Among the latest additions to the Chrysalis roster are the legendary J Mascis and his reformed band Dinosaur Jr.  Way back in 1984, long before the folks in Seattle were raiding thrift stores for flannel, the Amherst, Mass.-based trio laid the groundwork for a seismic shift in the underground rock, drawing up the sonic blueprint for what would become known as “alternative rock” over the next decade. Dino Jr. single-handedly moved the indie scene from the rigid ideology and rapid-fire bursts of hardcore and post-punk into a new era of introspective yet no less powerful expression.

Instead of dismissing the influences of ’60s and ’70s rock, as the first-generation punks had done, Dinosaur Jr. embraced the heavy guitar riffs and melodic underpinnings of a bygone era, and created a full on sonic assault. Cranking out walls of shuddering feedback like Neil Young & Crazy Horse on a massive bender, the Massachusetts-based trio was a crucial link between the proto-noise of Sonic Youth in the ’80s and the pugnacious metallic roar of ’90s grunge. Hearing squalling anti-anthems like the college-rock hit “Freak Scene,” you can easily imagine Mascis lurching from one foot to the other in front of looming Marshall stacks, his lank, shoulder-length mane swinging over his face. The ginormous billows of sound he manages to wrench out his guitar dwarf his proto-slacker’s voice, giving the impression the only reason he’s singing at all is because rock songs are supposed to have words, and a voice to sing them—essentially an excuse to make a whole lotta noise.

Dino Jr. bass player Lou Barlow went on to form Sebadoh, helping to lay the foundation for the lo-fi movement of the early ’90s, but the prodigal bassist has returned, restoring the original lineup, which last year cranked an album of all-new material, Beyond. The reunion was undertaken on a tentative basis in ’05, but things went well, so the band continued touring into ’06, getting stronger and more confident with each gig. When their equipment van was swiped a couple days before the Osheaga Festival in Montreal, it didn’t faze them. “That show was amazing,” say SY’s Kim Gordon, who was there. “It was almost like they’d been reborn as a hardcore band.”

From the staggeringly paced guitar spew that opens “Almost Ready” to classic soft/throb dynamism of “What If I Knew,” Beyond is an exquisite slab of pure Dinosaur Jr. It’s hard to understand the alchemical relationships that exist within certain bands. Some groups can change lineups without anyone noticing. But that was never really the case with Dinosaur Jr. The pieces that fell away over the years were missed. But now they have all been collected together in one place. For how long no one can say. So just dig it while it is.

In recent years, Mascis had led J Mascis and the Fog while moonlighting as a member of the Black Sabbath-inspired Witch—on drums, no less.  Witch’s second album, Paralyzed, came out in March.