Did Giant Octopus 'Kraken' Kill an Ichthyosaur?

Fossils suggest a giant octopus took out an enormous marine reptile.

The legendary gigantic sea monster "kraken," or at least something very much like it, might have actually existed, according to a chapter in the recently published book "Dynamic Paleontology" (Springer, 2016).

Geologist Mark McMenamin of Mount Holyoke College, who authored the chapter, "Deep Bones," believes that such a creature killed the enormous toothy ichthyosaurs of Berlin-Ichthyosaur State Park in Nevada.

Ichthyosaurs were some of the largest marine reptiles of all time, with the species at the park -- from the genus Shonisaurus -- estimated to have measured up to 70 feet long. Ichthyosaurs in general lived from about 250 to 90 million years ago and had a body shape similar to that of today's dolphins.

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Shonisaurus thrived during the earlier part of that time span, in the Triassic about 215 million years ago. The unusual arrangement of its fossils at the park has caused many to puzzle over what led to the marine reptile's demise there, especially given that it was a formidable predator in its own right.

"The leading hypothesis is that a giant octopus-like cephalopod attacked and killed the Shonisaurus ichthyosaurs and dragged their corpses to the Triassic sea floor," McMenamin writes in the book.

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He added, "The Triassic Kraken hypothesis has survived all tests to date, and currently stands alone as the best explanation for the strange collection of large ichthyosaur bones at Berlin-Ichthyosaur State Park, Nevada."

McMenamin told Discovery News that the kraken theory was formulated out of necessity because there is no viable alternate explanation for the odd arrangement of ichthyosaur bones at the park.

He says that the Triassic Kraken hypothesis is supported "by a swarm of evidence" that includes:

All ichthyosaur species are thought to have gone extinct due to climate change and their slow rate of evolution that prevented them from properly adapting to rising temperatures.

"Could climate change have killed the Shonisaurus ichthyosaurs at Berlin Ichthyosaur State Park?" McMenamin asked. "Very unlikely -- wait, no -- impossible."

He said that climate change does not explain why ichthyosaurs dominate the fossil assemblage, versus having many different types of prehistoric animal remains there. He said the nature of the assemblage also negates another theory: that toxic algae did in the ichthyosaurs.

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"Also, the constriction-cracked ribs pose a problem here, as does the fact that the ichthyosaurs were emplaced at different times," he added.

Considering the evidence, McMenamin is convinced that a kraken-like giant cephalopod killed the ichthyosaurs at what is now the site of the Nevada park. He believes that the predator belonged to an extinct lineage with characteristics of both octopuses and squids, especially glass squids, which are so named because of the transparent nature of most glass squid species.

He speculates that the big cephalopod's usual prey would have been deep water fish known as coelacanths, which Shonisaurus also hunted.

"Thus, there was an element of territoriality to this ancient interaction," McMenamin said. "The conflict between the two large predators became a meal of opportunity for the cephalopod. The kraken was evidently able to take down deep diving shonisaurs at will."

The kraken hypothesis has not been warmly embraced by McMenamin's colleagues.

"The problem with the kraken argument is it does not take into account all the other ways those vertebrae could have been re-arranged," Spencer Lucas, paleontologist and curator at the New Mexico Museum of Natural History and Science, told DNews in an earlier article.

"I suppose the kraken argument is a possibility, but one of many, and a highly unusual one."