Above are two pictures of a trace fossil, Conostichus, from the Ozark Plateaus region of Arkansas. Like other trace fossils, Conostichus are structures found in sedimentary rock that represent the spot where an animal lived, fed, or travelled. Despite their abundance, especially in rocks of the Carboniferous period (299 to359 million years ago), it’s not certain what kind of animal made Conostichus, because the animal’s body wasn’t preserved.
The upper picture is the top of the Conostichus and shows the hole through which the animal entered or exited the structure. The lower picture is the same Conostichus with the top facing down. As you can see, they taper and come to a rounded point at the base, vaguely resembling a badminton birdie.
At present, the most widely accepted theory for their origin is that Conostichus are burrow traces left by Sea Anemone.
Just wanted to let you know that the Statemap 2014-15 field mapping project has resulted in the publication of three new geologic maps. These are the Parma, Prim, and Greers Ferry quadrangles. Reduced images are posted below. These should be available as .pdfs on our website in the near future. I’ll keep you posted!
Greers Ferry Quadrangle
Also, I would like to thank the many people who helped with data collection in the field this year, without whom this project would have been impossible.
Andy Haner Danny Rains
Angela Chandler Stefanie Domrois
Doug Hanson Ty Johnson
Now it’s off to the Brownsville quad for next year!
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.