GASTROPOD FOSSIL

Gastropods evolved early in the Cambrian, roughly 525 million years ago, but since the Paleogene have become the most common of mollusks, inhabiting most aquatic and terrestrial environments. They have a muscular foot, eyes, tentacles and a special rasp-like feeding organ (called the radula) that is composed of many tiny teeth. The class is made up of the snails, which have a coiled or conical shell into which the animal can generally withdraw; and also, the slugs, which are snails whose shells have been reduced to an internal fragment or completely lost in their long and fruitful course of evolution. There are currently 721 families of gastropods known, of which 245 are extinct and appear only within the fossil record. Of the 245 extinct families of gastropod is an estimated 15,000 or more individual species. Due to the fact that these marine and land dwelling mollusks have been multiplying on Earth for roughly 525 million years, their fossil remains are commonly found. Typically, fossilization begins with remineralization of the calcium carbonate shell and it is replaced with more durable variations of silica, such as chalcedony, over lengthy periods of time.

Gastropods were first described as "gasteropodes" by Georges Cuvier, the French nationalist and zoologist, in the year 1795. The word itself comes from Greek gastḗr for 'stomach', and poús for 'foot', which is in reference to the fact that the animal's "foot" is positioned below its bowels.