Burgess Shale top predator reconstructed


From LiveScience:

Ancient Creature Was a Miniature Monster

By LiveScience Staff

posted: 19 March 2009 02:01 pm ET

A fossil from famous shale deposits in Canada was thought to be unremarkable, but a new study finds that it’s actually the remains of a 500-million-year-old monster-looking predator.

The Burgess Shale (a UNESCO World Heritage Site in the Canadian Rockies of British Columbia) has yielded exceptionally well-preserved fossils that present a remarkable snapshot of Cambrian marine life from 505 million years ago.

The first fragments of the monster fossil (a species called Hurdia victoria) were described nearly 100 years ago, and at the time, they were thought to be part of a crustacean-like animal, and other parts were subsequently described as multiple organisms including jellyfish, sea cucumbers and other arthropods.

Now it’s clear that Hurdia was a relatively large predatory animal, possibly up to 1.5 feet (0.5 meter) in length. It had a segmented body with a head bearing a pair of spiny claws and a circular jaw structure with many teeth.

“Finding a complete fossilized animal is extremely rare. Soft tissues tend to decay rapidly after death, and harder parts tend to disarticulate or break into pieces, often leaving very few clues as to what the original animals looked like,” said Jean-Bernard Caron of the Royal Ontario Museum, which houses many Burgess Shale fossils, including pieces of Hurdia.

A study of the fossil by Caron and his colleagues, detailed in the March 20 issue of the journal Science, sheds light on the origin of the largest group of living animals, the arthropods — a group that includes insects, crustaceans, spiders, millipedes and centipedes.

Clues to the real nature of Hurdia have been accumulating over the years as new specimens have either been collected or discovered in museum collections. The last piece of the puzzle was found when a specimen turned up in storage cabinets at the Smithsonian National Museum of Natural History in Washington, D.C. The specimen, the best-preserved of all the relevant fragments, was collected by Charles Walcott in the early 20th century.

This specimen had lain untouched for decades until researchers in the 1970s and 80s classified it first as an arthropod and then as an unusual specimen of the famous monster predator Anomalocaris. The new description of Hurdia shows that it was actually related to this other beast.

One feature does set Hurdia apart from Anomalocaris — a unique, large, three-part shell that projects out from the front of the animal’s head.

“This structure is unlike anything seen in other fossils or living arthropods,” said Allison Daley, the team’s lead researcher from Uppsala University in Sweden, who worked on the fossils for her doctoral thesis.

“It was hard to tell whether the box-like shell structure came to lie so far forward after the animal died, or when it molted its hard parts, or if this was how it really looked when alive,” said Greg Edgecombe, a paleontologist at the Natural History Museum. “The way the fossil is preserved made us decide that it really had this structure in front of its head, but we still don’t know what it was for.”

Daley said: “In many animals, a shell or carapace is used to protect the soft-parts of the body, as you would see in a crab or lobster, but this structure in Hurdia is empty and does not cover or protect the rest of the body. We can only guess at what its function might have been.”

Also unknown is exactly what this mini predator would have snacked on.

“We have no direct evidence (such as preserved gut contents or fecal matter) as to what Hurdia would have been eating, but we can guess that as a top predator it was trying to eat anything it could catch,” Daley told LiveScience in an email. “In the Cambrian marine environment, this could include trilobites [see also here] or other arthropods, molluscs, marine worms, and even other predators.”

The Hurdia fossil also reveals details of the gills associated with the body, some of the best preserved in the fossil record. Most of the body is covered in the gills, which were probably necessary to provide oxygen to such a large, actively swimming animal.

Hurdia and Anomalocaris are both early offshoots of the evolutionary lineage that led to the arthropods. They reveal details of the origins of important features that define the modern arthropods, such as compound eyes and limbs with filaments used for breathing.

See also here.

The meters-long, carnivorous “shrimp” from hell that once ruled the seas of Earth a half billion years ago may have been a real softy, it turns out. A new 3-D modeling of the mouth parts of the Anomalocaris, along with evidence that these parts were not hard like teeth, but flexible, shows that the famed predator could not have been munching on the hard shells of trilobites and other such creatures of the early seas: here. And here.

Eight new kinds of the earliest animals from the Cambrian Explosion have been found in a newly explored section of ancient rock in Canada: here.

Transition from sea to land: Hermit Arthropods 500 Million Years Ago? Here.

Position and development of oocytes in velvet worms shed light on the evolution of the ovary in Onychophora and Arthropoda: here.

Seeking safety in numbers is an age-old maneuver—at least 465 million years old, it turns out. Ordovician-period fossils discovered in Portugal show groups of trilobites hiding out or molting together—rare clues to the ancient marine arthropods’ social and survival behaviors: here.

Ordovician ice age: here.

ScienceDaily (Jan. 18, 2012) — A bizarre creature that lived in the ocean more than 500-million years ago has emerged from the famous Middle Cambrian Burgess Shale in the Canadian Rockies. Officially named Siphusauctum gregarium, fossils reveal a tulip-shaped creature that is about the length of a dinner knife (approximately 20 centimetres) and has a unique filter feeding system: here.

The Burgess Shale of British Columbia is arguably the most important fossil deposit in the world, providing an astounding record of the Cambrian “Explosion,” the rapid flowering of complex life from single-celled ancestors. While most of the fossil record is comprised of shells, teeth and bones, the Burgess Shale preserves the softer bits—the eyes, guts, gills and other delicate structures—of animals belonging to Earth’s earliest complex ecosystems a half a billion years ago. The process for this extraordinary preservation remained a mystery since the initial discovery of the Burgess Shale in 1909 until now: here.

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12 thoughts on “Burgess Shale top predator reconstructed

  1. Ocean’s sudden cooling linked to mass extinction

    Scientists find evidence on Quebec island that 5-degree drop killed 75% of marine species 450 million years ago

    By Randy Boswell, Postmedia News January 31, 2011

    Canada’s Anticosti Island has produced the first clear evidence that the planet’s second-largest mass extinction — the sudden disappearance of 75 per cent of all marine species on Earth about 450 million years ago — was caused by a rapid, five-degree plunge in ocean temperatures.

    The discovery on the large Quebec island was reported just days after another team of scientists pointed to ash deposits on Axel Heiberg Island in the Canadian Arctic as proof that the planet’s biggest extinction event — when 95 per cent of all life died out 250 million years ago — was linked to volcano-fed coal fires in ancient Siberia.

    Anticosti Island, in the Gulf of St. Lawrence, is widely viewed as a geological treasure. The steep cliffs along the island’s shores preserve a fossil-rich record of Earth history from a time when present-day North America was situated around the equator.

    Scientists have long known that the so-called “Ordovician extinction” that killed off much of the world’s marine life 450 million years ago was somehow connected to an ice age that sharply reduced global sea levels, destroyed many coastal habitats and chilled ocean ecosystems.

    But “exactly what caused this tremendous loss in biodiversity” — the precise mechanism of extinction — “remains a mystery,” a team of nine U.S. researchers stated in a summary of their study, published in the latest issue of the journal Science.

    So the team probed Anticosti’s unmatched record of fossilized marine creatures to produce the first detailed record of average Ordovician ocean temperatures.

    Using the alignment of telltale molecules in the animals’ preserved shells as a “paleo-thermometer,” the scientists discovered that a spike in extinctions during the Ordovician era coincided exactly with the sudden cooling of the seas.

    “Our study strengthens the case for a direct link between climate change and extinction,” California Institute of Technology researcher Seth Finnegan said in the study overview.

    “Although polar glaciers existed for several million years, they only caused cooling of the tropical oceans during the short interval that coincides with the main pulse of mass extinction.”

    Finnegan said Anticosti Island, which is 225 kilometres long and larger in area than Prince Edward Island, is a “fantastic place to do geology” because it is “one of the very few places that preserves a more or less complete sedimentary record” of rock layers from the Ordovician era.

    “Thanks to the spectacular sea cliffs and river canyons,” Finnegan added, “the exposures of these rocks are excellent, allowing us to sample them much more completely than we could in many other places.”
    © Copyright (c) The Vancouver Sun

    http://www.vancouversun.com/technology/Ocean+sudden+cooling+linked+mass+extinction/4194607/story.html#ixzz1CdMaCxa3

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