The history of the tortoise

and insects which we see all around

us, other groups that have succeeded out of water include

scorpion

s ,

snail< /p>

s

,crustaceans

such as

woodlice

and land

crab

s,

millipede

s

and

centipede

s,

spider

s and various worms. And we musten

’

t forget the

plants,without whose

prior invasion

of the land none of the other migrations

could have happened.

Moving from water to land

involve

d a major redesign of every aspect of

life,including breathing and

reproduction

.

Nevertheless

,a good number of

thoroughgoing

land animals later turned around,abandoned their

hard-earned

terrestrial

re- tool

ing, and returned to the water have only gone

part way

show us what the

intermediate

s might have been like,on

the way to extreme cases such as whales and

dugong

(including the

small whales we call

dolphin

s )and dugongs,with their

close cousin

s the

manatee

s,ceased to be land creatures altogether and

reverted to

the full

marine habits of their remote don

’

t even come ashore to

do ,however,still breathe air,having never developed anything

equivalent to the

gill

s of their earlier marine

incarnation

.

Turtle

s went back to

the sea a very long time ago and ,like all

vertebrate

returnees to the

water,they breathe air. However ,they are, in one respect ,less fully given

back to the water than whales or dugongs, for turtles still lay their eggs on

beaches .

There is evidence that all modern turtles are

descend

ed from a terrestrial

ancestor which lived before most of the

dinosaur

are two key fossils

called

Proganochelys quenstedti

and

Palaeochersis talampayensis

dating

from early dinosaur times,which appear to be close to the ancestry of all