Prehistoric rock? Post-apocalyptic fusion? Instrumental Chicago quintet Tortoise tries carving out both post-rock subgenres on its fifth full-length album. One moment, we're new-agein' it astride a pterodactyl in a blood-red sky ("Crest," "The Lithium Stiffs"). Then it's March 2118, the human race is long extinct, and grim robots wearing sun visors are sucking hard onstage at South by Southwest ("Dot/Eyes," "Salt the Skies"). The tin-skinned constructs here outnumber and therefore scuttle the Land Before Time winks. And though Tortoise's basic ingredients haven't changed -- icy xylophones, flanged spaghetti-western guitars and odd flirtations abound -- It's All Around You is the first Tortoise record to seem extraneous, the first that fails to penetrate the skin. And even at the group's most Yume Bitsu, the band sounds like it's off at the Cubs game while robot stand-ins do the heavy lifting.