Orthoceras: Grew Feet Out of its Head
In Iowa, United States
Size:  (not chosen)
How Geocaching Works
The coordinates will take you to a roadcut near Graf, IA. Many fossil laden rock samples can be found on the ground if you are unable to climb to the fossil layer.
This EarthCache will take you to a roadcut, less than one quarter mile out of Graf, IA. This roadcut has exposed Ordovician bedrock over 400 million years ago. This roadside cut stretches for approximately ½ mile with numerous access points. Parking is on the roadside. Please use caution and watch for traffic. You are allowed to retrieve fossil specimens, but NO DIGGING is permitted.
During the Ordovician Period, the surface of the earth was quite different than it is today. 400 million years ago, nearly all life on earth was in the oceans. The only land life was in the form of primitive plants near the water line of the coasts, probably mosses and algae. Insects did not yet exist, nor did amphibians or reptiles. Fish as we know them did not exist, although a form of primitive fish began to appear by the end of the Ordovician. Though Ordovician life sounds primitive by today's standards, the life during this period was more advanced than life in the earlier Cambrian Period. Ordovician life was characterized by a dramatic increase of the shelly fauna, corals, and bryozoans. The shelly fauna include the brachiopods which did exist prior to the Ordovician, but were less numerous and mostly unarticulated. The Ordovician introduced numerous articulate brachiopods which have a tooth-and-socket arrangement along their hinge line.
This particular site demonstrates a prolific bed of beautifully preserved Orthoceras.
Orthoceras was an ancient mollusk that lived more than 400 million years ago. The name means straight horn, referring to the characteristic long, straight, conical shell. The preserved shell is all that remains of this ancestor of our modern-day squid.
The soft body lived in the last open-ended segment at the large end of the conical shell. As the body grew and the housing segment became too small, a dividing wall, called the septa, grew to separate the old “home chamber” from the new one. The differences in the composition of these shell parts allowed for differences in fossilization so the parts can be seen.
The siphuncle is a tube that runs the entire length of the shell, through each of the chambers. This tube had two functions. Once filled with water, the nautiloid could force the water out, propelling itself backward with a kind of jet propulsion. By releasing the water and leaving air space, the tube could serve as a bouyancy device allowing the animal to rise and lower itself to different depths.
These straight shelled nautiloids ranged in size from less than a centimeter to more than 14 feet long!
All the living relatives of these nautiloids, squid, octopus, cuttlefish, and nautilus are predators, and we can assume that orthoceras was also a hunter of the Paleozoic seas, possibly having trilobites for breakfast!
Notice the siphuncle and septa in the fossil below. The siphuncle is the line running down the center from head to tail. The septa are the short curved lines that run across or side to side.
To log this EarthCache, you must:
• Search the site and find at least one Orthoceras specimen.
• Post a photo of the fossil and the elevation you found the fossil
• Please e-mail the averaged dimension of the Orthoceras you found
• Please post a photo of yourself at this fossil site
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Last Updated: on 5/19/2013 7:36:48 PM Pacific Daylight Time (2:36 AM GMT)
Coordinates are in the WGS84 datum