Discovered in 1909, the Burgess Shale is an infamous rock bed containing exquisite preservations of soft bodied invertebrate fossils presently after the Cambrian explosion. It has significantly clarified the early evolution of animals after the Cambrian explosion. The phylogenetic relationships of these organisms are greatly associated with our understanding of the origin of life on earth and evolution. (Brysse, 2008)
The expeditious increase of atmospheric oxygen, a clear factor responsible for the Cambrian explosion, is believed to be the key factor in the evolution of life. The increase of oxygen alongside a continuous surge in nutrient supply including phosphorus and potassium led to a rapid increase of life on Earth. Due to the dramatic change in certain Earth processes including the return-flow of seawater into the mantle, the lowering of the sea level and the presence of an ozone layer, life was able to invade onto the various habitat systems. In particular in the marine environment life was able to survive, because the mountain building of Gondwana brought nutrients to the oceans and a change in ocean chemistry. This included the discovery of the organism Opabinia regalis which was believed to be strange in its appearance due to the presence of five compound eyes and a frontal nozzle. (Maruyama, et al., 2014)
Opabinia regalis originally stems from the phylum Arthropoda in the Burgess Shale fauna. An arthropod is separated from other phylum groups due to the presence of a sclerotised exoskeleton and jointed appendages. However according to (Whittington, 1975) Opabinia regalis was described as an “anostracan brachiopod or a trilobite”. (Walcott, 1975) then went on to classify the organism as “another brachiopod crustacean belonging to the order Anostraca”. Consequently Opabinia regalis was placed into a separate phylum due to its anatomical uniqueness. Whittington made a diagram which describes numerous arthropod lineages as parallel lines leaving no evolutionary connection between each separate species, including Opabinia regalis.
Due to the fact that Opabinia regalis stems originally from the Arthropoda lineage the evolutionary trend follows that of the Arthropoda. Arthropoda have many anatomical similarities between soft bodied animals including Onychophora and Tardigrada, both worm-like species believed to be ancestors of Arthropoda. Many features belonging to both worm taxons including a segmented body, paired appendages and a chitinous cuticle which molts during ecdysis are the same as that of Opabinia regalis. The evolvement is believed to have occurred during the Precambrian/Cambrian era approximately 542 million years ago following traces of embryo yolks and segmented worm bands. Sclerotisation is seen as an evolutionary trend of Opabinis regalis, which is the development of the jointed segmental sclerities. This had many great effects on the ecology, physiology, anatomy and behaviour of most Arthropods. (Chen, 2011). The presence of five compound eyes is also seen as an evolutionary trend of Opabinia regalis and is believed to originate from ostracad lineages. (Oakley, et al., 2001) Finally the most fundamental feature of the Opabinia regalis is the proboscis, a nozzle like structure located on the anterior of the organism. It perhaps evolved as a suspension feeder for the organism due to its extended length. (Krenn, et al., 2012) It is through the various evolutionary trends of the Opabinia regalis we can distinguish how this organism developed.
References
Brysse, Keynyn, 2008. From weird wonders to stem lineages: the second reclassification of the Burgess Shale fauna. Studies in History and Philosophy of Biological and Biomedical Sciences, 39, 298–313.
Chen, Yuan-Jun, 2011. The origins and key innovations of vertebrates and arthropods. Palaeoworld, 20 , 257–278.
Krenn, Harold W., Aspӧck, Horst, 2012. Form, function and evolution of the mouthparts of blood-feeding Arthropoda. Arthropod Structure and Development, 41, 101-118.
Maruyama, S., Sawaki, Y., Ebisuzaki, T., Ikoma, M., Omori, S., Komabayashi, T., 2014. Initiation of leaking Earth: An ultimate trigger of the Cambrian explosion. Gondwana Research, 25, 910-944.
Oakley, Todd H., Cunningham, Clifford W, 2001. Molecular phylogenetic evidence for the independent evolutionary origin of an arthropod compound eye. Department of Biology, Duke University, Box 90325, Durham, NC 27708-0325.
Walcott, C.D, 1931. Addenda to descriptions of Burgess Shale fossils. Smithson, misc, Collins, 85, 1-46.
Whittington, H.B, 1975. The Enigmatic Animal Opabinia regalis, Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society, Biomedical Sciences, 271, No. 910, 1-43
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