Giant Shrimplike Predator Was a Weakling After All

[somedeafdudefromPNW]

Before I head off to a meeting...

Supposedly shell-crushing jaws had little force, model shows.

Anomalocaris canadensis trolls the seafloor in an illustration.
Illustration by Marvin Mattelson, National Geographic
Ker Than
for National Geographic News
Published November 3, 2010

A shrimplike creature thought to be Earth's first great predator was actually more of a worm-eating wuss, scientists say.

Anomalocaris canadensis glided along the seafloor about 500 million years ago, during Earth's Cambrian period. Nearly three feet (one meter) long, the shelled, bulging-eyed animal was giant compared to the other organisms living at the time. (See a prehistoric time line.)

Its unusual, O-shaped mouth was composed of 32 overlapping plates and protected by two spiky prongs that hung down from its face.

Scientists had assumed the well-armored mouth could crush and feed on other hard-shelled organisms. For instance, the ancient beast was thought to feast on organisms such as trilobites, segmented invertebrates that also lived on the seafloor.

(Related picture: "Biggest Trilobite Sea Beasts Found ... in Swarms."

But paleontologist James "Whitey" Hagadorn, of the Denver Museum of Nature & Science, and his team may have quashed this theory using a 3-D computer model of the creature's mouth.

"We're basically saying that Anomalocaris may not have been the king of the jungle," Hagadorn said.

"That doesn't mean it's not a really cool fossil ... but all the popular animations and videos that show it ferociously swimming through the oceans and ripping apart hapless trilobites may need to be reevaluated."

Weak Jaws Couldn't Crack a Shrimp

The computer model of Anomalocaris' mouth showed it was not capable of cracking the soft shell of a modern shrimp—let alone the harder shells of most trilobite species.

In fact, it couldn't even fully close its mouth, according to the new research, which Hagadorn presented this week at the annual meeting of the Geological Society of America in Denver.

So while Anomalocaris may have been able to suck up very small or freshly molted— and thus soft—trilobites, "it had no chance in heck of biting through about 95 percent of trilobite shells. Its mouth would have broken first," Hagadorn said.

(Related: "Komodo Dragon's Bite Is 'Weaker Than a House Cat's.'")

He added that supporting evidence for the model's results can be seen in the fossils themselves. For example, the team also studied more than 400 fossilized Anomalocaris mouth parts and could not find any signs of chips or scratches, which would be expected if the creatures had been continually pulverizing hard shells.

Furthermore, there is no evidence from fossilized stomach contents or feces that Anomalocaris ate anything hard.

Instead of trilobites, Anomalocaris likely fed on something soft, Hagadorn said.

"One hypothesis is that it was eating soft worms, or maybe plankton, that it was combing out of the waters."

If anything lurking in shallow Cambrian seas looked like a monster, Anomalocaris canadensis was it. The 3-foot-long, lobe-winged, shrimp-like creature came equipped with two barbed feelers and an armor-plated mouth — parts paleobiologists once thought were ideal for finding and crunching tasty trilobites.

But a new 3-D model of the creature’s mouth parts, presented Nov. 1 at the Geological Society of America’s annual meeting in Denver, Colorado, may restrict the ancient predator’s diet only to mushy meals.

“We found that it’s extremely unlikely Anomalocaris could eat most trilobites,” said James Whitey Hagadorn, the research team’s leader and a paleontologist at the Denver Museum of Nature and Science. “It couldn’t close its mouth all of the way, its mouth was too soft to crush trilobite shells.”

Jean Vannier, a paleontologist at Université Lyon 1 in France who was not involved in the work, said Hagadorn’s conclusions make sense.

“What was the function of the powerful frontal appendages of Anomalocaris? They seem to be directed towards the mouth but there [is] no clear evidence that they might be used for crushing food,” Vannier wrote in an e-mail. “To me their main function might have been to stir up the bottom sediment.”


Hagadorn said the mouth parts are often illustrated as capturing trilobites and other Cambrian critters, but emphasized that little if any research backs up the popular depiction. Instead of eating solid food, Hagadorn suspects Anomalocaris stuck to softer items on the menu 500 million years ago, much the same way modern arthropods such as shrimp, crabs and lobsters do.

“They mostly eat soft things, worms in the mud or soft microorganisms floating in water,” Hagadorn said. “We have no positive evidence Anomalocaris did eat this way, but that’s not surprising. How are you going to tell the difference between mushed-up worms, mushed-up phytoplankton or mushed-up snails in the fossil record? They’re all going to look like mush.”

To reconstruct Anomalocaris‘ ancient mouth parts, Hagadorn and his team examined 400 fossils of the structures, picked the best-preserved ones, then plugged the data into a 3-D computer model. They also did the same for 12 groups of trilobites, “including spiny ones, flat ones, round ones, and so on,” Hagadorn said, noting the shell strength was modeled after crab and lobster shells.

“Basically, we tried to capture the full range of prey sizes and shapes as well as predator mouth sizes and shapes,” he said.

The computerized model’s stress tests showed Anomalocaris‘ two feelers were very inflexible and the armored mouth, at least for non-juvenile trilobites, would break before the trilobites did.

“There’s that, plus no positive evidence in fossilized gut contents, feces or otherwise suggesting that Anomalocaris could eat trilobites or anything else with shells or cuticles,” Hagadorn said.

Some trilobite fossils have bite marks and scars resembling Anomalocaris‘ nibble. Hagadorn suggested that perhaps the creature “ingested things and then spit them out,” including hard-shelled trilobites, but never ate them.

Jean-Bernard Caron, a paleontologist at the Royal Ontario Museum in Toronto who was not involved in the work, said that doesn’t mean Anomalocaris never ate trilobites, however.

“The animal was likely well-adapted for preying on soft preys,” Caron wrote, noting that trilobites did shed their carapace during molting. “It is possible that they could have preyed upon them during that time … and before the carapace mineralized again, thus explaining numerous healed injuries on trilobites.”

Paleobiologist Danita Brandt of Michigan State University in East Lansing, who was independent of the research team, joked that “no court of law” could convict a predator of trilobites. But she said Hagadorn’s work is an important step in getting there.

“His model takes a lot of the guesswork out of the equation of what Anomalocaris was capable of,” Brandt said. “I think what he’s done here is fantastic.”

Images: 1) Illustration of the bottom of Anomalocaris canadensis, with two feelers and an armor-plated mouth./Wikimedia Commons/Nobu Tamura. 2) Anomalocaris’ distinctive pineapple-ring-like mouth, in the open position, with the four cardinal plates visible./Hagadorn et al. 3) Fossils of trilobites, creatures Anomalocaris may not have been able to eat while hard-shelled./Flickr/kevinzim.

I am disappoint. This is one of my favourite animals.

Source: Giant Shrimp-like Sea Predator Was a Weakling After All

Source: http://www.wired.com/wiredscience/2010/11/anomalocaris-trilobite-bite/

 

[Bottesini]

Sad life for the big shrimp.