Chapter 26: Animal
evolution- The Chordates
Ruth Cuaboy
Characteristics of Chordates
1. Notochord; connective tissue extending along body. To provide
support.
2. Dorsal: Nerve cord.
3. Gill slits: along the throat(pharynx)
4. Muscular tail: extending tail beyond the anus.
Invertebrate Chordates
Lancelets (subphylum cephalochordata); They miss a brain case , and paired
sensory organs. They filter food from water and their cilia allows them to
move. There segmented muscles allow them to swim short distances.
Tunicates(subphylum urochordata); Are larvae with chordate traits. The
only characteristics they end up from chordates are the pharynx and the gill
slits. Tunicates also filter food from water. The water enters through their
mouth its passes through he slits and sticks to the mucus and gets sent to
the gut.
Craniates; have brain case to support the brain. Have paired eyes and
sensory structures in the head. For example the hagfish has a notochord
which supports the body, have paired eyes that detect vibrations. Use
vibrations the most since their vision is poor.
Lancelet
hagfish
Tunicate
Vertebrate evolution
Amphibians
Major classes of vertebrates
Jawless lampreys:
Larval lampreys ;have no jaws or fins. Have a backbone of cartilage.
They all undergo metamorphosis.
They burrow into the sediments and filter food from the water.
Parasitic lamprey; have an oral disk. They attach to the host and the host later dies
of blood loss or infection.
Most remain in fresh water and the parasitic lampreys migrate to sea.
Jawed fishes
Jawed fishes; have paired fins and scales. Hard structures
grow and cover the skin.
Two groups of jawed fishes
1. Cartilaginous fishes; all have a skeleton of cartilage and gill slits.
teeth are modified scales that harden.
Ex; marine sharks and rays.
Bony fishes
Bony fishes; Bones replace cartilage. Have an operculum which is a cover that
protects the gills.
Have a swim bladder which is a gas filled device that adjusts the volume of gas
which enables the fish to be in water at different depths.
Subgroups:
1. Ray finned fishes; Have flexible fin support derived from skin. Are the most
diverse fishes.
ex: teleosts , sea horses
Lung fishes; bony fishes that have gills and lung like sacs. They have outpouchings
of the gut wall. They fill the sacs by gulping air and the oxygen diffuses from sacs to
blood.
Coelacanths; there ventral fins are fleshy extensions of the body wall. Are a
modern group of lobe finned fishes.
Early primates
Amphibians
• Need water to breed and have 3 chanber hearts.
•Branched off the lobe finned fishes.
•Adapted to swimming into four legged walkers(tetrapods).
•Division in the heart to two circuits one to body and the other to lungs.
•Modern amphibians: salamanders, caelians,, frogs/toads.
salamander; walk with body bent like a swimming fish which means ancestors had
the same way of walking.
Caecilians; burrow through soil and use touch and smell to catch prey.
Frogs/toads; elongated hind legs for leaps and swimming.
Cenozoic era
Starts off with amniotes. They make eggs having four membranes that allows embryos to develop
away from water. Also had waterproof skin and kidneys.
3 remaining groups; turtles, lizards/snakes, crocodiles/birds.
Reptile: No traits of birds or mammals.
Early reptiles; lizard like body and waterproof scales.
Dinosaurs; configurations of pelvis and hips.
Birds;
•Scales of group of a dinosaur which became feathers and descended into birds.
•Birds produce eggs and are also endotherms which is maintaining body temperature.
• The wings came from modified fore limbs with feathers extended outward.
•Has four chamber heart.
Sinosauropteryx prima
Confuciusornis sanctus
Mammals
•
•
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Have hair or fur that were
modifications of scales.
Have four different types of teeth
(incisors) in order tear and rip.
Having this allows them to eat a
variety of foods.
Hominoids/Hominids
•
•
Hominoids; include apes and
humans.
Hominids; human and extinct human
like species.
> due to climate changes it became it
difficult to find food. Most ended up
dying out.
proconsul aficanus
Diversity in mammals
1) *Egg-laying Mammals or Monotremes (platypus)
(2) *Pouched Mammals or Marsupials (opossums,
kangaroos)
Metatheria)
(3) *Placental mammals ( manatee)
Australopiths
Genus Homo
•
•
•
•
• Fossil teeth indcated huimans
ate hard shelled nuts,seeds,and
leaves.
• Close relatives are chimpanzees
and bonobos.
• They did the same as hominids
did.
Were very petite
Narrow jaw
Small teeth
Ancestral to modern humans.
australopithecus africanus