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Amniotes

I am studying Amniota and I was wondering if someone could explain to me the following concepts. I know that the features of Chordata are the notochord, dorsal nerve cords, gill clefts (except for Tunicata); segmented muscles and a post-anal tail. I know that developmentally we are related to echinoderms. Can you explain the relationship between the Cordata and Echinodermata? Using the bird, reptile and mammal (or those that came from an aminotic egg) as an example can you explain the following:
a) Why these 3 (bird, reptile and mammal) are grouped together?
b) What advantages (from an evolution perspective) do these three (as representatives of chordata) have over echinoderms?
c) How the above advantages suit a certain environment or habitat?

Also can you some websites that might be helpful in understanding this concept.

Solution Preview

You have all the important features of chordates listed. The key one is that they have a notochord at some point in their development. Another feature is that they have a bilateral body plan. This means that they have a left and right side that are not identical. Echinodermata consist of star fish, sea urchines etc. The main difference is that echinoderms have radial symmetry (specifically pentaradial meaning 5 sides) that are identical. Echinoderms like chordates are deuterostomes (anus forms first; http://tolweb.org/Deuterostomia/2466). They ...

Solution Summary

Examination with web references of the differences between the different groups of amniotes and the advantages they have over echinoderms. cavities.

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