Micraster Fossil Flat Sea Urchin Prehistoric Echinoderma Cretaceous Collection (2)

Fossil Sea Urchin Micraster (Spatangus) decipiens mm 37 x 36 x 23 gr 32.4 Invertebratas Echinoderma Echinozoa Echinoidea Irregular Flat Marine Urchins Prehistoric Extinct Mesozoic Cretaceous Collecting Paleontology Museum.

Pleasant fossil find of Sea Urchin Irregularia Spatangoida from the late Cretaceous, representative silicified collectible specimen of good quality and in a fair state of conservation, with evident and appreciable details of the shape of the rounded exoskeleton and the five-shaped petal symmetry.
Only a piece, as in photo.

Micraster is an extinct genus of Irregular Sea Urchins of the family Micrasteridae from the late Cretaceous (94.3 million years) to early Eocene (55.8 million years). Its remains have been found in Africa, Antarctica, Europe and North America.
Micraster was a benthic echinoid that lived in a burrow beneath the surface of the sediment. The exoskeleton is clearly bilaterally symmetrical and has a deep anterior groove to absorb water containing organic particles and conduct them to the mouth. It's a fairly large species. The rather swollen upper face is wide at the back with a keel. The apex is eccentric anteriorly.
Micraster is cited as a typical example of a fossil whose continuous evolution can be traced for approximately 10 million years through Late Cretaceous chalk deposits. Micraster fossils are so abundant that it is possible to collect hundreds of thousands of them and trace their gradual evolution. The changes are seemingly trivial. There is a slow alteration in shape from rather flattened to rather arched, along with an increase in length. The mouth constantly migrates forward, its distance from the anterior edge of the lower surface decreasing from about one-third of the length of the body in the early types to one-sixth in the latter, over a total length of fifty to sixty millimeters. Even if the changes involved are small, they are absolutely continuous, clearly showing how evolution works.