Scientists say the fossils found at Maungataniwha Native Forest in the wake of Cyclone Gabrielle could be from two different species of huge, marine reptile.
Fossil hunter Pete Shaw from Forest Lifeforce Restoration Trust was part of the team who discovered them in a creek bed while surveying the area for damage after the February storm.
He said GNS scientists studying the fossils, going by photos taken by the discovery team, had now tentatively identified them as vertebrae from two species - an elasmosaurus and a mosasaurs - both more than 70 million years old.
There had not been a flood like that through that part of Hawke's Bay since Cyclone Bola in 1988, Shaw said.
"We were looking at the huge damage caused to our roading and track network there," he said.
"But we thought with such a big flood, maybe we should just poke our noses down into the Mangahouanga stream, which is the creek that's produced all these fossils in the past, and see if anything new has turned up."
The storm had turned over boulders as big as shopping trolleys, he said.
"The creek had been pretty much stable and was growing back over since Bola, and this thing just turned it all upside down basically, just blew out everything."
This meant some good spots for finding fossils had been covered over, but new ones would have emerged.
Shaw said it was more common for marine fossils to be discovered than those of land-dwelling creatures.
"Conditions have to be just right for them to be preserved, and we're just very, very fortunate that the property I work on has these fossils there in the geology."
The rocks containing these newly-discovered fossils had been helicoptered out of the river valley to protect them from the elements.