the survivors

not everything disappeared

the extinction at the end of the cretaceous was immense, but not absolute.

many groups disappeared.

others, on the other hand, managed to survive.

this is important because the later world did not arise from nothing.

it arose from the lineages that managed to cross the crisis.

birds were the only dinosaurs that survived.

this means that the extinction did not completely eliminate the dinosaur lineage.

a part of it managed to continue.

modern birds are direct descendants of theropod dinosaurs, and that is why, in evolutionary sense, they are still dinosaurs.

their survival was probably related to several advantages:

mammals already existed before the extinction, but in the mesozoic they were usually small and discreet animals.

many of them survived the crisis.

their reduced size, varied diet and ability to occupy shelters or less demanding niches may have been decisive factors.

after the extinction, these mammals found a world full of empty spaces.

and it was then that their expansion began.

in addition to birds and mammals, other organisms and lineages also survived:

survival did not depend on a single characteristic.

it depended on each group’s ability to withstand an extreme ecological crisis.

there is no single reason that explains all cases.

but there are factors that seem to have been important:

large specialized animals usually suffer more when an ecosystem collapses.

smaller and more versatile organisms, on the other hand, may have more options to resist.

after the extinction, the planet was left full of empty niches.

many of the great mesozoic dominators had disappeared.

that allowed the survivors to begin to expand.

birds continued their evolution. mammals diversified. ecosystems rebuilt themselves little by little.

the later world no longer belonged to the large non-avian dinosaurs.