A previously unknown 505-million-year-old invertebrate animal, named Orthrozanclus reburrus was identified and described by Dr. Jean-Bernard Caron, palaeontologist in the Department of Natural History at the Royal Ontario Museum (ROM) and Dr. Simon Conway Morris from the University of Cambridge in England in a recent issue of Science.
In the article, the authors suggest that this tiny animal (about one centimeter in length), characterized by one anterior shell and numerous spines, may belong to a new group of organisms, the halwaxiids that is related to present-day snails, earthworms and molluscs (lophotrochozoan animals). Nine extremely well-preserved specimens of this new species were uncovered by the ROM from the world-renowned Burgess Shale fossil locality (a UNESCO World Heritage Site) in British Columbia, dating from the Middle Cambrian period. Two previously indeterminate specimens from the Burgess Shale collection at the Smithsonian Institution in Washington, D.C. were also identified to this new species.
“We’re experiencing a Renaissance of the Burgess Shale,” said Dr. Jean-Bernard Caron, ROM Associate Curator of Invertebrate Palaeontology. “The ROM’s collection is a gold mine of specimens new to science. Tens of thousands of fossils with many dozens of new species were collected by the ROM, under the leadership of Dr. Collins, the ROM’s former Curator of Invertebrate Palaeontology, over the last 30 years. Until recently, research on body-armoured animals was based on isolated skeletal parts found across the world in deposits of similar age or older than the Burgess Shale. It is exceptional to find complete and well-preserved specimens such as the ones that were available for this study. Thanks to the particular conditions for preservation of soft tissues in the Burgess Shale, we can now see how the complete animal of this new species looked like for the first time.”
The article also draws similarities between Orthrozanclus and other body-armoured organisms such as Wiwaxia from the Burgess Shale and Halkieria from the Lower Cambrian Sirius Passet in Greenland, that now form a natural group called the halwaxiids. All were slug-like with dorsal surfaces covered with sclerites, but Halkieria possessed two shells, one at each end of the body. All these animals likely grazed on seafloor bacterial growths and evolved sclerites for defense against predators.
In the July 6, 2006 issue of Nature magazine, Dr. Caron, with other colleagues, redescribed previously unrecognized features of a Burgess Shale animal called Odontogriphus, now interpreted as the world’s oldest known soft-bodied mollusc. Odontogriphus is thought to be more primitive than Orthrozanclus, and has no body armour. Odontogriphus, and the halwaxiids probably became extinct following the demise of widespread bacterial sea-floor communities after the Middle Cambrian period. These specimens will be a part of a Burgess Shale component of the ROM’s future Gallery of Earth and Early Life, opening in 2008-2009.
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