The corpse of the 6ft mammal lay partially wrapped in two bin liners among trees on Goring Greensward near the end of Aldsworth Avenue, around 100 metres from the sea.
Herald reader Patrick Heyland called our newsdesk after he made the grim discovery at around 1pm today (Thursday, January).
"It's a most unusual sight," said Mr Heyland. "Someone has obviously brought it up from the shore."
Billy Elliott, from the Worthing and District Animal Rescue Service, said he would contact experts at the Natural History Museum whom he believed would take the porpoise away and conduct a post mortem examination.
"We wouldn't normally expect to see them on this stretch of coast," said Mr Elliott. "We do get them around occasionally but they are few and far between."
Mr Elliott said museum scientists may well compare their findings with the results of an examination on a porpoise which washed up on a Lancing beach in December.
He said: "They might well be interested to compare them to see if symptoms are the same in case there is a problem out at sea such as deep sea trawling or global warming."
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