Dinosaurs, birds and mammals

Birds, reptiles and mammals all share a common 'feature' that indicates their common ancestry. Namely, a membrane surrounding their early offspring.
For this, these groups are known as Amniotes, a clade [group in biology that puts all the species with the same ancestors together].

Why is this interesting? Because it means in those times these animals didn't have to go to water to lay their eggs, allowing them to go into drier environments, further inland.

The earth looked something like this:

Related reading:
https://biologycuratorialtrainee.wordpress.com/2011/03/28/the-dragonfly-hangs-like-a-blue-thread-loosened-from-the-sky/

Sources:
Image of the plates http://www-udc.ig.utexas.edu/external/plates/recons.htm
Front image Fred Moon @ Unsplash