Fossil of Trilobites:
 
Mediums measure approx. 89 x 50 mm: thickness of 25 mm: weight is approx. 136 grams.
Smalls meaure approx. 77 x 40 mm: thickness is 19 mm: weight is approx. 71 grams. 
 
Trilobites marine arthropods that first appeared around 521 million years ago, shortly after the beginning of the Cambrian period. They died out at the end of the Permian, 251 million years ago. They are found all over the world.