Micraster Fossil Sea Urchin mm 38 Cretaceous (4)

Fossil Sea-Urchin silicified Creaceous mm 38 x 38 x 25 - gr 45.9 Micraster decipiens. The Fossil Sea Urchin you will receive is just the one of the Photo.

Micraster is an extinct genus of irregular Sea Urchins from the Late Cretaceous (94.3 million years) to the early Eocene (55.8 million years). His remains have been found in Africa, Antarctica, Europe and North America. Micraster was a benthic echininoid that lived in a den beneath the surface of the sediment. The exoskeleton is clearly bilateral and has a deep front groove to absorb the water containing the organic particles and lead them to the mouth.
Micraster is cited as a typical example of a fossil whose continuous evolution can be traced for about 10 million years through the late Cretaceous gypsum deposits. Its fossil  are so abundant that it is possible to collect hundreds of thousands and trace a gradual evolution. The changes are apparently trivial. There is a slow alteration of the shape from rather flattened to rather arched, together with an increase in length. The mouth constantly insinuates itself forward, its distance from the front edge of the lower surface decreases from about one third of the length of the body in the first types to one sixth in the last, over a total length from fifty to sixty millimeters. Although the changes in question are small, they are absolutely continuous, clearly showing how evolution works.
Phylum: Echinodermata
Class: Echinoidea
Subclass: Euechinoidea
Infraclass: Irregularia
Order: Spatangoida
Genus: Micraster
Agassiz, 1836