Dendraster gibbsi
Late Pliocene
Etchegoin Formation
Kings County, CA, USA

Bitten echinoid. Average size 1.5 inches.

Pathology. Pathologic. Predation

Dendraster is a genus of sand dollar (an echinoderm group) that appeared late in the Miocene and still lives today.  The species, D. gibbsi, is common at some Pliocene localities in California. 

Occasionally, unusually large specimens or those showing healed injuries, like this one, are found.  They exhibit highly-irregular outlines but with the edges unbroken. Something tried to eat it but was interrupted (perhaps by an incoming wave) and the sand dollar survived the attack and was able to heal up.