A dinosaur-hunting expedition to the Sahara desert involving British scientists has found the fossilised remains of what are thought to be two new species.

The ancient remains discovered in Morocco belong to a giant flying pterosaur and plant-eating sauropod. Initial examinations suggest that both specimens are unknown to science.

They were unearthed during a month-long quest during which the research team braved floods and storms to reach the dig site and then preserve the fossils. The scientists even feared that they would never get the bones out of the desert because they were so heavy that their Land Rover became stuck in sand.

Nizar Ibrahim, of University College Dublin, a leader of the project, said: “There was a point when we wondered if we would make it out of the desert with the [sauropod] bone, but we had worked so hard to find it there was no way I was leaving it behind. It took us five days to get the bone out of the ground and down the mountain – and that was not the end of our problems.”

His colleague David Martill, of the University of Portsmouth, said: “When we had managed to get the bone in the Land Rover, the extra weight meant we kept sinking in the sand dunes and on several occasions everybody except the driver had to walk while we negotiated difficult terrain. Our journey home was equally eventful. While crossing the Atlas mountains we got caught in a snowstorm and total whiteout. But it’s all been worth it.”

Another challenge was to cross flooded rivers at night to buy water and plaster that helped to preserve the sauropod bone. The team was also cut off in the desert for four days by heavy rain and flooding.

The first fossil is the beak of a pterosaur, a giant flying reptile that lived about 100 million years ago. Such discoveries are unusual because pterosaur bones were light and fragile, to be adapted to flight, and few fossilised well. Mr Ibrahim, a doctoral student, said: “Most pterosaur discoveries are just fragments of teeth and bone so it was thrilling to find a large part of a beak and this was enough to tell us we probably have a new species.”

The second significant discovery was a leg bone more than a metre long that belonged to an unknown species of sauropod – the group of long-necked plant-eaters that includes the diplodocus. The animal would have been almost 20m (65ft) long.

Dr Martill said: “Plant eaters are uncommon in this deposit, extremely rare in this region and to find one this large is very exciting. It’s a major discovery.”

Mr Ibrahim said: “Finding two specimens in one expedition is remarkable, especially as both might well represent completely new species.”

Dr Martill first attempted to reach the dig site in southeast Morocco in 1984. That expedition was driven back by sandstorms.

The expedition also involved Moroccan scientists from Hassan II University in Casablanca. Professor Samir Zouhri, of the university, said: “These fossils exceeded our expectations. It is wonderful that they will return to Morocco for display after study in Dublin.”

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