Syngnathus avus
Middle Miocene
Monterey Formation
Santa Maria, California, USA

Huge, extraordinary 5 foot x 2+ foot display slab with at least 23 fish

Syngnathus is a genus of pipefish best known as a fossil from Oligocene to Pliocene localities in Europe though S. avus was named based on specimens found in rocks of the Los Angeles Basin just over 100 years ago. Pipefishes live today in tropical to temperate waters of the Pacific, Atlantic, and Indian Oceans, usually in seagrass beds. They belong to the same family as seahorses, the Syngnathidae.

See this paper (PDF) for an overview of the evolution of the Syngnathidae: The evolutionary origins of Syngnathidae: pipefishes and seahorses