No fossil animal remains have been found at Fossil Grove itself. However, finds from elsewhere in rocks of the same age show that many creatures lived in and around the coal age forests. Freshwater mussels and fish inhabited the pools and lagoons. Amphibians also lived in these waters and on land. Spiders, scorpions and many different insects thrived in the tropical conditions. There were no bird predators and oxygen levels were high, so insects and other related animals grew very large.
Although the plant remains found at the Fossil Grove are dominated by one species there were many strange and wonderful plants growing in the swamps at that time. Representative plant fossils can be seen in the display cases in the building. Some details about these can be downloaded here:
This part of the Carboniferous is close to the point where reptiles (eventually to become dinosaurs) evolved from the amphibians. The National Museum of Scotland has a good web-article about these early reptiles of the Carboniferous.