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A spiky, armor-plated "walking tank" with bulging eyes, a shield on its butt and a head like a Swiss army knife scuttled along the seafloor more than 500 million years ago, snapping up a deadly pair of mouth pincers called chelicerae .
Researchers discovered astoundingly well-preserved fossils of these thumb-size predators in 2012, and a new study recently described the creatures, determined to be a previously unknown species dubbed Mollisonia plenovenatrix. Scientists have found dozens of fossils of this species in the United States, which is being preserved in the mouth, along with the animals' multiple legs and bulbous eyes.
The mouth pincers, in particular, caught scientists' attention. Chelicerae are found in a diverse group of animals called chelicerates; the group includes more than 115,000 species alive today, among them spiders, scorpions and horseshoe crabs. These fossils provided the oldest evidence to date of these mouth appendages. But these robust pincers may have originated in an unknown species that is even older, the study said.
Related: Image Gallery: Cambrian Creatures: Primitive Sea Life
M. plenovenatrix had a segmented body covered with protective plates. Broad, spine-studded shields covered the creature's rear and head, which was topped with bulbous eyes. The animal is likely to be used in the past, the study authors reported.
The newly described species, a plumper body than other, similar Mollisonia creatures that scientists knew only from partial fossils of their shed exoskeletons. Cédric Aria, a postdoctoral fellow with the Nanjing Institute of Geology and Palaeontology at the Chinese Academy of Sciences, told Live Science in the United States of America. an email.
Not only were chelicerae exquisitely preserved, but the creature also has gill-like respiratory structures that were surprisingly similar to those in modern chelicerates. This hinted that chelicerae likely first appeared in a species that predated M. plenovenatrix, the study said.
The rocks have eyes
Researchers uncovered the first evidence of the Mollisonia more than 100 years ago, in Burgess Shale deposits in British Columbia. But those fossils were only empty carapaces that the growing arthropods This article was written in French by Jean-Bernard Caron, curator of the Royal Ontario Museum in Toronto.
Then, in 2012, scientists hit the Mollisonia jackpot in another Burgess Shale rental; called Marble Canyon, it sits about 25 miles from the site where the first fossil carapaces appeared. In fact, M. plenovenatrix were among the first fossils researchers found, and they spotted it because of its bulging, oversize eyes peering back at them from the rock, Caron told Live Science.
"With additional material, we have been there," Caron said.
Mollisonia plenovenatrix in the dorsal view, showing the large eyes, the legs and the small chelicerae
(Image credit: Photo by Jean-Bernard Caron, Royal Ontario Museum copyright)
Over the next six years, the researchers returned to the site and excavated 49 M. plenovenatrix specimens, most of which are preserved soft tissues. The fossils also presented the animals in different positions, providing detailed views of their bodies from multiple angles, Caron said.
Tea Mollisonia Exoskeleton fossils found in the Burgess Shale date to about 480 million years ago, while the Marble Canyon fossils date to more than 500 million years ago. "So, we are pushing back the origin of this group by 20 [million] to 25 million years, "Caron said.
Mollisonia could not have been a part of the seafloor that was home to various marine lifesuch as trilobites, bristle worms "and ice cream cone-like shelly animals called hyoliths; Mollisonia 's turn, arthropod predators such as Tokummia, an ancient relative of modern centipedes, may have used its giant mandibles to chomp on Mollisonia, Caron added.
Indeed, M. plenovenatrix was not only underwater weirdo produced by the Cambrian period (541 million to 485 million years ago). Life on Earth erupted during the Cambrian, producing numerous oddball animals such as giant, bristle-mouthed shrimp; at toothy "penis worm"; an arthropod larva with a tail like a dagger; at "beautiful nightmare" crab with soccer ball eyes; and a creature that resembled the Millennium Falcon of "Star Wars."
When it comes to animal body plans, the evolution of the Cambrian ably demonstrated that "reality often surpasses fiction" – particularly for Mollisonia, which possessed an arresting combination of "dread and beauty," Aria said.
"The past is full of complexity and surprises. Mollisonia adds an important piece to the puzzle of biodiversity, "he said.
The findings were published today (Sept. 11) in the journal Nature.
Originally published on Live Science.
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