Monash University researcher Lucas Buchanan was the first to identify the fossilised remains, which were unearthed by a mining company in a lakebed at Gladstone.
The almost complete skulls, one lower jaw, and parts of the legs, ribs and claws of two of the crocodiles have excited scientists studying the evolution of one of Australia's more dangerous killers, still numerous across the country's tropical north.
"It's important because it belongs to the earliest known genus of what's called Mekosuchinae - a big group of extinct crocodiles that dominated Australia and developed a large degree of diversity," Lucas Buchanan said.
Buchanan said the new species of crocodile was very similar to the modern-day freshwater crocodile, suggesting the modern crocodile had changed little in millions of years of evolution.
Not much is known about crocodiles that lived between 30 and 65 million years ago and Buchanan said the find would help fill a blank area of knowledge in evolutionary history.
"The Queensland site has provided the richest and most plentiful supply of crocodile fossils from this time in history," he said.