This item is a fossil-bearing stone containing ammonites with even some orthoceras specimens. The fossil ammonites seen in the plates are from the Devonian Period and lived in the ancient seas almost 400 million years ago but died out with the dinosaurs at the end of the Cretaceous Period. Ammonites and goniatites are extinct members of the Cephalopod class. Modern members include nautilus, squid and octopus. They first appeared during the Silurian Period (435 million to 410 million years ago) and were abundant and widespread in the seas of the Jurassic and Cretaceous periods (175 million to 65 million years ago). Ammonites are important index fossils-that is, they often link the rock layer in which they are found to specific geological time periods.

Orthoceras ("straight horn") is a genus of extinct cephalopod. This genus is sometimes called Orthoceratites. Note it is sometimes misspelled as Orthocera or Orthocerus. Fossils are common and have been found on many continents, including the Americas, Africa, Europe, and Asia. They are dated to the lower Ordovician to Triassic ages (500 to 190 million years ago). These are slender, elongate shells with the middle of the body chamber transversely constricted, and a subcentral orthochoanitic siphuncle. The surface is ornamented by a network of fine lirae. Many other very similar species are included under the genus Michelinoceras.