Is This a Giant Seahorse Fossil?
Alex Kasp, Snopes, September 15, 2017
http://www.snopes.com/giant-fossil-seahorse/
http://www.snopes.com/category/facts/photos/
Also, it seems implausible that a person would
find such a fossils on a corestone.
A paper about real fossil seahorse can found in:
Teske, P.R. and Beheregaray, L.B., 2009. Evolution
of seahorses' upright posture was linked to
Oligocene expansion of seagrass habitats. Biology
letters, p.rsbl20090152. (Open Access)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781918/
Yours,
Paul H.