Nav: Home

Half-a-billion-year-old tiny predator unveils the rise of scorpions and spiders

September 11, 2019

Two palaeontologists working on the world-renowned Burgess Shale have revealed a new species, called Mollisonia plenovenatrix, which is presented as the oldest chelicerate. This discovery places the origin of this vast group of animals--of over 115,000 species, including horseshoe crabs, scorpions and spiders--to a time more than 500 million years ago. The findings are published in the prestigious journal Nature on September 11, 2019.

Mollisonia plenovenatrix would have been a fierce predator--for its size. As big as a thumb, the creature boasted a pair of large egg-shaped eyes and a "multi-tool head" with long walking legs, as well as numerous pairs of limbs that could all-together sense, grasp, crush and chew. But, most importantly, the new species also had a pair of tiny "pincers" in front of its mouth, called chelicerae. These typical appendages give the name to the group of scorpions and spiders, the chelicerates, which use them to kill, hold, and sometimes cut, their prey.

"Before this discovery, we couldn't pinpoint the chelicerae in other Cambrian fossils, although some of them clearly have chelicerate-like characteristics," says lead author Cédric Aria, a member of the Royal Ontario Museum's Burgess Shale expeditions since 2012, and is presently a post-doctoral fellow at the Nanjing Institute of Geology and Palaeontology (China). "This key feature, this coat of arms of the chelicerates, was still missing."

Other features of this fossil, including back limbs likened to gills, further suggest that Mollisonia was not some "primitive" version of a chelicerate, but that it was in fact already close morphologically to modern species.

"Chelicerates have what we call either book gills or book lungs," explains Aria. "They are respiratory organs are made of many collated thin sheets, like a book. This greatly increases surface area and therefore gas exchange efficiency. Mollisonia had appendages made up with the equivalent of only three of these sheets, which probably evolved from simpler limbs."

The authors believe that Mollisonia preferentially hunted close to the sea floor, thanks to its well-developed walking legs, a type of ecology called benthic predation. Because Mollisonia is so modern-looking, chelicerates seem therefore to have prospered quickly, filling in an ecological niche that was otherwise left poorly attended to by other arthropods at that time. The authors conclude that the origin of the chelicerates must lie even deeper within the Cambrian, when the heart of the "explosion" really took place.

"Evidence is converging towards picturing the Cambrian explosion as even swifter than what we thought," says Aria. "Finding a fossil site like the Burgess Shale at the very beginning of the Cambrian would be like looking into the eye of the cyclone."

The importance of the Burgess Shale and similar deposits, such as the Chengjiang biota in China, lies in their exceptional preservation of the earliest marine animal communities at a time of uniquely rapid diversification of body forms called the "Cambrian explosion." Fossil animals from these sites are notable for preserving an extensive array of morphological features, such as limbs and eyes, but also guts and, much more rarely, nervous system tissues.

Mollisonia was first described more than a century ago by the discoverer of the Burgess Shale, Charles Doolittle Walcott. However, so far, only rare exoskeletons of this animal were known. "It is the first time that evidence of the limbs and other soft-tissues of this type of animal are described, which were key to revealing its affinity," says co-author Jean-Bernard Caron, Richard M. Ivey Curator of Invertebrate Palaeontology at the Royal Ontario Museum (Canada). The exceptionally well-preserved fossils come from a new Burgess Shale sites near Marble Canyon, in Kootenay National Park, British Columbia.

"Marble Canyon is the biggest spotlight of my career so far. This area keeps giving us wonderful treasures year after year," says Caron, who has been leading the Royal Ontario Museum's Burgess Shale expeditions for the past 10 years. "I would not have imagined that we could, in a way, rediscover the Burgess Shale like this, a hundred years later, with all the new species we are finding."

The specimens of Mollisonia plenovenatrix described in this new research are better preserved than the ones found at the original Walcott quarry that is located about 40 kilometers northwest of the Marble Canyon quarry. Many other fossils found at Marble Canyon and surrounding areas have already played a critical role in our understanding of the early evolution of many animal groups. These notably include the vertebrates, our own lineage, thanks to numerous and exceptionally well-preserved specimens of the primitive fish Metaspriggina walcotti. Many new species await to be described; the latest one, a "flying saucer-like" new predatory arthropod with huge rake-like claws called Cambroraster falcatus, was just recently published on July 31, 2019.

The Burgess Shale fossil sites are located within Yoho and Kootenay national parks and are managed by Parks Canada. Parks Canada is proud to work with leading scientific researchers to expand knowledge and understanding of this key period of earth history and to share these sites with the world through award-winning guided hikes. The Burgess Shale was designated a UNESCO World Heritage Site in 1980 due to its outstanding universal value and is now part of the larger Canadian Rocky Mountain Parks World Heritage Site.

Mollisonia will be among the many exceptional fossils from the Burgess Shale planned to be on display in the ROM's future new gallery, The Willner Madge Gallery, Dawn of Life, scheduled to open in 2021.
-end-
Major funding support for the research and field work came from the Royal Ontario Museum (Research and collection grants, Natural History field work grants), the Polk Milstein Family, the National Geographic Society (#9475-14 to JBC), the Swedish Research Council (to Michael Streng), the National Science Foundation (NSF-EAR-1554897) and Pomona College (to Robert R. Gaines). 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 President's International Fellowship Initiative Grant (#2018PC0043) and a China Postdoctoral Science Foundation Grant (#2018M630616).

Royal Ontario Museum

Related Fossil Articles:

Rare lizard fossil preserved in amber
The tiny forefoot of a lizard of the genus Anolis was trapped in amber about 15 to 20 million years ago.
Reconstructing the diet of fossil vertebrates
Paleodietary studies of the fossil record are impeded by a lack of reliable and unequivocal tracers.
Fossil is the oldest-known scorpion
Scientists studying fossils collected 35 years ago have identified them as the oldest-known scorpion species, a prehistoric animal from about 437 million years ago.
Fossil fish gives new insights into the evolution
An international research team led by Giuseppe Marramà from the Institute of Paleontology of the University of Vienna discovered a new and well-preserved fossil stingray with an exceptional anatomy, which greatly differs from living species.
What color were fossil animals?
Dr. Michael Pittman of the Vertebrate Palaeontology Laboratory, Department of Earth Sciences, The University of Hong Kong led an international study with his PhD student Mr.
New Cretaceous fossil sheds light on avian reproduction
A team of scientists led by Alida Bailleul and Jingmai O'Connor from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences reported the first fossil bird ever found with an egg preserved inside its body.
Fossil deposit is much richer than expected
Near the Dutch town of Winterswijk is an Eldorado for fossil lovers.
Researchers add surprising finds to the fossil record
A newly discovered fossil suggests that large, flowering trees grew in North America by the Turonian age, showing that these large trees were part of the forest canopies there nearly 15 million years earlier than previously thought.
Chinese Cretaceous fossil highlights avian evolution
A newly identified extinct bird species from a 127-million-year-old fossil deposit in northeastern China provides new information about avian development during the early evolution of flight.
Parasites discovered in fossil fly pupae
Parasitic wasps existed as early as several million years ago.
More Fossil News and Fossil Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: Reinvention
Change is hard, but it's also an opportunity to discover and reimagine what you thought you knew. From our economy, to music, to even ourselves–this hour TED speakers explore the power of reinvention. Guests include OK Go lead singer Damian Kulash Jr., former college gymnastics coach Valorie Kondos Field, Stockton Mayor Michael Tubbs, and entrepreneur Nick Hanauer.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Dispatch 6: Strange Times
Covid has disrupted the most basic routines of our days and nights. But in the middle of a conversation about how to fight the virus, we find a place impervious to the stalled plans and frenetic demands of the outside world. It's a very different kind of front line, where urgent work means moving slow, and time is marked out in tiny pre-planned steps. Then, on a walk through the woods, we consider how the tempo of our lives affects our minds and discover how the beats of biology shape our bodies. This episode was produced with help from Molly Webster and Tracie Hunte. Support Radiolab today at Radiolab.org/donate.