Tag Archives: invertibrate

Geopic of the week: Conical Nautiloid



Above is the fossil remains of a marine organism called a conical nautiloid.  These were common in the shallow sea that covered Arkansas during much of the Paleozoic era 540 to 250 million years ago.  This one was collected from shale of the Pitkin Formation in pieces over a period of years as it weathered slowly out of the outcrop.

Conical nautiloids are extinct now, but they are the evolutionary forerunner of the sleeker, more deft coiled nautiloids that thrive in the ocean today.  They were marine predators, akin to squid, except that they had a shell.  They used their shells for protection, buoyancy, and as a means of propelling themselves through the water by squeezing a stream of water out of the empty chambers like a jet.

It’s common to find conical nautiloid fossils that are smaller than a pinky finger; however, some have been unearthed in Arkansas that were as long as 8 feet.

Geopic of the week: Fossiliferous limestone


This is a picture of weathered fossiliferous limestone of the Pitkin Formation.  It was taken in a quarry near Batesville Arkansas.  The picture displays fossil remains of two common aquatic animals that lived in the shallow sea covering northern Arkansas between 360 – 320 million years ago. 

The screw-shaped remains are parts of bryzoans; they are commonly referred to as Archimedes screws.  The nut-shaped fossils- which also resemble rolls of smarties candies- are the remains of crinoids, commonly called sea-lilies, which have living relatives in the ocean today.  Both animals lived by attaching themselves to the sea floor and filtering food, such as plankton, from the ocean water.