Sub Species & Unique flora and fauna

Scientists say that the Galapagos flora and fauna are unique due to the climate, envirnoment elements such as humidity, atmospheric pressure, gravity at the poles, isolation, temperature, rainfall etc... but i on the contrary feel, it is because of isolation alone, these is prehistoric creatures like the crocodile or the cockroach.
Tasmanian Tiger 


The creatures below looked like photoshop work initially, but then there is enough written about these in search engines like google too
This site above is a very good link
lamas are camels ancestors
Elepants ancestor
there are 5500 different species of frogs in the world, the biggest one is the bull frog in Africa and the smallest one is 1 centimeter, in madagascar.