Walk across a beach’s wet sand, and you’ll leave behind imprints that briefly hold the shape of your feet before blurring and falling apart.
But 540 million years ago, seaside sand contained densely packed microbial communities, which created a gooey glue that was excellent for preserving impressions of ocean creatures left high and dry by retreating waves.
And on a long-gone seashore in what is now arid Death Valley, sticky sand retained impressions of the oldest known example of a jellyfish stranding, saving a fossilized snapshot of Cambrian period marine life that researchers excavated and described in a new study. [Cambrian Creatures Gallery: Photos of Primitive Sea Life]
The ancient jellyfish were preserved in a slab of sandstone found in southeastern California. Scientists identified 13 of these oval specimens on the rocky surface, ranging from 1.2 to 8.3 inches (3 to 21 centimeters) in diameter. The fossils were lighter than the rock surrounding them, and they varied not only in size but also their style of preservation. Some included convex, circular ridges; others held concave rings around a convex interior; and several were fossilized as more pronounced, rounded mounds, the scientists wrote in the study.
In one jellyfish specimen, shapes of some of the animal’s body parts were still faintly visible. Additional marks in the rock around the fossilized jellyfish hinted at the movements of ancient currents, which may have pushed and distorted the bodies of the stranded jellyfish prior to fossilization. Other marks might have been made by a stranded jellyfish’s attempts to move back into the water, according to the study authors.
Unique conditions for fossil formation
Ancient, soft-bodied animals are exceedingly rare in the fossil record, compared with animals with robust…