List two important groups of organisms that appeared during each of the three most recent geologic eras.

The three most recent geologic era include Cenozoic (also known as the age of mammals), Mesozoic (also called the age of reptiles), and Paleozoic, with Cenozoic being the current era. All these eras are a part of the Phanerozoic eon and each is further divided into periods, for example, the Cenozoic era is divided into the Tertiary and Quarternary periods.
The Paleozoic era lasted from 251-542 million years ago, while the Mesozoic era lasted from 65-251 million years ago. The Cenozoic era started around 65 million years ago and is currently underway.
The most important groups of organisms that appeared during each of these eras are:
1) Cenozoic: Human beings, rodents
2) Mesozoic: Mammals, birds, flowering plants, primates
3) Paleozoic: Fish, reptiles, amphibians
The Cenozoic era is most famous for the diversity of the mammals and the evolution of human beings. The Mesozoic era is known for the evolution and extinction of the dinosaurs, and evolution of birds, mammals, primates and flowering plants. The Paleozoic era is most famous for the evolution of the fish, chordates (animals with a backbone), vascular plants, amphibians, etc.
Hope this helps.
https://www.aoml.noaa.gov/outreach/floridaseagrant/pdf_files/TropicalConnections_GeologicalTimeWithMajorEvolutionaryEventsInFossilRecord_KruczynskiFletcher.pdf