| | |
A | Permian,.........|.........|...........|......
R | | | |
Y | Carboniferous,...|.........|...........|......
| | |
P | | | |
R | Devonian,........|.........|...........|......
I | | | |
M | Silurian,.....Polyps. Acalephs. Echinoderms...
A |
R | Azoic.
Y |

MOLLUSKS.
Acephala. Gasteropoda. Cephalopoda.
T | Present,.........|.........|...........|......
E | | | |
R | Pliocene,........|.........|...........|......
T | | | |
I | Miocene,.........|.........|...........|......
A | | | |
R | Eocene,..........|.........|...........|......
Y | | | |
| | |
S | Cretaceous,......|.........|...........|......
E | | | |
C | Jurassic,........|.........|...........|......
O | | | |
N | Triassic,........|.........|...........|......
D | | | |
A | Permian,.........|.........|...........|......
R | | | |
Y | Carboniferous,...|.........|...........|......
| | |
P | | | |
R | Devonian,........|.........|...........|......
I | | | |
M | Silurian,.....Acephala. Gasteropoda. Cephalopoda.
A |
R | Azoic.
Y |

ARTICULATES.
Worms. Crustacea. Insects.
T | Present,.........|.........|...........|......
E | | | |
R | Pliocene,........|.........|...........|......
T | | | |
I | Miocene,.........|.........|...........|......
A | | | |
R | Eocene,..........|.........|...........|......
Y | | | |
| | |
S | Cretaceous,......|.........|...........|......
E |