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Saturday, May 28, 2011

Not So Anomalous After All

It turns out that a hefty Cambrian predator that looked a bit like a cross between a sting ray and a prawn was bigger and hardier than anyone realized. It was widely thought that the anomalocaridids had been successfully displaced by the nautiloids around 510 million years ago. Not true, it now seems.

Dinosaur-tie-donning Yale paleontologist and taphonomist Derek Briggs, who along with colleague Peter Van Roy authored the new report on the basis of fossils found in Morocco, says anomalocaridid had already "become a kind of icon of the 'Cambrian explosion' because it's the largest predator amongst those animals that appeared when all the major groups of Metazoans first appear on the fossil record." But it was also poorly understood for a long time. He notes in this brief film that various parts of the anomalocaridid were initially thought to be separate animals -- the dual barbed appendages in front of the mouth, and the mouth/jaw that looks like the shuttered aperture of a camera. We knew a lot more about them before the Morocco discovery, including that they were probably ravenous predators of soft-bodied organisms like worms and such.

Briggs says the Moroccan revelation is twofold: a) these anomalocarodids were "enormous" at well over 1 meter long; and b) they demonstrate that anomalocaridid or its relatives "persisted" well beyond when the rock record previously suggested, so at least 30 million years beyond the middle Cambrian around 510 million years ago.

"Nature" explains more about these "super-predators" and the Moroccan revelation with regard to their continued survival:
[A]nomalocaridids came in diverse shapes and sizes — from Hurdia victoria, with its triangular carapace, to Schinderhannes bartelsi, with its long, pointed tail — and lived in the areas that are now Europe, the United States, Australia and China. But ancient relatives of sea scorpions and nautiluses that emerged in the Ordovician Period (490 million–440 million years ago) were suspected to have out-competed the anomalocaridids, causing them to die out, says Van Roy.

In 2008, however, an amateur collector, Mohammed Ben Said Ben Moula, discovered specimens that looked like anomalocaridids, Van Roy says. But it wasn't until 2009, when the researchers took a trip to the Fezouata rock formation in southeast Morocco, that they realized just what Ben Moula had discovered.
"National Geographic" has more about their size and evolutionary milieu:
Previous anomalocaridid fossils had shown the animals grew to perhaps 2 feet (0.6 meter) long, which already would have made them the largest animals of the Cambrian period (542 to 501 million years ago)—an evolutionarily explosive time, when invertebrate life evolved into many new varieties, such as sea lilies and worms.

But at a foot longer than previous specimens, the largest of the new anomalocaridids suggests the segmented animals grew to bigger sizes than scientists had imagined.
So while its evolutionary line eventually died out, anomalocaridid was thriving for a lot longer than anyone was giving it credit for.

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