Half a billion years ago, in the earliest days of animal life, there were few undersea predators. A strange shrimp-like creature that grew up to 6 feet in length and wielded twin claws served as top predator. Meanwhile, small chaetognath worms snapped at prey with a mouth that bristled with spines.
But these sparse ranks have just gotten a little less sparse.
A new fossil discovery has confirmed that a much more familiar predator, a type of jellyfish, also stalked the oceans more than 500 million years ago. The new species, Burgessomedusa phasmiformis, comes from the Royal Ontario Museum and fossils first discovered in the 1980s and '90s by Desmond Collins, the museum’s former director of invertebrate paleontology. Like many such finds revealing creatures from the early oceans, B. phasmiformis originated in the Burgess Shale deposit in the Canadian Rockies.
Akin to Modern Jellies
The jellyfish fossils are especially remarkable for having preserved delicate creatures that are 95 percent water. Collins and colleagues recovered 182 of the jellyfish, which could grow up to 8 inches in length and possess more than 90 “finger-like tentacles,” according to the paper.
These features classify the early animal as a medusozoan, a clade that still prospers today with such famous members as the Portuguese man o’ war and the moon jelly.
"Although jellyfish and their relatives are thought to be one of the earliest animal groups to have evolved, they have been remarkably hard to pin down in the Cambrian fossil record,” said Joe Moysiuk, a researcher at the museum, in a statement.
During the Cambrian period, an explosion of diversity occurred in the world’s oceans while the surrounding land remained barren of plant and animal life. Underwater, oxygen levels went through their own explosion and allowed for more complex life to evolve.
Saved By Mud
Among these species, predators such as B. phasmiformis were relatively rare, and the jellyfish may have faced little in the way of competition. At some point during its life, a sudden mud fall buried it along with many other organisms and preserved them for distant generations.
“Finding such incredibly delicate animals preserved in rock layers on top of these mountains is such a wondrous discovery,” said Jean-Bernard Caron, the museum’s Richard Ivey Curator of Invertebrate Paleontology. “This adds yet another remarkable lineage of animals that the Burgess Shale has preserved chronicling the evolution of life on Earth.”
Because land was so barren during the Cambrian Period, it eroded heavily and sometimes sent mud slides down into the ocean. At the location that later became the Burgess Shale, the mud slid down into a great basin and buried many early animals. Over millions of years, the world’s landmasses shifted dramatically and eventually raised the site to where it is today.
Between 1909 and 1967, explorers and scientists began to classify the site, which contained the fossils of many early arthropods, the phylum shared by modern-day shrimp, lobsters, crabs and insects. Overall, the massive fossil bed measures some 500 feet high and 6 feet deep.