Large Fossilised Sheet of Ammonite and Orthoceras Shells


A large stone sheet, featuring a variety of Cephalopods, namely Goniatite Ammonites and Orthoceras shells, which are a genus of Nautiloids. This piece has been cut very neatly revealing the inner chambers, where the fossil displays delicate and subtle hues of cream and grey.

Orthoceras – meaning ‘straight horn’ in Latin – is a genus of extinct nautiloid cephalopods, distinguishable by the narrow, conical shells we see here. This sample also features Goniatite Ammonites, which first appeared around 390 million years ago, in the Mid Devonian period, and became extinct around 250 million years ago, in the late Permian Period. This was during the Permian-Triassic mass extinction event, which is thought to have been caused by Ocean acidification. Other species of ammonite survived this extinction.


Date: Around 350 million years old
Condition: Very fine condition, this item has been cut finely and neatly displaying the shells' inner chambers.


Orthoceras are often confused with the somewhat aesthetically similar Bacultes – they both have long and narrow tubular shells. However, Orthoceras existed much earlier – between 300 and 400 million years ago – than Baculites, which lived between 70 and 100 million years ago, during the late Cretaceous period. The two are in fact quite easily distinguishable, by the suture lines along their shell.  Orthoceras have the straight, simple horizontal lines we see here, whereas Baculites have much more intricate, patterned suture lines.

Any remaining species of ammonites became extinct 66 million years ago, in the Cretaceous-Paleogene extinction event. Although, like Ammonites, Orthoceras are cephalopods, they are actually a genus of the nautiloid family of Cephalopods. Although orthoceras themselves are extinct, some nautiloids still survive today. Nautiloids first appeared 500 million years ago, during the Paleozoic era, and were the main predatory species. Only a few species survive today and inhabit seas around Australia and the Philippines. They are sometimes referred to as “living fossils”, due to the belief that the remaining species are of a similar form to their ancestors.

Weight 18900 g
Dimensions L 66 x W 43 x H 2.5 cm
Time Period

Reference: For a similar item see: Christie's, Auction 5357, Lot 627

You may also like…