The shark was about twice the length of a normal great white shark.
"If you think about how long we've been looking for fossils around the world as a civilization-which is maybe 200 years-in (that time) we have found just three (sets of) fossils of this kind on the entire planet, and this most recent find from Australia is one of those three", Fitzgerald told CNN.
Museums Victoria was his next call; it eventually sent out a team to excavate the area, and several more 3-inch (9cm) teeth showed up right in the same spot, indicating the shark had died right there, 25 million years ago.
That was just one of multiple teeth Mullaly found that day in 2015.
"By donating his discovery to Museums Victoria, Phil has ensured that these unique fossils are available for scientific research and education both now and for generations to come". First of all, this is the first time that fossilized teeth belonging to this mega-shark species have turned up in Australia.
Secondly, these rare fossils are among a handful of ancient shark teeth to have been found as a set. That cartilage does not easily decompose, which is why individual shark tooth fossils are somewhat common.
"Angustidens was a bloody big shark, we're talking more than 30 feet long", said Dr. Erich Fitzgerald, Senior Curator of Vertebrate Palaeontology at the Museums Victoria in Melbourne, Australia.
This makes the newfound fossils all the more extraordinary, as multiple shark teeth coming from the same specimen are notoriously hard to find.
The teeth belonged to Carcharocles angustidens, an extinct species that's closely related to the famous giant C. megalodon. The theory is that the other sharks came to feast on the carcass of the dead mega shark and lost teeth during the feast.
"The stench of blood and decaying flesh would have drawn scavengers from far around", he said.