Newly Discovered Prehistoric Shark Species Left Teeth on Three Continents

Paleontologists have discovered a rare new species of extinct shark that roamed the oceans 20 million years ago. Dubbed Megalolamna paradoxodon, the predator was identified by its widely dispersed tooth fossils, which have been recovered from beds as far apart as California, North Carolina, Peru, and Japan.

The new species is described in a study published Monday in Historical Biology, led by paleobiologist Kenshu Shimada of DePaul University and the Sternberg Museum of Natural History in Kansas. Judging by the size of Megalolamna's pearly whites, Shimada and his colleagues think it measured about four meters (13 feet) in length, on par with a modern great white shark.

It was a close relative of the infamous 60-foot-long Megalodon, the largest shark ever known to have lived, though the two animals occupied different niches in the ancient food web.

"Although diverse large marine mammals, such as whales, that served as food sources for Megalodon had already evolved by then, [the] rather acutely pointed front teeth of Megalolamna suggests that it likely was not capable of seizing large prey like whales," Shimada told me.

"While Megalolamna likely grew to the size of typical modern-day great whites, it probably fed commonly on medium-sized fish."

This preference for mid-sized prey is reflected in the shark's name, which includes a nod to the modern "lamna" genus of sharks that possesses similarly-shaped teeth and feeds on herring, salmon, and other midrange morsels.

The "paradoxodon" part of the binomial, meanwhile, refers to the perplexing evolutionary history of the new species. Based on its teeth, Megalolamna belongs to the otodontid family of sharks; its lineage closely tied to the hulking 40-foot-long shark Otodus that thrived 60 million years ago, in the fallout of the Cretaceous-Paleogene extinction event that killed the dinosaurs.

But the fossil record seems to draw a huge blank between the eras of Otodus and Megalolamna, leaving paleontologists with little to work with when reconstructing the animal's phylogenetic background.

"When we mapped Megalolamna paradoxodon on to the otodontid family tree, we discovered a 45-million-year gap between Megalolamna paradoxodon and the presumed origination time of the Megalolamna lineage," Shimada said. "The gap suggests that there must have been one or more Megalolamna species present during the time span that we simply have not yet found or recognized."

"So, determining the evolutionary position of Megalolamna paradoxodon in the otodontid family tree has led to more questions," he continued. "I would like to seek for fossil evidence that would fill in the gap."

Let's hope the fossil shark tooth fairy comes through on this one, because it would be interesting to know how this enormous bygone shark became so successful that it left its remains on at least three continents.

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