Royal Society Publishing researchers have discovered the oldest species of swimming jellyfish in 505-million-year-old fossils in British Columbia. .“Our study is based on 182 exceptionally preserved body fossils from the middle Cambrian Burgess Shale,” said Royal Society Publishing researchers Justin Moon, Jean-Bernard Caron, and Joseph Moysiuk in a Wednesday study. .“Burgessomedusa possesses a cuboidal umbrella up to 20 centimetres high and over 90 short, finger-like tentacles.”.The Burgess Shale is a fossil-bearing deposit exposed in the Rocky Mountains in BC. It is famous for the exceptional preservation of the soft part of its fossils. .Moon, Caron, and Moysiuk said genetic analysis supports Burgessomedusa being organism group medusozoa, most likely as an offshoot to other forms of jellyfish..Burgessomedusa phasmiformis demonstrates an ancient origin for the free-swimming medusa life stage and supports a growing number of studies indicating an early evolutionary diversification of medusozoa. .Jellyfish belong to a group called cnidarians, which represent diverse, important animals in modern oceans and freshwater ecosystems..One of the most unique adaptations to emerge within this group is the ability to transition from sessile polyp to a muscular swimming bell in medusozoans. .The evolution of this life cycle happened once, sharing a common ancestor of all medusozoans and was later lost in many groups. .The researchers said cnidarians are thought to represent one of the earliest-diverging branches of animals, making them key for understanding the origin of bilateral species..They said the origin and early evolution of medusozoans and of the medusa stage remains constrained by the fossil record. .They acknowledged studying cniardian body fossils, especially those lacking hard body parts, remains challenging. This is because they have low preservation potential and these species are less likely to be buried and preserved. .The fossil material studied is deposited in the collections of Invertebrate Palaeontology at the Royal Ontario Museum. Some of this material was first mentioned as representing probable medusoids in an unpublished master's thesis focused on the paleoecology in the Burgess Shale, but it was never described. .Its genus is a compound name with Burgess referring to the locality and medusa referring to the group medusozoa. The species is a compound name with Greek word phasma and Latin word forma, indicating the ghostly figure of the umbrella..The researchers said specimens were preserved as flat, carbonaceous compressions and were buried at different angles along bedding planes from rapid burial. They said the majority of specimens were preserved laterally and some are preserved but none could be interpreted to be preserved vertically with their oral sides up. .These jellyfish are described as bell-shaped umbrellas with width reaching about 40% of umbrella height. More than 90 finger-like tentacles form near the oral margin, reaching about 15% of umbrella height in length. .A stomach cavity can be located at apex of the umbrella, occupying about 30% of the body area. A handle-shaped projection extends up to two-thirds the length of the umbrella..Moon, Caron, and Moysiuk concluded by saying the Burgessomedusa’s shape provides indirect evidence of rowing propulsion and predatory habits. .“Burgessomedusa shows that pelagic Cambrian ecosystems were not uniquely dominated by large arthropod predators such as anomalocaris and titanokorys, but that they also harboured a diversity of other predators including chaetognaths, ctenophores, and jellyfish,” they said.
