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29.2 The Vertebrates
New characteristics of the common ancestor of each group are noted for each branch of the tree.
The first vertebrates appeared in the geologic era.
The nonvertebrate chordates have certain features that differentiate them from the tyke tyke tyke tyke tyke tyke tyke.
The four chordate characteristics are found in embryos.
The notochord is usually replaced by a column of individual vertebrae.
The intervertebral discs are made from the remnants of the notochord.
The part of the body that is flexible but strong is called the vertebral column.
The neural tube is surrounded by the vertebrae during development.
The flexible column protects the nerve cord.
The brain has increased in complexity and specialized regions have been developed to carry out specific functions.
Complex sense organs accompany the high degree of cephalization.
The eyes grow out of the brain.
The ears are mostly equilibrium devices in aquatic animals, but they also function as sound-wave receivers in land animals.
The skeleton of the animal is a living tissue.
It serves as a place of attachment for muscles and protects internal organs.
The skeleton and muscles form a system that allows rapid and efficient movement.
There are two pairs of appendages.
Terrestrial tetrapods have four limbs, while fishes have two.
There is a large coelom and a complete digestive tract.
The blood in animals is contained within the vessels of the body.
The respiratory system is made up of lungs and gills.
The body of water is regulated by the kidneys, which are important excretory and water-regulating organs.
Sex differences and reproduction are usually sexual.
The Paleozoic era is distinguished by the emergence of the first animals.
The start of the Cambrian period saw a sudden appearance of Chordates.
Both jawless and jawed fishes appeared by the end of the Ordovician period.
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