Ichthyostega
So, although not well adapted for walking on land, this small animal could walk. It may have been one of the first vertebrate animals to walk on land. The sea scorpions were probably the first animals to walk on land many millions of years earlier. If you look closely at the drawing you can see the gills. The gills are above the front leg and slightly forward of that leg. Ichthyostega had gills like a fish but a head like an amphibian. It had a fin on the tail but legs for walking. Of course its legs could also be used for swimming. It is considered a transitional species in the evolution of vertebrates. This drawing shows a very low tide where some of the reef life is now above the water line. This could be a sand bar or on a beach in an estuary where fresh water meets the sea. Ichthyostega lived in the Late Devonian and was one of the first tetrapods. Tetrapod means 4 legs.
The below photo is from the awesome Wyoming Dinosaur Center in Thermopolis Wyoming.
Ichthyostega model
This first sea scorpions lived millions of years before the Ichthyostega. The few plants on land that I drew evolved in the Ordovician Period. This drawing is set in the Silurian or Ordovician or Devonian Periods because sea scorpions and placoderms lived in all those periods. The placoderm is the fish that is under attack by the sea scorpion. Placoderms were early fish with armored heads. Note that the sea scorpion is on a rock. . . AKA on land. The sea scorpions had curtain lungs and could passively breathe oxygen from the air. They also had gills so they probably spent most of their time in the ocean.
Sea Scorpion catching a Placoderm
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