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Animal origins shift to comb jellies

Genetic data confirm the marine predators have more ancient origin than simpler sponges

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2:00pm, December 12, 2013

DEEP ROOTS  The comb jelly Mnemiopsis leidyi rests at the base of the tree of animal life, according to analyses of its genome. 

Complex marine creatures called comb jellies should replace brainless, gutless, simple sponges at the base of the evolutionary animal tree of life, a new report asserts.

 

Scientists have long assumed that the ancestor of all living animals vaguely resembled sponges. Now, biologists must reformulate hypotheses on the evolution of the first animals more than 550 million years ago. “This finding makes people very uncomfortable,” says Joseph Ryan, an evolutionary biologist at the National Human Genome Research Institute in Bethesda, Md., and lead author of the study in the Dec. 13 Science.

 

For over a century, biologists have painted a picture of early animal evolution marked by the gradual addition of indispensible features. In that scenario, colonies of single-celled organisms called choanoflagellates gave way to multicellular predecessors of sponges; millions of years

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