The creepy thrift store find was dark in color, with one plastic eye and long teeth.
The surprising discovery shocked an employee who found it late Tuesday at the Goodwill store in Goodyear, AZ.
The donation is suspected to have been dropped off over the weekend and did not make it to the floor to sell.
The Goodyear Police Department were called to the store after it was found and took what looked like a human skull to the medical examiner's office.
The creepy thrift store find was dark in color, with one plastic eye and long teeth.
Frequent shoppers at the Arizona Goodwill were stunned to find out what was donated and told Fox 10: 'That's creepy. That's crazy. We come here all the time.'
They added: 'So many questions I think need to be asked.'
A spokesperson for Goodwill of Central and Northern Arizona said that the staff followed the appropriate protocol as they contacted local authorities right away.
After being dropped off at Maricopa County Office of the Medical Examiner, it was determined that the skull is believed to be of 'historic origin'.
After preliminary review, officials saw no forensic significance with the skull.
Lisa Berry, a spokesperson for Goodyear Police Department said: 'Goodwill did do the right thing. Anything suspicious should always be reported.'
The skull has no 'forensic significance, meaning there appears to be no associated crime,' said Berry.
Berry added: 'It did not ever make it to the floor. It was in the donation box, again, with other taxidermy items.'
The person that donated the skull is unknown, but they did drop it off along with taxidermy items.
Another customer heard the news and said: 'I've never found anything remotely close to that, that's really scary.'
Though officials think the skull is not involved in any criminal case, an investigation is underway to look further.
Goodyear Police think the investigation could take weeks and even months to get to the bottom of this jaw dropping mystery.
According to Arizona Republic it was unclear if the skull will be returned to the store and if so, what the price will be.
Being a "journalist" is not funny, I guess.