Fungi All modern
classes of
fungi have been found in rocks of Pennsylvanian age.
Invertebrates The major forms of life at this time were the arthropods. Arthropods were far larger than modern ones.
Arthropleura, a giant
millipede, was a common sight and the giant
griffinfly Meganeura "flew the skies". It is commonly considered that is because of high oxygen level, however some of those large arthropod records are also known from period with relatively low oxygen, which suggest high oxygen pressure may not have been a primary reason for their gigantism.
Vertebrates Amphibians were diverse and common; some were several meters long as adults. The
collapse of the rainforest ecology in the mid-Pennsylvanian (however, prospered due to specific key adaptations. One of the greatest evolutionary innovations of the Carboniferous was the
amniote egg, which allowed for the further exploitation of the land by certain
tetrapods. These included the earliest
sauropsid reptiles (
Hylonomus), and the earliest known "
pelycosaur"
synapsids (
Archaeothyris). Small lizard-like animals quickly gave rise to many descendants. Amniotes underwent a major evolutionary radiation, in response to the drier climate that followed the rainforest
collapse. For some reason, pelycosaurs were able to reach larger sizes before reptiles could, and this trend continued until the
end of the Permian, during which their
cynodont descendants became smaller and
nocturnal, as the reptilian
archosaurs took over, although
dicynodonts would remain megafaunal until their extinction at the
end of the Triassic. Most pre-rainforest collapse tetrapods remained smaller, probably due to the land being primarily occupied by the gigantic millipedes, scorpions, and flying insects. After the rainforest collapse, the giant arthropods disappeared, allowing amniote tetrapods to achieve larger sizes. ==Subdivisions==