Half-Billion-Year-Old Fossil Reveals Origin of Comb Jellies

(CN) – A 520-million-year-old fossil resembling a flower is the great ancestor of modern-day comb jellies, jellyfish-like sea creatures that cast a rainbow-like effect as they propel their way through ocean waters.

This is the holotype specimen of Daihua sanqiong. (Yang Zhao)

The fossil is made up of a cup-shaped organism with 18 tentacles of fine feather-like branches with rows of comb-like hairs surrounding a mouth.

The connection is made in a new study published Thursday in the science journal Current Biology, which analyzes a fossil found in China’s southern Yunnan province and bumps comb jellies to a new branch in the evolutionary tree of life.

Modern comb jellies derive their name from a row of comb-like plates called cilia that covers their tentacles and allows them to move their egg-shaped bodies through water the same way bacteria swims. These carnivores may look like jellyfish, but are from an entirely different class of animals.

Researchers say their newfound understanding of the comb jellies through the lens of the fossil named Daihua casts a new light on two other fossils that were thought be to part of other groups of sea creatures. Those include a 508-million-year old fossil found in the Canadian Rockies and another in the Maotianshan Shales in the same province where the Daihua fossil was found.

Several well-preserved fossils have been found in rice fields and farmlands in the tropical region of China over the last 30 years, according to the researchers from University of Bristol, Yunnan University in China and London’s Natural History Museum.

The study posits comb jellies evolved from ancestors that had organic skeletons and lived on the ocean floor where they had polyp-like tentacles. Over time, their mouths expanded into balloon-like spheres, but their bodies shrunk down so that their tentacles emerged toward the back-end of the animal.

Jakob Vinther, molecular paleobiologist from the University of Bristol, described the discovery as a real breakthrough for the understanding of the comb jellies’ journey from the seafloor.

“We pulled out a zoology textbook and tried to wrap our head around the various differences and similarities, and then, bam! Here is another fossil that fills this gap,” said Vinther.

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