Saturday, July 23, 2011


Eldonia is an odd genus of animal that lived from the Cambrian to the Ordovician. When Charles Doolittle Walcott first found Eldonia in the Burgess Shale, he classified it as a holothurian (a sea cucumber), but other scientists didn't agree. They classified it as a medusoid (a jellyfish). Others classified it as a siphonophore. But no one knows for sure what it was.

There are three species of Eldonia: Eldonia ludwigii, Eldonia eumorpha, and Eldonia berbera. Although many people believe that Eldonia was a pelagic animal, some now believe that it was benthic and lived on the bottom of the ocean.

Some fossils of Eldonia show the lobopod Microdictyon feeding on them. Eldonia could grow up to 4 inches, but most specimens of Eldonia are smaller than this.

The part of the Burgess Shale where Walcott found so many Eldonia is called "The Great Eldonia Layer." Eldonia has also been found in China and in Morocco.


  1. I've got another picture that shows Eldonia (along with other Burgess creatures) on my blog:
    The reconstructions may be somewhat outdated (you'll notice Nectocaris) but it's a cool image.

  2. Eldonia and its relatives were benthic, and not pelagic as once thought.

    Researchers began to suspect that it was not pelagic due to the arrangement of encrusting animals on specimens of the Chinese Rotadiscus. Because these barnacle-like animals were found near the edges, and never on the center lead one researcher to believe that the animals lived on top of the mud. If eldonids were pelagic, then the encrusting animals would be scattered randomly all over the surface.
    Another researcher then realized that the biomechanics were all wrong, too, in that, if Eldonia was a jellyfish-like swimmer, it could not pulsate with its internal organs in a ring around what appears to be a filled center.

  3. Thanks! It's difficult to find detailed information on some of these creatures, especially for a seven-year-old. He does mention the benthic/pelagic situation in the second paragraph, and I believe it was based on this (which I guess is incorrect?):

    "Just as its affinities are enigmatic, so also is its lifestyle. While its medusoid shape suggests a pelagic lifestyle, other researchers believe it led a benthic and passive life on the sea bottom."

    Is there anything online or in a book covering what you've posted here? I know Art would love to read more.

  4. A very good book (but slightly out of date) to start with is "The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life"

    And this paper here explains the situation of Eldonia's life-habits better in more, and bigger words. The diagram on page 8 sums everything up, though.

  5. Thanks Stanton. I was glad to be able to print off the paper you gave the link to. The picture of the reconstruction of the animal is very useful.

    And Art, thank you even more. I've just become interested in the life at the time of the Burgess Shale and have got more information from your site than anywhere else.

    Keep up the good work.