Survivors: Massive Extinction

Along this entire path strewn with massive extinctions, there have, however, been great survivors, families, genii and species that have continued their slow evolution, overcoming the major crises in the course of millions of years, either because their habitats have remained stable or because their evolutionary designs have enabled them to adapt to the changes.

The estuarine crocodile, a survivor from the Cretaceous era.
The first ancestors of the modern crocodiles appeared at the start of the Triassic era, approximately 230 million years ago, in a world dominated by the dinosaurs. They were new evolutionary prototypes that would prove so efficient and adaptable that they would survive to this very day.
The great changes wrought by the massive extinction of the Cretaceous era brought an end to the dinosaurs; but the crocodiles nonetheless managed to survive. Today, their world is very different from that of 80 million years ago, but the same adaptations, the same designs that were useful then continue to serve them in this world of the 21st century.
Large scales protect the crocodile’s body like armour plating. 
Their organs, their senses, their physiology in general is primitive, perhaps archaic, but it has kept them alive for millions of years.
The first crocodilians were land carnivores. They had longer legs than their present-day descendents, adapted to hunting on land, but their bodies were already very similar to those of modern crocodiles. Subsequently, they progressively adapted to an amphibian lifestyle, achieving physical variations on the basic model - the typical body of the crocodiles, which they still successfully use today, and which makes them formidable predators.

The designs that survived the great extinctions, such as the crocodiles, are, in any case, the exception to the rule. Because our world behaves like a living being constantly renewing itself, and that means new species to take over where others left off.
The Earth is now a world of sophisticated specialists.

 Biological communities are composed of thousands of species, millions of living beings that base their lives on others, in such a way that they all depend on each other.
This sloth of the Amazon jungle is capable of surviving in a world of hunters as efficient and specialised as the jaguars. And it has managed to do so thanks to something as apparently simple but in practice incredibly difficult to achieve as being able to live without ever needing to go down onto the ground.
The canopy of the jungle is the safest place for creatures as slow as the sloth. Up here, they find food and have managed to drink from the leaves and trunks in which the rainwater collects. In addition, their adaptations to arboreal life have led them to develop a disguise based on slow movements and greenish algae which tinge their brown hair. In exchange for such radical physiological changes, the sloths cannot flee if an enemy detects them and must always live near the cecropias on which they feed. They are therefore entirely dependent on the survival of these trees and, in general, the Amazon jungle.
Such specialised unions as that of the sloths, the bluish-green algae that live in their hair and certain species of Amazon trees such as the cecropias have worked so well that they have spread around the entire world. And this has brought unprecedented richness to the biodiversity of the Earth. 

Ecological unions have led life to diversify as never before in its long evolutionary history. But this success has its risks. 
Now more than ever we understand that each animal, each plant, each environmental factor, can influence the lives of all the other members of a given ecosystem. 
In the same way as some sociable species have managed to conquer an enormous variety of environments thanks to the specialisations of the individuals of the group in the different tasks required by society, so these complex ecosystems need the different members that comprise them in order to function correctly. 

Seen in this way, the ecosystems, and the planet as a whole, behave like independent living organisms that depend on the work of each and every one of their cells, tissues, organs and organic systems. They are all important and, above a certain number, they are all vital.
This specialisation was taken to extremes in the islands which the continental drift separated from all other landmasses.
Madagascar was one of them.