- Vertebrates possess
and are a sub-phylum
Phylum Chordata are bilateral
animals that belong to the clade Deuterostomia.
Vertebrates are a sub-phylum within Chordata that possess a vertebral
Phylum Chordata are animals
that possess four derived traits:
- a flexible notochord
- a dorsal, hollow nerve cord
- pharyngeal slits
- a muscular, post-anal tail
The notochord is a stiff but flexible
rod between the digestive tube and the nerve cord.
In humans, it is reduced to gelatinous disks between the vertebrae.
The nerve cord is a hollow tube comprising the
central nervous system: the brain and a spinal cord enclosed by
Chordate embryos possess pouches(pharyngeal slits) in the pharynx
(region posterior to the mouth). Pharyngeal slits develop into gills
in fishes, and structures in the head, ear, and neck in terrestrial
Chordates have a muscular tail posterior
to the anus.
The tail contains muscles, and provides the propelling force in many
are chordates that have a
and includes hagfish.
Craniates have a head with a cranium (skull).
The cranium is derived from ectodermal cells called the neural crest.
Hagfish (Myxini) are jawless marine craniates that have a cartilage
skeleton, but no vertebrae.
They can produce copious amounts of slime, which they clean off by
tying themselves in a knot.
are craniates that have a
made of vertebrae.
Vertebrae are made of a series of bones that make up the backbone and
enclose the spinal cord.
are vertebrates that have
that evolved from skeletal supports of the pharyngeal
The evolution of vertebrate jaws.
The skeleton of the jaws and their supports evolved from two pairs of
rods skeletal rods located between gill slits near the mouth.
with a skeleton
Chondrichthyes have a skeleton made of cartilage.
Blacktip reef sharks are fast swimmers with paired pectoral and pelvic
fins. Stingrays are bottom-dwellers that crush molluscs and
crustaceans. Manta rays cruise in open water and scoop food into their
mouth. Spotted ratfish feed on shrimps, molluscs, and sea urchins.
Some species have a poisonous spine at the front of their dorsal fin.
are fish with a
Osteichthyes have a bony endoskeleton. They control buoyancy with a
swim bladder, and breathe through gills that are covered by a flap
(operculum). A lateral line allows fish such as sardines to sense
vibrations in the water and change directions in synchrony.
fishes) have fins supported by bony spines ("rays").
The fins are adapted for maneuvering, defense, and other functions.
are lobe-finned fishes with more muscular pelvic and pectoral fins
and include coelacanths
Coelacanths live in deep ocean, and were thought to be extinct until
discovered in 1938.
They form one of only two surviving lineages of aquatic lobe-fins.
Lungfishes (order Dipnoi) have a modified swim bladder that allows
them to breathe air.
- Tetrapods are Gnathostomes that have
limbs, and evolved from lobe-finned
fish whose fins developed into limbs
adapted for terrestrial life.
Acanthostega from the Devonian period (365 MYA) had limb-like fins but
also retained aquatic adaptations such as gills.
Tetrapods evolved from similar members of the bony fishes called
The origin of tetrapods.
Tetrapods are terrestrial vertebrates with four legs.
A great diversity of tetrapods emerged during the Devonian and
from aquatic larva into a terrestrial
Amphibia lead "two ways of life". Fertilization is external, and the
eggs require a moist environment.
Aquatic larva undergo metamorphosis to develop into a terrestrial
Most amphibians have moist skin that complements the lungs in gas
- There are
are frogs and toads, and
Order Urodela (salamanders) retain their tail as adults. Order Anura
(frogs) lack a tail as adults. Order Apoda (caecilians) are legless,
mainly burrowing amphibians.
that have an
egg adapted for terrestrial life.
- Diapsids (most reptiles, including birds),
- Synapsids (mammals are sole living members).
The amniotic egg contains several membranes that allowed animals to
live a fully terrestrial life style.
- The amnion protects the embryo in a fluid-filled cavity that
serves as a cushion.
- The allantois holds metabolic wastes produced by the embryo.
- The chorion exchanges gases between the embryo and the air.
- The yolk sac provides nutrients; other nutrients are stored in the
albumen (egg white).
- Living reptiles
There are over 4,000 species of extant lizards, making them the most
diverse reptiles, apart from birds. Horned lizard:
Snakes evolved from lizards. Some snakes such as pythons and boas
retain primitive limbs.
The shell of turtles is made of an
upper carapace and lower plastron.
This species is sold in pet shops, but not native to northern
Emu. This Australian bird has no keel on its sternum and cannot fly.
Mallards exhibit strong sexual dimorphism between the sexes. Many
birds have specific courtship rituals. Laysan albatross: Barn swallows
are perching birds; the toes can lock around a branch or wire.
are the only surviving clade of
among the amniotes.
Class Mammalia contains 20 orders of
animals, including humans.
Mammals possess hair (or fur) and produce milk from mammary glands.
are the only mammals that lay
Monotremes such as this echidna have hair and produce milk, but lack
nipples and lay eggs.
The milk is secreted by glands on the belly of the mother, and the
baby sucks milk from the fur.
Monotremes are only found in Australia.
complete embryonic development within a maternal pouch
Marsupials belong to the Chordate class
Mammalia that are born early and complete embryonic development within
a maternal pouch (marsupium).
Many marsupials in Australia resemble eutherians elsewhere that occupy
similar ecological niches due to convergent evolution.
The young of marsupials (such as this brushtail possum) are born early
in their development. They finish their growth nursing from a nipple
in their mother's pouch, or marsupium. Bandicoots have rear-opening
pouch to protect the young from dirt as the mother digs.
Marsupials are mainly found in Australia, though North America does
have one species.
mammals that complete their embryonic development within a
joined to the mother by the
are a branch of
and include monkeys
Primates have opposable thumbs adapted for grasping.
Anthropoids began diverging from other primates about 50 million years
The human lineages branched off from our closest relatives about 5 to
7 million years ago.
New World monkeys such as this spider monkey have a prehensile tail
adapted for grasping; their nostrils that open to the sides. Old World
monkeys such as this macaque lack a prehensile tail; their nostrils
Hominoids (or apes) include:
are more closely related to humans than to chimpanzees and originated in
about 6-7 million years ago.
- Lucy, a 3.24-million-year-old skeleton, represents the hominin
species Australopithecus afarensis.
- The Laetoli (Tanzania) footprints, more than 3.5 million years
old, showed that early hominin could walk upright.
- An artist's reconstruction of what A. afarensis looked like.
- The Homo genus
slowly became more fully
and evolved a large
The Homo lineage.
- Homo habilis
- Homo ergaster
- Homo erectus
- Homo neanderthalensis
- Homo sapiens may be the only animals capable of symbolic thought.
Exercise: Human evolution
Homo neanderthalensis lived in
Europe and the Near East from 200,000 to 30,000 years ago.
There may have been limited gene flow between Neanderthals and H.
sapiens before the former became extinct.
The oldest known fossil of Homo
sapiens suggests that we first appeared in Africa about 160,000 years
Art, a human hallmark.
The engravings on this 77,000-year-old piece of ochre are among the
earliest signs of symbolic thought in humans.
Are birds capable of symbolic thought?
Alex the talking parrot
Betty the crow
Summary: Characteristics of chordates