Pictured here is not an alligator or lizard skin fossil, for which these are commonly mistaken. It’s an impression of the trunk of a now extinct tree-sized plant, known as a Lepidodendron. It was collected from a stream bed in north Arkansas. The diamond-shaped patterns are sockets where leaves once attached to the trunk. The holes that are just visible within the “diamonds”, are pores through which the plant inhaled carbon dioxide.
Lepidodendron were common in Arkansas during the Carboniferous period (359-299 million years ago). The Carboniferous (or coal-bearing) period is known for lush vegetation. Many of the earth’s important coal deposits were formed from the remains of the rich forests that dominated the land during that time.
Above is a commonly misunderstood geologic feature called an Asterosoma. Almost everyone, upon first seeing an Asterosoma, thinks it’s either a fossilized plant, flower, or some kind of fossilized animal – usually an octopus.
Asterosomas are actually trace fossils left behind by ancient marine animals (most likely worms or shrimp) that burrowed through mud in a delta or tidal-flat. This one was found in the Carboniferous section of north Arkansas and is roughly 300 million years old. These trace fossils are called Asterosoma because of their star-like shape.
In cross-sectional view, multiple Asterosomas sometimes overlie one another connected by a central vertical tube – like a garland of Asterosomas. This suggests that, as new sediment was periodically washed into the environment, the animal may have burrowed its way back to the top of the mud and wallowed out another home for itself. The animal itself was too soft-bodied to be preserved in the rock record.