Brett Thomson, 36, who owns Leeds graffiti supplies store Artofficial, made the discovery of a lifetime while exploring the cliffs near Reighton Sands caravan park, between Flamborough and Filey.
He uncovered a walrus skull later dated at 140,000 years old - one of the oldest examples of the species Obodenus rosmarus ever found.
Mr Thomson, from Kirkstall, took the specimen to the Rotunda Museum in Scarborough for advice, and was told that scientists from all over the world were interested in the find. Museum staff also decided to hunt for further bones belonging to the skeleton at the site.
The graffiti artist claims that the museum then told him there were no other fossils at the location - but when he returned to the area, he found more bones and discovered that the skull could be valued at more than Â£70,000. He also claimed that the staff told him that he should have sought permission of the landowners - holiday park operators Haven - before removing the fossil, and that he could not have it back.
He is now facing disappointment as he says the museum have not officially credited him with the discovery, and has warned other amateur fossil hunters to be aware of land ownership regulations in order to avoid fines and legal action.
“Obviously my experience was very disappointing. The skull I found is a once-in-a-lifetime find, and it’s sad that the outcome has been less than satisfactory. But I want to use the experience to help others know their rights when they’re out looking for these things.
“I don’t care about the monetary factor. It’s more the fact that I handed over the find in good faith and then found out about the other legal considerations. I’d advise people to get their ducks in a row and know everything they need to about the area they’re in before they find anything. Hopefully, this will help others have a better outcome than my own experience.
“I feel like I have been utterly swept aside and as the finder of such a key piece, that’s a very bitter pill to swallow. I’m very annoyed at the way that I have been treated by the museum who I don’t feel were honest with me from the start. I deserve to be credited for my find. I think that way I have been treated will discourage others from handing in important finds and drive history underground.”
However, the museum have disputed Mr Thomson's version of events, saying that he was invited on a further site visit and chose not to attend, and that he did not respond when they offered to credit him as the finder of the skull rather than the donor - which legally is landowners Haven, who have now gifted it to the Rotunda.
A statement from Scarborough Museums Trust said:
"The fossilised walrus skull was found in the cliffs at Reighton and brought to Rotunda Museum for identification and advice on its preservation. Legislation states that fossilised specimens of great scientific importance should be deposited with an academic institution for scientific research, so Scarborough Museums Trust became its temporary guardians.
"It was established that the landowners of the site on which the fossil was discovered is Haven. They have made the transfer of the artefact as per legislation, which ensures the rightful preservation and research for this specimen of great scientific value. Haven has therefore been credited as the donors of the fossil.
"We contacted the finder on March 27, 2018 to invite him to join us at Reighton to further explore the site and he emailed a response explaining that he was unable to attend. We continued to keep the finder abreast of all developments. On April 23, 2018 we received an email from the finder stating his desire to sell the skull and asking whether the Museum would be interested in purchasing it. At this point we clarified the legal implications, explaining that it possibly was not his to sell and that legal ownership needed to be ascertained. We then contacted him on July 12, 2018 with further clarification of the legal situation and offered to give him official crediting as the finder of the fossil in the exhibition and public realm. We did not receive a response and, consequently, we have not been able to legally reveal his name in the public realm.
"Throughout this process the Museum has been supported by the Museums Association on all legal and ethical matters and to ensure that we have acted within current guidance in accordance with the Museum Code of Ethics.
"We are incredibly grateful to the finder for the discovery and to Haven for making its legal donation to Scarborough Museums Trust. We would be very happy to credit the finder should he wish to provide us with the necessary permission to be named.
"From a legal perspective the public need to be aware when fossil hunting that ownership of any find lies with the landowner and not necessarily with them. We would like to advise anybody to seek advice from their local museum service on discovering anything they believe may be of historical or scientific significance."