worked Cleoniceras - Fossilised animal - cleoniceras besaiei - 20.5

Cleoniceras besaiei is an extinct species of ammonite, a marine cephalopod that lived during the Cretaceous period, about 100 million years ago. This fossil is particularly valued for its beauty, especially when it preserves the mother-of-pearl and the intricate sutural lines clearly visible. The shell of Cleoniceras besaiei is generally of subcircular or elliptical shape, with a cross-section that can be slightly compressed. The spiral of the shell follows a continuous and regular curve. Specimens can vary greatly in size, but the shell is usually of moderate size compared with other ammonites, with a diameter that can reach a few centimeters. The mother-of-pearl of Cleoniceras besaiei, if well preserved, is bright and iridescent, showing reflections ranging from green to blue and purple. This inner layer is composed of aragonite, a form of calcium carbonate that gives the shell a special luster and the characteristic iridescence. An extremely important group from a paleontological point of view belonging to the Devonian-Cretaceous period. Totally extinct by the end of the Cretaceous, it is thought to derive from ancestors belonging to the Nautiloidea. Although part of the mollusk cephalopod group, the ammonite is distinguished especially by the shape of the shell characterized by bilateral symmetry. The shell divides into a single anterior region where the animal resided and a posterior region divided into chambers. The line marking a closure between the chambers is very indicative and facilitates the recognition of the species. Moreover, its contour, in the early forms rather simple and linear, has gradually evolved to the most recent ammonites where it is often very rugged and almost baroque. Sizes vary: from a few cm up to about 10 cm. Being a totally extinct marine species, one can only hypothesize their lifestyle. It is believed that forms with smooth exterior shells were swimming predators. Species with more ribbed and ornamented shells were predominantly benthic. A fascinating lot. This Cleoniceras after undergoing the first polishing operation is subjected to a processing that gives it ribs that highlight its size. Finally it is polished again. Display stand not included. Happy bidding.

估價:$616.12

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