Earliest animal footprints ever found -- discovered...(isp shadow. He immediately suspected...)

He immediately suspected that the tracks were made by an arthropod, such as one resembling a centipede or millipede, or by a leg-bearing worm.

He couldn't be certain of the length of the creature, or the number of legs it had. But judging from the tracks, he guessed that it carried its centimeter-wide body on many spindly legs.

In 2002, other researchers reported a similar fossil trail from Canada that dated back to the middle of the Cambrian period, about 520 million years ago. Another set of tracks found in South China date back to 540 million years ago.

At approximately 570 million years old, this new fossil not only provides the earliest suggestion of animals walking on legs, but it also shows that complex animals were alive on earth before the Cambrian.

Not many macroscopic fossils exist from that time because soft-bodied creatures are not normally preserved.

Babcock is an expert in "exceptional preservation" -- the special chemical, physical and biologic conditions that enabled some soft-bodied creatures to fossilize. By knowing where to look in the geologic record, he has uncovered a menagerie of unusual fossils, from unusual echinoderms in Nevada to sulfur-eating bacteria in Antarctica.

The shallow sea covering western Nevada 570 million years ago would have been a good site for exceptional preservation. The sediment surface was probably bound together by a microbial mat -- a cohesive carpet of bacteria and sediment grains. A creature's tracks could have been readily preserved when the animal pressed its legs into the sediment.

Babcock says that he is "reasonably certain -- not 100 percent" that the fossil was made by a centipede-like arthropod or a leg-bearing worm. A fossil of the animal itself would be more definitive. He is going to continue looking in the same region of Nevada, but that is not the only potential site. Similar fossils might be found in the White Sea area
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