In 2015 Philip Mullaly was strolling along a beach in Victoria, Australia, when he spotted what looked like a shining serrated blade stuck in a boulder. Using his car keys, Mullaly carefully pried from the rock a shark tooth about the size of his palm.

He did not know it at the time, but the tooth he uncovered once belonged in the mouth of a 25-million-year-old giant shark that was twice the size of a great white. “It was an awesome creature, it would have been terrifying to come across,” he said.

Mullaly, a teacher and amateur fossil hunter, returned a few weeks later and to his surprise dug up several more 3-inch teeth. “It dawned on me when I found the second, third and fourth tooth that this was a really big deal,” he said.

He contacted Erich Fitzgerald, a paleontologist at the Museums Victoria in Melbourne, who identified the teeth as belonging to a type of megatoothed shark called the great jagged narrow toothed-shark, or Carcharocles angustidens.

“Angustidens was a bloody big shark, we’re talking more than 30 feet long,” Fitzgerald said.

Fitzgerald also determined that all of the teeth most likely came from the same individual shark. Though people have found single shark teeth belonging to the megatoothed shark before, Mullaly’s find was the first time a set had been discovered in Australia, and only the third time a set of teeth belonging to the same individual Carcharocles angustidens that had been found in the world.

“I said to him, ‘You realize how important and rare these are?’ ” Fitzgerald said. “ ‘We need to go back down there and dig.’ ”

So with a team of paleontologists, Fitzgerald and Mullaly last year returned to the beach south of Melbourne. When the tide was low enough, the team uncovered more than 40 shark teeth from the boulder and part of the giant shark’s vertebrae. Fitzgerald said that each Carcharocles angustidens tooth they found came from a different spot in the shark’s jaw, which meant that all of the teeth most likely came from the same individual megashark.

“The teeth were finely serrated and sharper than a steak knife,” Fitzgerald said. “They are still sharp, even 25 million years later.”

Mullaly donated the teeth to the Melbourne Museum, where they are on display until Oct. 7.

Among the treasure trove of megashark teeth, the team also found prehistoric teeth belonging to a sixgill shark, which is a bottom-feeding scavenger that still swims off the coasts of Australia today. Although the team found evidence that there was only one megashark there, they found indications that there were several different sixgill sharks on the scene. The findings paint a gruesome picture of what the paleontologists think occurred at this spot.

Though it was the fiercest predator in the sea during its time, this colossal shark must have died and sunk to the seabed. There, a school of sixgill sharks, each with sawlike teeth, sliced its rotting flesh apart and feasted upon its carcass.

“It’s shark eating shark,” Fitzgerald said.