The mystery surrounding a tiny island where a porpoise was apparently carefully buried in a medieval grave has deepened after the remains of a handless figure were unearthed.

Archaeologists digging at a religious island retreat have been puzzling over the porpoise find for months, and the discovery of the figure, possibly a monk or drowned person, has added to the sense of wonder over what was taking place there half a millennium ago.

Results of tests on the porpoise have recently come back and suggest it was buried on the island of Chapelle Dom Hue, off the west coast of Guernsey, in the 15th century.

While the tests were being done, archaeologists spotted a human toe bone exposed in a cliff edge about 10 metres from the porpoise site. When they went back again, a foot had begun to appear as wind and rain eroded the cliff.

They began to dig and found a near-complete human skeleton. Philip de Jersey, a States of Guernsey archaeologist, said the body could be that of a monk as it was believed the island was used by residents from a nearby monastery seeking solitude.

De Jersey said the body was oriented roughly east to west, suggesting a Christian burial. Copper and bone buttons were found, possibly indicating that the person was probably clothed when buried.

The man was just 5ft and his skull was badly damaged. But the most intriguing detail is the lack of hands. De Jersey said: “He is lacking hands and wrist bones, which is mysterious. There are medical reasons a person could lose their hands such as leprosy but the toes are in such good condition it seems unlikely.”

It is also possible that the body was not formally buried but is that of a drowned person, possibly a sailor, that may have washed up on the island centuries ago and by chance been buried. De Jersey said: “It may be that it was a body that had been floating around and the hands had been nibbled. The feet might have had footwear on and so be protected.”

The bones would be analysed next year to try to find out more about the person – and any possible link to the porpoise, he said.

Quite why the porpoise was buried so carefully on the island is a mystery. The marine creatures were eaten in medieval times but it would have been easier to dispose of the remains in the sea, which is only a few metres from the site.

De Jersey said it was possible that a monk hid the body of the porpoise because he was not supposed to have it, or that the body was placed in the hole in salt to preserve it and had been forgotten.

Another intriguing theory is that the animal had some sort of religious significance to the people who used the island.