Unveiled in late 2008, Prehistoricisms is Intronaut's second full album (2006's Null was an EP and 2007's The Challenger mixed mostly live cuts with leftovers) and it begins a new chapter in the L.A.

band's career, following the departure of founding guitarist/vocalist Leon del Muerte; a new chapter marked by change from the very first note of placid instrumental intro "Primordial Soup." That's right -- "placid" -- not a term one could often associate with the brutal onslaught and hyperactive musicianship that dominated Intronaut's first releases, making them sound like the living bridge between Lethargy and Mastodon, in heavy metal's evolutionary ladder.

Yes, Prehistoricisms still provides some aesthetic continuity for that familiarly corrugated template in a few exceptions to the new rule like "Cavernous Den of Shame" and "Australopithecus." But the more prevalent trend here sees tracks like "The Literal Black Cloud," "Sundial," and title cut blending these lingering aggressive complexities with passages both less frenzied and more atmospheric, slowly blurring the lines separating Intronaut from the epic post-metal of Neurosis.

Still, if the astounding album centerpiece, "Any Port," proves anything, it is that Intronaut's mind-boggling talent for executing controlled improvisations over meticulously disciplined foundations represents the unchallenged jazz/metal benchmark of their generation -- on a level not heard since Florida's Atheist, some 15 years earlier.

But wait -- it's not over! The concluding, 16-minute colossus, "The Reptilian Brain," gradually transforms from Indian raga to psychedelic prog-metal with improbable elegance; proving all the while that vocalist/guitarist Sacha Dunable, new guitarist Dave Timmick, and drummer Danny Walker may all be masters of their craft, but it is bassist Joe Lester whose singular skill promises to achieve full on musical immortality before he's through.

In sum, although Prehistoricisms' title, and even many of its songs' lyrics, suggest a return to, or at least praise of primal origins, Intronaut's latest offering is in fact the most adventurous and forward-looking -- not to mention accessible -- statement of their brief career, with much many more breakthroughs sure to follow.