Where did McCartney find "My Carnival"?

I'm always thrilled when I discover where the Beatles found inspiration for their songs. And sometimes that inspiration bordered on infringing other's rights: examples are Harrison getting in trouble for My Sweet Lord vs. She So Fine, Lennon angering Chuck Berry's lawyers over Come Together, and McCartney.......
It seems that I don't have an example of McCartney crossing the line when using other people's music; he had some trouble over the the phrase "Ob la di, ob la da", and financially compensated the alleged source. And he clearly paraphrased Chuck Berry's "Back in the USA" in his own "Back in the USSR, but that's about it. McCartney is quite frank about being influenced by a whole range of artists, but - as far as I know - has never been suspected of copying. In fact, McCartney takes great care to avoid accidental copying, as exemplified by his hesitation to release Yesterday: he was afraid that he had heard the melody somewhere.

Some time ago, I heard the song "Hey Little Girl" by Professor Longhair. Professor Longhair blended Afro-Cuban rhythms with rhythm and blues. The most explicit is Longhair's Blues Rhumba,' where he overlays a straightforward blues with a clave rhythm.The piano part for the rumba-boogie "Hey Little Girl" employs the 2-3 clave onbeat/offbeat motif.

This song has nothing to do with Hello Little Girl, the first song known to be written by Lennon. But it did remind me of McCartney's style of songwriting. I felt there could be some influence of Hey Little Girl on Hey Jude (more than just the Hey"...), but could not pinpoint it exactly. And then I heard the song "My Carnival", on McCartney & Wings re-release of Venus & Mars. The music and melody of My Carnival is an exact copy of Hey Little Girl! In the remix in BDJ's Cellar you can confirm that yourself.

Where and how did McCartney pick up this song by the rather obscure Professor Longhair? Henry Roeland "Roy" Byrd (December 19, 1918 – January 30, 1980), better known as Professor Longhair, was a New Orleans
blues singer and pianist. Longhair's first recordings were made at the Hi Hat Club, where a rudimentary recording studio was set up. Four sides were issued on the tiny Star Talent label as by Professor Longhair & His Shuffling Hungarians, including Hey little Girl (1949). He is best known for his song "Mardi Gras in New Orleans", which has the same chords and melody as Hey Little Girl. There is evidence that Mardi Gras was actually performed by McCartney (on MoMac's Hidden Tracks Vol.9 and Complete Cold Cuts). McCartney has never played this song in concert. So where did McCartney hear "Mardi Gras in New Orleans"?

Wings flew to New Orleans to record their fourth album,“Venus and Mars.” And on Mardi Gras Day, Feb. 11,
1975, the McCartneys waded into the holiday revelry, masking as a pair of clowns. McCartney, asked what
musicians he’d heard during his New Orleans 1975 visit, said: “Well, we saw Professor Longhair play. And
he’s the greatest. He’s a classic. I love ’em.”

Wings recorded “My Carnival” at Sea-Saint the day after Mardi Gras. The song’s piano, rhythm and vocals
parallel the music of Professor Longhair's Mardi Gras and Hey Little Girl.

Venus and Mars reached No. 1 internationally. The original album did not include “My Carnival.” Was
McCartney hesitant because he might have copyright issues? Five years after Professor Longhair’s death,
McCartney released “My Carnival” as the B-side of “Spies Like Us,” (title song for a 1985 Chevy Chase-
Dan Aykroyd movie). In 1993, Venus And Mars was remastered and reissued on compact disc as part of "The Paul McCartney Collection" series; My Carnival was released as a Bonus Track.

So there we have it, clear evidence that McCartney copied others; we have to note that he single’s label says: “Recorded in New Orleans & dedicated to Prof. Longhair”. Now there's an understatement!