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