Hippocampus sarmaticus is an extinct species of seahorse, found in 2005 in the coprolitic horizon of the Tunjice hills Lagerstätte in Slovenia, along with the related Hippocampus slovenicus. The horizon dates 13 million years back to the lower Sarmatian during the middle Miocene period, making the two species the earlier known seahorse fossils in the world. Among the remains, one adult female specimen is fully preserved, with bony plates and other important macroscopic features. The rest are mostly juvenile specimens and remains of head and backbones of adults.