Category Archives: Trace Fossils

Geo-pic of the week: Trilobite Romance

trilobite meeting in pennsylvanian

The photo above shows trace fossils that record the travels of two trilobites.  Trilobites are an extinct group of marine invertebrate animals, resembling horse-shoe crabs, that flourished for 100s of millions of years in the Paleozoic Era (540-250 mya).   The tracks the animal left are known as the trace fossil, Cruziana.  It appears that one traveled from the right side of the photo, the other from the left, until they met in the middle where they rested for a while.  At the center of the photo are resting traces known as Rusophycus.  Perhaps they became friends or maybe they were even more than friends?  It is Valentine’s Day.  Their traces are preserved in the Atoka Formation of west-central Arkansas.  

Geopic of the week: Skolithos

 

st. pete skolithos

Skolithos is a common type of trace fossil that has been found in rocks as old as 541 million years.  Trace fossils are not the fossilized remains of organisms but rather the burrows, footprints, and other structures that resulted from the animal’s activities.

In the case of skolithos, it’s widely believed that a vermiform (resembling a worm) animal created the straight, vertical, tube structures.  These worm-like critters probably lived by filtering plankton from the turbulent water of a shallow marine environment.  The vertical tubes may have been a dwelling place to retreat to, though their specific purpose is not known.

In the above picture, captured in north central Arkansas, a sandstone has weathered to reveal skolithos traces permeating the approximately 460 million year old rock.  This example is from an exposure of the St. Peter Formation, Buffalo National River Park, Marion County, Arkansas.

To see more views of skolithos traces from Arkansas click here

Geo-pic of the week: Conostichus trace fossils

Conostichus topConostichus bottom

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.