The first amber caridean shrimp from Mexico reveals the ancient adaptation of the Palaemon to the mangrove estuary environment.

The aquatic and semiaquatic invertebrates in fossiliferous amber have been reported, including taxa in a wide range of the subphylum Crustacea of Arthropoda. However, no caridean shrimp has been discovered so far in the world. The shrimp Palaemon aestuarius sp. nov. (Palaemonidae) preserved in amber from Chiapas, Mexico during Early Miocene (ca. 22.8 Ma) represents the first and the oldest amber caridean species. This finding suggests that the genus Palaemon has occupied Mexico at least since Early Miocene. In addition, the coexistence of the shrimp, a beetle larva, and a piece of residual leaf in the same amber supports the previous explanations for the Mexican amber depositional environment, in the tide-influenced mangrove estuary region.