Wednesday, August 31, 2011

Orthocerous Fossils

I didn't get a chance to get out yesterday to get any blog photos, so today I'll respond to a request from museum patrons to post information about orthocerous fossils.

The orthoceras mollusk lived in abundance during the Paleozoic Era, between 250 to 750 million years ago. Orthoceras is an extinct member of the class Cephalopoda and is related to the present-day squid and octopus. Numerous tentacles emerging from the larger end of the shell were the most distinct feature of the Orthoceras. The shell was formed as the Orthoceras secreted calcium carbonate from its body and new chambers in the shell were added on as the creature grew.

Found in the Atlas Mountains of Morocco, Orthoceras thrived during the Silurian Period (about 420 million years ago) when the various species evolved into other cephalopods such as the ammonite. The fact that we find their fossilized remains on the border of the Sahara Desert is just one piece of evidence that what is now a desert was once a prehistoric ocean, teeming with strange and unusual life.

The fossils are cut out of limestone deposits.

The bodies of the Orthocerous were long and straight. Like their counterparts the ammonites, these animals had a shell that consisted of distinct chambers that were connected by a tube called a siphuncle, and separated by walls called septa. These chambers were used as ballast in which the animal controlled its balance, which was extremely useful considering they could grow up to 6 feet. They had 8-10 tentacles like their modern-day relatives with an advanced, for their time, nervous system, jaws and eyes. They also had a hyponome, a modified foot shaped like a muscular spout or funnel which they used for locomotion, quickly thrusting out water so they could quickly dart away from predators. They fed mainly on floating plankton, small trilobites and other various gastropods along the ocean floor, or while floating. They could achieve neutral buoyancy by filling up the individual chambers with either gas or fluid though the siphuncle.

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