1. be able to name and describe the four synapomorphic characters of chordates
2. for each of the clades of chordates (cephalochordates through mammals and everything in between) be able to name their diagnostic characteristics (e. g., chondrichthyes have placoid scales and a cartilaginous skeleton)

1.

1 presence of notocorde at some stage of ontogenetic development. This notocorde is located dorsal to the digestive tract, it is a structure that gives rigidity to the body and in some clades it is replaced by the spine.

2. presence of the posttanal tail at some stage of development

3. Presence of complete digestive system with mouth and anus

4.  Hollow, tubular and dorsal nerve cord, in complex animals, the brain and spinal cord develop from this structure

2. Cephalochordata: The notocord extends to the tip of the anterior area, the gonads are segmented, They have small size. they are transparent, laterally compressed, and sharp at both ends .

Urochordata:   the wall of the body has a tunic consisting of a cellulosic substance called tunicin; the larvae have notochord in the caudal region

Vertebrata: They have a skull that protects the brain. they have a backbone that supports the body.

Chondrichthyes: cartilage skeleton

Actinopterygii:  fish with radiated fins

Sarcopterygii: lobed-finned fish

Amphibia:  they have metamorphosis

Reptilia:  epidermal keratin scales.

Birds:  forelimbs turned into wings, body covered with feathers

Mammals:presence of milk-producing mammary glands for offspring

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what is a measurement of the earth’s history divided into time periods?

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sedimentary rock

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radioactive elements