Led Zeppelin's plagiarism trial over the authorship of "Stairway to Heaven" moved into its fourth day on Friday, with an economist taking the stand and telling jurors that the group has collected almost $60 million over the past five years from its songs.

But the biggest news was the appearance of Zeppelin bassist and keyboardist John Paul Jones, who's not named as a defendant in the case but took the stand for 20 minutes, testifying on his former bandmates' behalf.

Michael Einhorn said that Jimmy Page and Robert Plant, Zeppelin's main songwriters, have collected around $58.5 million for their work, including "Stairway to Heaven," which is at the center of the lawsuit.

Page and Plant are on trial for allegedly ripping off the guitar line that introduces Zeppelin's classic 1971 track "Stairway to Heaven." The estate of the late guitarist Randy California claims that the same music can be heard in his band Spirit's 1968 song "Taurus." Page has repeatedly said he was unfamiliar with the earlier cut, an instrumental, when he wrote "Stairway."

Einhorn, the last person to be called to the stand in the plaintiff's case, noted that some of the revenue falls under terms of a 2008 contract covering Zeppelin's catalog of 87 songs. The band's lawyers have challenged that 2008 date, saying that it falls outside the statute of limitations.

Defense started its case this afternoon by bringing in a music expert who said that the minor descending lines in "Taurus" and "Stairway to Heaven" are common chords, and that they "couldn't be more different." Lawrence Ferrara, who had a keyboard brought into the courtroom, added that the minor descending chord progression used in both songs are "something that no one can possibly own." He also noted that opera singers, as well as Mozart, performed similar music techniques 300 years ago.

Jones took the stand at the end of the trial's first week, and claimed that he "never saw Spirit play any shows and that he never met Spirit's band members," according to writer Pamela Chelin.Jones. Jones also said that Page first played "Stairway" to him on an acoustic guitar at Headley Grange, the rehearsal and recording space where much of their early music was worked out, while he was on an electric piano.

He also acknowledged that he played the bass riff from Spirit's "Fresh Garbage," the opening track on the band's self-titled debut album, which also includes "Taurus." (Led Zeppelin used to perform the song in concert.) Jones said Page never mentioned to him, though, that he was a fan of the group.

Previously this week, jury selection hit a small bump after a potential juror was dismissed because his massive love of Led Zeppelin's music would most likely cloud his judgment, Page revealed just how huge his record collection is and somehow the 1964 movie Mary Poppins figured into the whole thing.

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