Fossil worm adds head to its spiny appearance

New details about ancient creature give hints to evolution of some animals’ teeth

Hallucigenia sparsa, illustrated

OUT OF A DREAM  Hallucigenia sparsa (illustrated) finally has a head, thanks to a new analysis of fossils.

Danielle Dufault

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Whether it’s upside down or right side up, Hallucigenia sparsa looks like it wriggled right out of a nightmare. And giving the wormlike creepy-crawly a head hasn’t helped.

H. sparsa
INNER TEETH Even though the ancient wormlike creature H. sparsa was tiny — this fossil is 15 millimeters long — it had a fearsome feature: little teeth in part of its gut. Jean-Bernard Caron
An analysis of 508-million-year-old H. sparsa fossils from the Burgess Shale in Canada revealed that the 10- to 50-millimeter-long critter had a small pair of simple eyes set atop a narrow head. Below the head was a long neck that protruded from a tubular body sporting 10 sets of dangly appendages and seven pairs of spines. Platelike structures surrounded  H. sparsa ’smouth opening and tiny teeth lined part of its gut, researchers report  June 24 in Nature .

Those toothy features are similar to some seen in present-day tardigrades, or water bears (SN: 7/26/14, p. 4), hinting at the evolution of such gnarly mouthparts. 

WRIGGLE IT  H. sparsa rolled along on its 20 legs and may have reared up on its hind ones, as in this illustrated video. Credit: Lars Fields

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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