Scientific American - 09.2019

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GILBERT S. GRANT

Science Source

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Motion in

the Ocean

Fossils clarify some of animals’

earliest deliberate movements

About 550 million years ago animals

were relegated to the seas. Microbes and

larger multicellular organisms covered

­ø`š ̧…îšxäxD‹ ̧ ̧ßž³D³ ̧ߐD³ž`­Dî䞭ž-

lar to pond scum. On top of this settled big-

ger animals, including Dickinsonia—a genus

of perplexing creatures shaped like dinner

ǧDîxäjß ̧ø³lUDîš­DîäD³l‹Dîîx³xl` ̧ž³äÍ

Scientists have long speculated about

what Earth’s life was like half a billion years

ago, during the Ediacaran period, and they

DßxäîxDlž§ā‰³lž³­ ̧ßx`§øxäÍäîølā

published online in June in Geobiology

reports that Dickinsonia may have been

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̧³îšxžß ̧ÿ³ž³äxDß`š ̧…… ̧ ̧lÍ5šžä‰³lž³j

experts say, could help us better under-

stand animals’ evolution.

Since Dickinsonia ÿxßx‰ßäîlxä`ߞUxlž³

the 1940s, scientists have debated exactly

what type of organism they were. “They’ve

been interpreted as everything from a lichen

to a worm—a whole variety of things,” says

Scott Evans, a paleontology researcher at

the University of California, Riverside, and

one of the study authors. “Recently it has

Ux` ̧­xDÇÇDßx³îîšDîä³ÿDälx‰-

nitely an animal.” Based on the fossil evi-

dence, scientists think Dickinsonia were soft-

bodied and oval-shaped, with multiple body

divisions and ribbed upper and lower surfac-

es. They had a distinct front and back and

could grow up to a meter in length but were

only several millimeters thick.

Evans and other researchers from U.C.