A mysterious creature that washed up on the shoreline of Luis Siret Beach in Villaricos, Spain on Thursday has left beach personnel baffled.

The 13-feet-long decomposing creature is being called a sea monster and sea dinosaur, but its true identity is yet to be ascertained.

Pictures of the unidentified creature have since gone viral on social networking site Facebook, as soon as it was uploaded by local news web sites.

"It's hard to know what we're dealing with. It's very decomposed and we cannot identify what it is", Marina-Sea Life Defense Program, or PROMAR, spokesman Paco Toledano told ideal.es.

"Perhaps we could learn something more from the bones, but to be precise, it would be necessary to perform a genetic analysis, which is very expensive and who would pay for it?" Toledano added.

The mystery mammal was spotted by a woman who had been swimming on the beach. She first found the head on the shoreline while the rest of its body was later found after a search.

"A lady found one part and we helped her retrieve the rest," Maria Sanches of Civil Protection in Cuevas said via GrindTV.com. "We have no idea what it was. It really stank."

"We have submitted the information to colleagues with more experience and knowledge to see if they can tell us something more specific," Toledano said.

The discovery has captured the public's imagination due to the horns found on its head. However, Toledano explained that they are perhaps just bones that fell out of place.

"It's not a longhorn cowfish, that's for sure," he said.

According to the ideal.es report, experts believe the creature is "a fish that lives deep or a shark species".

The creature's decomposing body has now been buried for health reasons but its images are being studied for proper identification.