Ammonites (Arietites bucklandi) Pair of shells,... Lot 41

Ammonites (Arietites bucklandi) Pair of shells, 190 million years old, Germany Fossil 47x33x10 cm Provenance: market (Italy) Conservation status. Surface area: 70%. Conservation status. Support: 80% (gaps, fractures, additions and restorations, also on verso) Ammonites were cephalopods - mollusks characterized by bilateral body symmetry divided between head and tentacles - with a spiral shell. They are closely related to the living coleoids, i.e., octopus, squid and cuttlefish, although in appearance they are more reminiscent of Nautilus. The first ammonites-more properly ammonoid-appeared during the Devonian (419.2-358.9 million years ago). The last species disappeared during or soon after the Cretaceous-Paleogene extinction event, also called K-T extinction (about 66 million years ago), in which three-fourths of animal and plant species disappeared and among other things all non-winged dinosaurs and most quadrupeds weighing more than 25 kg. Ammonites are excellent index fossils, and it is often possible to link the rock layer in which a particular species or genus is found to specific geological periods. Their fossil shells usually take the form of planispirals, although some helical and non-spiral spiral forms, so-called heteromorphic ammonites, have been found. The name "ammonites," was invented by Pliny the Elder, who noted their similarity to ram's horns (he coined the term "Ammonis cornua," "horns of Ammon," because the Egyptian god Ammon was typically depicted with ram's horns). Ammonites are distinguished by their septa, the partitions that separate the chambers of the phragmocone, by the nature of the sutures at the point where the septa join the outer shell wall, and generally by the siphon. Arietites is a genus of massive, giant psilocerataceous ammonites of the family Arietitidae, in which spirals-squared and transversely ribbed, separated by deep scaling-run along the belly. The fossils are known worldwide from the Lower Sinemurian stage of the Lower Jurassic. The fossils on auction, which date to the Lower Jurassic, belong to the bucklandi species identified by George Brettingham Sowerby in 1816.