Between 500 and 1450 a rivarly developed between the christian european states and

1. glaciers are melting

2. more water going into ocean (water's such as fresh waters, etc)

the cladogram shown here shows similarities and differences among several classes of vertebrates. anatomically, the four have limb structure as their common ancestor. we might separate the mammals from the other three classes because they a) divergent; do not lay eggs b) identical; are warm-blooded c) varied; a four chambered heart d) homologous; have mammary glands