Earliest tracks of 4-legged stroll.

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Our four-legged, five-toed ancestors conquered the land earlier and more independently than expected, say paleontologists studying newfound 345 to 359-million-year-old tracks at an eroding beach in eastern Canada. At least six different kinds of four-limbed reptile-like animals -- a.k.a. tetrapods -- with five digits on their feet left their tromping prints in the mud of what was once a tropical swamp at Blue Beach, Nova Scotia. The five-digit tracks range in size from four inches to less than an inch and seem to contradict the prevailing idea that the first tetrapods had wide variety of other-than-five-toed (polydactyl) feet, out of which five-toed (pentadactyl) animals later won out as the most efficient on land.