Here is a detail (see the full illustration on my Science Illustration page) of the JOGGINS (NOVA SCOTIA) CARBONIFEROUS SWAMP FROM 350 MILLION YEARS AGO. The little lizard on the Lepidodendron tree log is Hylonomus lyelli, the earliest lizard and first amniote and thus our and all mammals’ ancestor. This geologic period, the Pennsylvania, had 40% more oxygen than we have now, which made for some extra large insects. The dragonfly pictured (Meganeura) had a wingspan of one meter, and the roach below it was one foot long.
This illustration is for a book entitled Brains Through Time, A Natural History of Vertebrates to be published by Oxford University Press in February 2019. The authors are R. Glenn Northcutt from Scripps Oceanography and Georg Streidter from UC Irvine.