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."