Scientific American - 09.2019

(Darren Dugan) #1

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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
ä ̧­x ̧…îšx‰ßäî` ̧­Ç§xĀD³ž­D§äî ̧­ ̧þx
̧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.
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