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Fossil and Cambrian: Ancient Sea Scorpion [IN-DEPTH]

Sep 14, 2015 12:27 PM EDT

People refer to the great plains of Iowa as "the middle of nowhere," but 450 million years ago, it looked quite different, when the landlocked state was actually a shallow sea, stocked with creatures that don't quite resemble anything we know today. It was the Paleozoic Era - perhaps one of the most intriguing chapters of evolutionary history, which nearly everyone has a piece of - hidden in their own backyard -- fossilized brachiopods trapped in bits of shale. Over 12,000 species of these clam shaped creatures ruled the waters at the start of the Cambrian period, capturing worms and snails that crossed its path. Yet, less than one third of the plants and animals alive today have descendants that go this far back.

The waters, swarming with an abundance of diversity for the first time since life appeared, would have been much less salty, similar to the estuaries of Australia where river waters meet with the ocean tides. Eventually, the brachiopods became the hunted, with the onset of the Ordovician. Worm-like creatures with legs, the remote ancestors of modern tube worms, and a myriad of trilobites stalked prey in the shallow depths, allowed to thrive with an abundance of oxygen and food, enabling their large size.

In the shallow sea that is today known as Iowa City, paleontologists have identified what is the oldest known apex predator - in a meteoric crater, the remains of a six-foot long "sea scorpion," which lived 460 million years ago, nine million years older than the oldest fossilized eurypterids, a group closely related to the modern day arachnids such as spiders and scorpions. As was the case with its other ancestors, it likely had poor eyesight and preyed on fish and small insects in shallow water. The new creature, Pentecopterus, was first described in a recent issue of the journal BMC Evolutionary Biology.

Imagine if you were so fortunate as to travel back to this bygone age -- in need of a protective mask as CO2 levels were sharply higher than they are today, and came across what appeared to be a large raft, with spiked armor jutting out of its sides. Pentecopterus was named for an ancient Greek galley ship, and for the world in which it lived, it saw its share of violent storms due to building wind currents throughout the oceans and the expanding glaciers in the Southern Hemisphere. An additional nine million years of evolution means a great deal for life in this era - suggesting that Pentecopterus had a variety of unique-looking relatives, and perhaps an even greater array of food items that have yet to appear on the fossil record, which it trapped and crushed with its massive claws.

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