Animals II: The Chordates

Phylum : Chordata

Subphylum: Urochordata:

Tunicates

Cephalochordata:

Lancelets

Vertebrata:

Vertebrates

Chordate Characteristics

Four traits of chordate embryos:

Notochord: stiff but flexible connective tissue, extends the

length of the body and supports it

Dorsal, hollow nerve cord

Narrow gill slits across the wall of the pharynx

Post anal tail

Most chordate species are vertebrates (endoskeleton)

Bilaterally symmetrical, coelomate animals

Complete digestive system and closed circulatory

system

Invertebrate Chordates

Lancelets: have a

fishlike shape and

retain the defining

chordate traits into

adulthood

Tunicates: lose

most of the

defining

chordate traits

during the

transition to

adulthood

Evolution of the Vertebrates

The earliest fossils of fishes date back to about

530 million years ago

Tapered body, a few centimeters long

Head with a pair of eyes, but no jaws

Skeleton consisted of cartilage

Earliest Lineages of Vertebrates

Fishes

Class Agnatha/Jawless Fishes

Modern jawless fishes

Cartilage skeleton and a cylindrical body

about a meter long

No fins

Hard mouthparts

Hagfishes and lampreys

Most primitive

craniate/ Lack jaws &

vertebrae

Notochord gives the

main support

Scavenge dead or dying

animals

Almost blind/excellent

sense of smell

Slime!

Tie their tail into a knot

Hagfishes

Lampreys: Vertebrates without hinged jaws

Larval stage

resembles the

lancelets

Suspension

feeders

Adults are mostly

parasitic

Hypothesis: jaws evolved from skeletal rods

supporting the gill slits

Evolution of the jaws

Class: Chondrichthyes/ Cartilaginous Fishes

Flexible skeleton made of

cartilage to reduce weight

Many are predators with

powerful jaws and knife-like

teeth, fast swimmers

Sharp vision and strong

sense of smell

Sensory organs along the

sides of the body that detect

prey

Cloaca

Osteichthyes

have a swim

bladder (gas

filled sac) used

to regulate

buoyancy

Class: Osteichthyes/ “Bony Fish”

Class Amphibia

First tetrapods

Scaleless

Limbs that support weight on land

Lungs

All are carnivores

Three-chambered heart

Generally tied to water/Most lay eggs in

water

Most are found in damp habitats (skin helps

supplement oxygen intake)

Salamanders, newts, frogs, toads and caecilians

Metamorphosis: Gills and tail

absorbed, terrestrial adaptations

developed

Amniotes

Amniotes branched off from an amphibian

ancestor about 300 million years ago

Traits that adapt them to life in dry places:

• Lungs throughout life, skin rich in keratin,

well-developed kidneys, fertilization within

female’s body, embryo encased in fluid

p406

Class Reptilia

Lizards, snakes,

turtles, crocodiles,

and birds

Most nonbird reptiles

are ectotherms

Nutrients from the yolk and water from the albumin in

the egg sustain the developing embryo

Terrestrially Adapted Egg

Class Reptilia/ Birds

Endothermic

Only animals with feathers Excellent vision, large brains, complex behaviors Elaborate courtship displays Hard shell eggs

Adaptations to reduce weight: no teeth, tail supported by only a few vertebrae, feathers with hollow shafts, honeycomb bone structure

Flight Adaptations

Class Mammalia

Mammary glands

Hair or fur

High metabolic rate

4-chambered heart

Long parental care

Most offspring born rather

than hatched

Endothermic

Different shape teeth

Class Mammalia

Three major lineages

Monotremes

Marsupials

Eutherians

Australia, New Guinea: platypus & spiny anteater

Monotremes: Egg-laying mammals

The young licks up milk secreted from mother’s fur

Marsupials: Pouched mammals

Brief gestation, babies born very early in development

and stay in pouch/ nurse in the pouch

Eutherians: Placental Mammals

Long pregnancy – embryo completely develops inside

mother

Complex placenta to protect and nourish developing young

Primates

Primates: placental mammals that includes humans,

apes, monkeys, and their close relatives

Shoulders have extensive range of motion

Most have both hands and feet capable of grasping

(not humans)

Most have eyes that face forward

Large brain

Social groups that include both sexes

Females give birth to one or two young at a time

Anthropoids/

Active during the day

and have good color

vision

Modern Subgroups of

Primates

Lemurs: oldest

lineage; active

during day

(tropical Africa

and southern

Asia)

Tarsiers: small,

nocturnal

(southeast Asia)

New world

monkeys (central

and South America)

and old world

monkeys (Africa and

Asia)

Apes: tailless

primates/ gorillas

and chimpanzees

Several species related to

Homo sapiens (only

surviving species)

Homo nearderthalensis

Homo erectus

Homo habilis

Australopethicus sp.

Hominins

Order: Primates

Suborder: Anthropoid

Family: Hominidae

Tribe: Hominini

Bipedalism:

Habitual upright

walking

Evidence of bipedalism in early hominins

Early Hominins

Sahelanthropus tchadensis

may be the oldest hominin

(7 mya)

Ardipithecus (5.8-5.2 mya)

and Australopithecus (4-

1.2 mya)

Australopithecus sediba

Genus Homo

Ancestors of humans originated in Africa Oldest known fossils of Homo sapiens are from Ethiopia (160,000 and 195,000 years old) Coexisted with other Homo species including H. neanderthalensis and H. floresiensis

Modern humans have a number of distinctive physical features

including:

large brain volume/ 1,300 cm3

lightly built skeleton, adapted to walking on 2 legs

skull with a short base and a high braincase

small or absent brow ridge

chin on the lower jaw

Lack thick coat of body hair

Precision grip