Over 65 million years ago, during the time of Dinosaurs in the Cretacious Period, bacculites filled the oceans. It was a squid-like animal that preyed upon other sea life in the middle of the ocean current. The shell consisted of a series of camerae, or chambers, that were connected to the animal by a narrow tube called a siphuncle by which buoyancy could be regulated. The chambers are separated by walls called septa. The line where each septum meets the outer shell is called the suture or suture line.
"walking stick rocks"
The suture left behind became beautiful lines and show where the growth plates that the animal added to accommodate its larger size as it grew older. The fossil's spectacular color is caused by nacre and aragonite in the shell material and the refraction of light.