They went drilling for oil in northern Alberta and instead dug up a one-of-a-kind, 96-million-year-old fossilized fish small enough to fit in your palm, but big enough to yield clues on how sea critters migrated in the age of tyrannosaurus rex.

But to fish paleontologist Alison Murray, the Tycheroichthys dunvenganensis is also a big question mark.

"It's complete fossil, which means it must have been killed and buried very, very quickly," said Murray, who now researches at the University of Alberta.

"It wasn't scavenged or broken apart in wave action. It must have been some sort of sudden event that killed it and trapped it in mud."

But based on the biology of its living relatives, the herring family, it is not the type of fish to have swum in muddy waters, she said.

"So I'm not sure what it was doing there. He is an anomaly."

It's a member of the extinct fish family Paraclupeidae. While other members of this family have been found in Lebanon, Morocco and Brazil, the Alberta find is a new genus entirely.

The fossil, written up recently in the Canadian Journal of Earth Sciences, was actually unearthed two decades ago south of Grande Prairie in a core sample taken 1,325 metres below the surface by now-defunct Cequel Energy Inc.

The fish was not found because Cequel was not interested in the sediment at the bottom of the core sample.

A couple of years ago, geology student Michael Hay, checking out the core samples for his own research, came across the fossil and passed it on to Murray and others.

It is now at the Canadian Museum of Nature in Ottawa.

Murray said it was swimming in a monster seaway that had cleaved what is now North America in two in the late Cretaceous period.

She said the find is further evidence of a direct water link between North America through Great Britain to the Mediterranean Sea, but also gives credence to the theory of a direct water link from the Mediterranean through what is now Hudson Bay.

"This one could support the Hudson Bay theory. We actually don't have the answer."

She said the fish will also aid research in biogeography, to help understand how organisms evolved and moved into different areas.