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Predatory Characteristics Of Extinct Sea Scorpion Reexamined

July 11, 2014
Image Caption (Top): This is a specimen of a pterygotid from Yale University's collections. (Bottom): Sam Ciurca, a curatorial affiliate with the Department of Invertebrate Paleontology at Yale University, holds a model of a pterygotid. Credits: Yale University

Gerard LeBlond for redOrbit.com – Your Universe Online

Scientist from Yale University studied the extinct pterygotid eurypterid, a giant sea scorpion, the largest arthropod that ever lived. It was always believed to be a fierce predator, but a recent study revealed that may not have been the case.

The paper titled, “What big eyes you have: The ecological role of giant pterygotid eurypterids,” is published in the journal Biology Letters.

Ross Anderson, a Yale graduate student and lead author of the study, covers the habits, capabilities and ecological role of this giant sea creature.

“We thought it was this large, swimming predator that dominated Paleozoic seas. But one thing it would need is to be able to find the prey, to see it,” said Anderson.

Pterygotids swam in the shallow water shorelines for 35 million years and could grow to six feet or more. Its size and long-toothed grasping claws in the front of their mouth and forward-facing eyes lead scientist to previously believe they were fierce predators. However, recent research by Richard Laub from the Buffalo Museum of Science may prove otherwise, indicating the claws couldn’t penetrate its prey as once thought and its eyesight was very poor.

“Our analysis shows that they could not see as well as other eurypterids and may have lived in dark or cloudy water. If their claws could not penetrate the armor of contemporary fish, the shells of cephalopods, or possibly even the cuticle of other eurypterids, they may have preyed on soft-bodied, slower-moving prey,” said co-author Derek Briggs, the G. Evelyn Hutchinson Professor of Geology & Geophysics at Yale and curator of invertebrate paleontology at the Yale Peabody Museum of Natural History.

Victoria McCoy, a Yale graduate student developed a mathematical analysis method to understand the creatures eyes. Yale implemented this along with using imaging technology and backscattered electrons to reveal the creature’s eye lenses without damaging the fossils. The results were compared to other extinct species of that era, as well as modern day species.

The data couldn’t reveal nearsightedness or farsightedness, but it did reveal the basic visual level of the creature’s thousands of eye lenses. “We measured the angle between the lenses of the eye itself. The smaller the angle, the better the eyesight,” Anderson said.

The research revealed that the eyesight of the pterygotids was poor, and became worse as they grew larger. In comparison to other predators such as the mantis shrimp and dragonflies, it may have not been a predator at all.

“Maybe this thing was not a big predator, after all. It’s possible it was more of a scavenger that hunted at night. It forces us to think about these ecosystems in a very different way,” Anderson added.

The vision testing Yale now uses may help to better understand how other species lived as well. “You could use it on a number of different organisms. It will be particularly useful with other arthropod eyesight examinations,” Anderson explained.

The research began as a fossil preservation class project that was taught by Briggs. Maria McNamara from the University College Cork who is a former Yale postdoctoral student also co-authored the paper.

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Source: Gerard LeBlond for redOrbit.com - Your Universe Online



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