Both mammals and dinosaurs are represented. There is a huge (almost endless) variety of species that can evolve via DNA chains, and the random tile map board setup is constantly changing due to certain random events (e.g., Erosion, Greenhouse and icehouse Earth, and Milankovich cycles), Catastrophes (e.g., an Impact event or a solar flare), and the addition of new Biome tiles during play.
This describes a dynamic ecosystem where evolution, environmental changes, and game mechanics interact.  The presence of mammals and dinosaurs highlights the diversity of life within this system. The changing tile map reflects the unpredictable nature of the environment.