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Location Mean atmospheric O2 Mean temperature |
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Geologic Time Scale
Era: Paleozoic |
Ichthyostega portraitClose-up of a three-foot-long tetrapod of the genus Ichthyostega 365 million years ago in what is today the Canadian Arctic. Flanking the Ichthyostega are Rhacophyton ceratangium, a species of unclassified ancient shrub that are thought to be one of the earliest ferns. The reddish fruit-like nodules attached to the fronds on the right are sporangia, enclosures in which spores are formed. The large tree-like trunk on the far left is the base of a young Archaeopteris. In the foreground are prehistoric arthropods--a millipede on the left and on the right "roachoids" on trunk of a decaying Lycopsid. Arthropods had been walking the Earth for 40 million years before vertebrates like Ichthyostega began venturing ashore. Ichthyostega was one of the earliest tetrapods, a descendent of lobe-finned fishes and ancestor of amphibians. Ichthyostega had lungs and seven-toed limbs that allowed it to move about the shallow waters and shores of swamps and floodplains. It was among the first terrestrial vertebrates. |