New analysis of a shrimp-like, 508-million-year fossil in Toronto's Royal Ontario Museum has resulted in a surprising find: embryos with eggs preserved in its body. Scientists say that makes the remains the earliest evidence of brood care in the fossil record.
The brood-caring critter was an early arthropod called Waptia fieldensis. It was found in the renowned Burgess Shale deposit in Canada, and the remains had rested quietly in the museum for about 100 years before museum scientists, alongside researchers from the University of Toronto and France's National Center for Scientific Research, took a new look.
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"As the oldest direct evidence of a creature caring for its offspring, the discovery adds another piece to our understanding of brood care practices during the Cambrian Explosion, a period of rapid evolutionary development when most major animal groups appear in the fossil record," said Jean-Bernard Caron, curator of invertebrate paleontology at the Royal Ontario Museum and associate professor at the University of Toronto, in a statement.
Waptia fieldensis, from the same group as lobsters and crayfish, had a two-part structure - a bivalved carapace, or hard shell - covering the front segment of its body. Scientists think the structure was key to the creature's care of the eggs.
"Clusters of egg-shaped objects are evident in five of the many specimens we observed, all located on the underside of the carapace and alongside the anterior third of the body," said Caron.
The researchers observed at most 24 eggs carried by each animal, the clusters of eggs grouped in single layers on either side of its body.
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Researchers say their find opens a new window on the different approaches taken to brood care by early arthropods.
"The relatively large size of the eggs and the small number of them, contrasts with the high number of small eggs found previously in another bivalved arthropod known as Kunmingella douvillei," said the study's co-author, Jean Vannier, of the National Center for Scientific Research.
"And though that creature predates Waptia by about seven million years," Vannier added, "none of its eggs contained embryos."
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Kunmingella douvillei also chose to carry its eggs further back on its body, attached to its appendages.
The researchers suggest that the different strategies employed by Kunmingella douvillei and Waptia fieldensis point to quick, independently evolved methods for parents to care for their offspring. They also say the bivalved carapace played a large role in how early arthropod brood care evolved.
The scientists' work has been published in published in the journal Current Biology.