For your consideration is this collection of authentic North American Trilobites from the Utah area and polished pairs of Ammonites set in a glass and wood display case. Trilobites, exclusively marine animals, first appeared at the beginning of the Cambrian Period, about 542 million years ago, when they dominated the seas. Although they became less abundant in succeeding geologic periods, a few forms persisted into the Permian Period, which ended about 251 million years ago. Ammonites were marine animals belonging to the phylum Mollusca and the class Cephalopoda. They had a coiled external shell similar to that of the modern nautilus. In other living cephalopods, e.g. octopus, squid and cuttlefish, the shells are small and internal, or absent. The ammonites became extinct at the end of the Cretaceous, around 66 million years ago, at roughly the same time as the dinosaurs disappeared. The ammonites sit on the left side of the case in pairs. They show colors of brown, grey, black and yellow with one side being highly polished and smoothed showing the great detail of the ammonite shell. There are 22 pairs present in the case. The Utah Trilobites sit on the right side of the case and show grey and black colors. They show great detail in the exoskeletons. The largest ammonite measures 1 3/8" L x 1 1/16" W, while the largest trilobite measures 1 13/16" L x 1 1/8" W. The case measures 12 1/2" L x 18" W x 2 1/8" H.