IN THE LAST half of the '80s, Dinosaur Jr. roamed the earth, or at least the alt-rock universe.

They would have preferred to be simply Dinosaur, except that a psychedelic band from San Francisco laid prior claim to the name, forcing singer-guitarist J Mascis, bassist and sometimes vocalist Lou Barlow and drummer Emmett Jefferson "Murph" Murphy III to add a Jr. after the 1985 release of their eponymous debut.

They toured behind "Dinosaur" and its descendants, 1987's "You're Living All Over Me" and 1988's "Bug" (all recently rereleased with extras by Merge), and as brutally loud and explosive as the band was on stage, it often seemed even more explosive offstage, a cauldron of seething tensions and unresolved hostilities bubbling over into legendary public displays of non-affection. Finally, the domineering Mascis booted Barlow from the band. Mascis and Murph made two more Dinosaur Jr. albums (and Mascis four more basically solo albums under the name before the band called it quits in 1997). Meanwhile Barlow focused on his bands Sebadoh and the Folk Implosion.

Thanks to a Jurassic spark, the Dinosaurs are once again roaming and rocking, though Barlow reports that Mascis no longer lives to torture him as he "totally did" in the old days.

"And he very freely admits that," Barlow says. "But in my life, he's the only person that's ever done that to me, so I've kind of developed an appreciation for that. When they kicked me out of the band, I was then free to find my own voice and form bands that were based on democratic principles. But J had to send me on my way, otherwise I would have been happy just to mope around in his shadow for ages."

According to Barlow, "What happens musically with us is really cool, and now that there isn't any baggage involved, it's much easier for me to appreciate the music. And I kind of get off on being on stage with these guys again -- it's pretty funny."

For a long time, it wasn't. There was a lot of sniping over the decades, and four years ago Barlow ranted at length against Mascis in Michael Azerrad's "Our Band Could Be Your Life: Scenes From the American Indie Underground, 1981-1991," about 13 influential punk and indie rock bands that anticipated the commercial juggernaut of grunge.

"People change," Barlow says, "and J's a lot more tolerant. I made a huge mistake about how much I hated J. I hated him for the way he treated me; I actually really like him personally and Murph as well. Now there's a basic respect happening, and it's just very easy for me to forget and drop all grudges."

The reunion seeds may have been sown in 2003, when Barlow was touring in England and ended up sitting in with Mascis's Stooges cover band on "I Wanna Be Your Dog," "me screeching on top of a wall of noise that was supposed to be a Stooges song," he laughs. "But it gave me a signal: Maybe J just doesn't remember how much he hates me! Or maybe he doesn't [hate me]. When the book had come out where I was saying all this horrible stuff, I was left with such an empty feeling. When I saw that J was 'Okay, whatever, sing with us, I don't care,' I thought maybe we'll play together again."

More baby steps followed, Barlow says. "J and I have had a lot of mutual friends, people who had worked with both of us. My mother had set up a benefit show about a year and half ago that J played and Sebadoh played. And during the course of that show, J and I reunited our hardcore band for one song."

That pre-Dinosaur band was named Deep Wound, and apparently time healed those as well.

"It's kinda cool because we're starting to get back into the real ritualistic, really primal bashing again, which I've been really into," Barlow says. "I didn't realize how much I missed that feeling of being in a band that feels like a band."

Of course, being in a reunited legendary band is no longer the province of the '80s rock dinosaurs who usually tour during the summer months. You know who you are, Def Leppard (with Bryan Adams on Friday at Ripken Stadium in Aberdeen). The most surprising example has been the Pixies, the notoriously quarrelsome alternative rock quartet that after a decade managed to bury the hatchet in something other than themselves. Two lucrative tours have followed, though Barlow insists that had nothing to do with Dinosaur Jr. getting back together.

"The Pixies have never been an inspiration to me in any way, and I think that comparing their reunion to Dinosaur Jr.'s -- we're not even in the same realm of popularity or anything. People tend to lump our bands together, but we're leagues away. . . . It has nothing to do with the Pixies."

Like the Pixies, however, Dinosaur Jr. is often credited with creating the blueprint for the sound -- hard-core punk meeting classic rock over melody and old-fashioned guitar solos -- that Nirvana would take mainstream at the start of the '90s. It's particularly true of Dinosaur's middle, and best, album, "You're Living All Over Me." Again, Barlow demurs. "The most important thing is with the original lineup, we had a really particular, unique sound to the way we played together, so it is kind of cool to remind people of that. But a lot of this just feels like I'm doing it for myself."

Which is appropriate, Barlow says, agreeing that his contribution to the album, the acoustic "Poledo," anticipates what he would do in Sebadoh, and not just because of the declaration "it's great to be alone!"

"Of the records we did, it was definitely the one I knew was great," says Barlow of "You're Living All Over Me." "Our first record was essentially a demo; then we went out on tour and began to find our sound after we put that record out. 'Living' was the real beginning of the sound of Dinosaur, and I think it was because we weren't really a band that was ambitious in any way," Barlow suggests. "J was creatively ambitious, but our only ambition was to be signed to SST Records. When that happened and when people started coming to our shows and stuff, that was, to us, our peak. There was really nowhere else to go."

Were there no crossover fantasies?

"Not at all. At the time, we never entertained the idea of anybody ever crossing over. I don't think people realize that before Nirvana, nobody was hoping to be Nirvana, and what made Nirvana kind of extraordinary is that they weren't expecting that either. All we wanted to do was find our little touring circuit, a la the Minutemen and Meat Puppets and Black Flag, and do our thing and release records. There were no aspirations to get bigger than that. Nobody thought that that would happen. It was all just about playing music to people who were pretty much like us, playing music to our peers."

With the reissues and the reunion, there has been a fair amount of historical analyses and revisiting the past, particularly the volatile personal history between Barlow and Mascis, who suggested in Mojo magazine that Barlow had to leave because he felt "we would ruin his songs the way we played them."

"I didn't think Dinosaur would ruin anything," Barlow responds. "I didn't think my songs were good enough. I thought I would ruin Dinosaur! I'm only six months younger than J, but at that time it just felt like he was 30 years older. The songs he was writing were incredibly crafted -- I just thought they were beautiful. What I was writing at that time were two-chord songs on a ukulele, so I didn't feel that my songs could ever match the scope of Dinosaur, and they didn't. I didn't start writing electric songs until 1991, when Sebadoh put out 'Sebadoh 3,' and I started dabbling in electric guitar and bass again, because everything I did post-Dinosaur was either supporting my friends' songs or recording on a four track with a ukulele."

"I knew that I needed to start small, in a way that I could grasp what I was doing. In Dinosaur, our sound was so huge that I couldn't even wrap my head around it. I was very good at playing J's songs and understanding what J wanted and following through in a creative way -- I could do that. But as far as crafting songs that would become Dinosaur songs, J would have had to become a mentor to me and pull those songs out of me. We really would have had to work together a lot, and that just wasn't going to happen."

On this tour, Dinosaur is drawing exclusively from its first three albums, which means full-on doses of "In a Jar," "Little Fury Things," "Forget the Swan," "Sludgefeast" and "Freak Scene." But don't expect "Don't," the Mascis song in which Barlow had to scream an endless refrain of "Why don't you like me?"

From the first gig that we played, I blew out my voice, and it's been barely a croak for the last week and a half," Barlow reports, with what sounds like relief. "If I tried to do 'Don't,' I would probably ruin my voice, maybe for life."

But, he quickly adds, "I could get back into that mind-set in a second. Back then, I enjoyed the opportunity to really scream, and I still do -- it's total catharsis. I could be screaming something like 'peanut butter on crackers' and do it with just as much conviction as 'Why don't you like me?' It was an act of complete sadism on J's part, but I knew that and I enjoyed that.

"I've made a lot of noise in my life," Barlow muses. "Lately I've been focusing on making a statement really quietly with acoustic songs, but it doesn't mean that under the right circumstances I'm not willing to totally turn it up again. Dinosaur was a very important formative experience for me, and to revisit it is a gift."

DINOSAUR JR. -- Appearing Monday at the 9:30 club.

Dinosaur Jr. -- Emmett Jefferson "Murph" Murphy III, left, J Mascis and Lou Barlow -- is no longer a thing of the past.Murph, left, Mascis and Barlow in 1987. Mascis kicked Barlow out of the band, but now the group is together again. "People change," Barlow says.