiles

developed after amniotes

internal fertilization

dry, keratinized skin (limits water loss)

improved lungs

amniotic egg

ectothermic

excretion of uric acid (conserves water)

reptiles

crocodiles/alligators, tuataras, snakes and lizards, turtles and tortoises

birds

developed after reptiles

adaptions: wings, feathers, hollow bones, highly respiratory system, air sacs

archaeopteryx

mix of dinosaur and bird traits

earliest primitive bird

evolved within reptile lineage

mammals

Developed after birds

hair and mammary glands

hair or fur during some point in development

endothermic

most have specialized teeth

three middle bones

hair and mammary glands

two defining mammalian characteristics

mammals

major groups: monotremes, marsupials, placental mammals

monotremes

mammal major group

lay eggs

ex: platypus

marsupials

mammal major group

give birth to very underdeveloped, continues in pouch

ex: kangaroos and opossums

placental mammals

mammal major group

embryo develops with a complex placents

ex: wolves

ROOT (Chordates)
│
├── Outgroup (Tunicates / Cephalochordates)
│
└── Vertebrata — vertebrae appear [node]
│
├── Jawless Vertebrates (Agnatha)
│ ├── Hagfish
│ └── Lampreys
│
└── Gnathostomata — jaws appear [node]
│
├── Chondrichthyes — cartilaginous skeleton [node]
│ (Sharks, Rays)
│
└── Osteichthyes — bony skeleton [node]
│
├── ray‑finned fishes
│
└── lobe‑finned fishes [node]
│
└── Tetrapoda — four limbs [node]
│
├── Amphibia — lungs + aquatic larvae
│
└── Amniota — amniotic egg [node]
│
├── Reptilia — scales, ectothermy
│
├── Aves — feathers, endothermy
│
└── Mammalia — hair, milk glands