Two paleontologists working on the world-famous Burgess Shale have discovered a new species, the Mollisonia plenovenatrix which is now considered the oldest Chelicerat. This discovery traces the origins of this vast group of animals – over 115,000 species, including horseshoe crabs, scorpions and spiders – to a time more than 500 million years ago. The results were published on September 11, 2019 in the prestigious journal Nature .
The Mollisonia plenovenatrix would have been a wild predator for her size. The creature was thumb-sized and had a pair of large egg-shaped eyes and a "multi-tool head" with long legs and numerous pairs of limbs, all of which could feel, grasp, crush and chew. Most importantly, the new species also had a pair of tiny "tweezers" in front of their mouths called Chelicerae. These types of appendages, which are primarily used to hold and kill prey, are found only in Cheliceraten, a large group of arthropods, including modern scorpions and spiders.
"Prior to this discovery, we were unable to pinpoint the chelicerae in other Cambrian fossils, although some of them are clearly chelicerate-like," says lead author Cédric Aria, member of the Burgess Shale expeditions of the Royal Ontario Museum since 2012 currently a postdoctoral fellow at the Nanjing Institute of Geology and Palaeontology (China). "This key feature, this crest of the Chelicerate, was missing."
Other features of this fossil, including gill-like hindlimbs, suggest that Mollisonia was not a "primitive" animal. Version of a chelicerate, which in fact was already morphologically close to today's species.
"Chelicates have what we call gills or book lungs," explains Aria. "Her respiratory organs are made up of many thin sheets, like a book. This considerably increases the surface area and thus the gas exchange efficiency. Mollisonia had appendages that corresponded to only three of these leaves and probably originated from simpler limbs.
The authors believe that Mollisonia preferred to hunt near the bottom of the ocean, thanks to its well-developed legs, a kind of ecology called Benthic Predation. Mollisonia's "modern" traits suggested that Chelicerates "quickly flourished and filled an ecological niche that was under-utilized by other arthropods at the time." The authors conclude that the origin The Chelikate must be even lower in the Cambrian than the heart of the "explosion" actually occurred.
Aria says, "Finding a fossil site like the Burgess Shale at the beginning of the Cambrian would be like looking into the eye of the cyclone.
The importance of Burgess Shale and similar occurrences like the Chengjiang Biota in China lies in its exceptional conservation of the earliest marine communities in a period of uniquely rapid diversification of body forms known as the "Cambrian Explosion." Fossil animals from these Areas are characterized by the preservation of a variety of morphological features such as limbs and Eyes out, but also viscera and much less nervous system tissue.
Mollisonia was first described more than a century ago by the discoverer of the Burgess Shale, Charles Doolittle Walcott. So far, however, only rare exoskeletons of this animal were known. "This is the first time that any indication of limbs and other soft tissues of this type of animal has been described that has been crucial in uncovering its affinity," says co-author Jean-Bernard Caron, Richard M. Ivey, Curator of Inverted Paleontology at the Royal Ontario Museum (Canada). The exceptionally well-preserved fossils come from a new location in Burgess Shale near the Marble Canyon in Kootenay National Park, British Columbia.
"The Marble Canyon is the biggest headlight of my career so far. This area provides us with wonderful treasures year after year, "says Caron, who has led the Burgess Shale expeditions of the Royal Ontario Museum for 10 years. "I did not think that one hundred years later we would rediscover the Burgess Shale in this way with all the new species we find."
The specimens of Mollisonia plenovenatrix described in this new survey are better preserved than those found in the original Walcott Quarry, located approximately 40 kilometers northwest of Marble Canyon Quarry. Many other fossils found in the Marble Canyon and surrounding areas have already played an important role in our understanding of the early development of many animal groups. These include in particular the vertebrates, which are our own lineage thanks to numerous and exceptionally well preserved specimens of primitive fish . Metaspriggina walcotti . Many new species are waiting to be described; The latest, a "flying saucer", a new predatory arthropod with huge, rake-like claws, called Cambroraster falcatus was released on July 31, 2019.
The fossils of the Burgess Shale are located within the Yoho and Kootenay National Parks and are managed by Parks Canada. Parks Canada is proud to partner with leading scientists to expand the knowledge and understanding of this key period in Earth's history and to share these places through award-winning guided walks with the world. The Burgess Shale was declared a UNESCO World Heritage Site in 1980 for its outstanding universal value and is now a World Heritage Site for the larger Canadian Rocky Mountain Parks.
Mollisonia will be among the many extraordinary fossils belonging to the Burgess Shale should be exhibited in the future new gallery of the ROM, The Willner Madge Gallery, Dawn of Life, which is expected to open in 2021.
The Royal Ontario supported the research and fieldwork authoritative Museum (Research and Collection Scholarships, Natural History Research Grants), Polk Milstein Family, National Geographic Society (No. 9475-14 at JBC), Swedish Research Council (to Michael Streng), National Science Foundation (NSF-EAR-1554897) and Pomona College (to Robert R. Gaines). The research was also supported by Caron's NSERC Discovery Grant (# 341944) and the Dorothy Strelsin Foundation (ROM). Aria's research at the Nanjing Institute of Geology and Palaeontology is supported by a grant from the International Fellowship Initiative of the President (No. 2018PC0043) and a scholarship from the China Postdoctoral Science Foundation (No. 2018M630616).
Book Gills "by Cédric Aria and Jean-Bernard Caron, September 11, 2019, Nature .
DOI: 10.1038 / s41586-019-1525-4