内容摘要：Clay is a slower surface than grass, which means more rallies, more sliding and more running.

Clay is a slower surface than grass, which means more rallies, more sliding and more running.

He points to where the three horns should be at the top of the frill, but the one in the middle is missing. "All the skulls that are decently complete have a spike in that spot," he says. "But its nice little unicorn spike doesn't seem to be there."Throughout years working at the extraordinary site, the museum team has collected 8,000 dinosaur bones, and the surfaces of the lab are covered in fossils; there are bones from Pachyrhinosaurus of every size, from young to old.

Having material from so many animals allows researchers to learn about dinosaur biology, answering questions about how the species grows and the make-up of the community. They can also look at individual variations, to see how one Pachyrhinosaurus could stand out from the herd – as may be the case with Big Sam and his missing spike.All of this detailed research, in the museum and at the two sites, is helping the team to answer the vital question: how did so many animals in Pipestone Creek die at the same time?"We believe that this was a herd on a seasonal migration that got tangled up in some catastrophic event that effectively wiped out, if not the entire herd, then a good proportion of it," Prof Bamforth says.

All the evidence suggests that this catastrophic event was a flash flood - perhaps a storm over the mountains that sent an unstoppable torrent of water towards the herd, ripping trees from their roots and shifting boulders.Prof Bamforth says the Pachyrhinosaurus wouldn't have stood a chance. "These animals are not able to move very fast because of their sheer numbers, and they're very top heavy - and really not very good at swimming at all."

Rocks found at the site show the swirls of sediment from the fast-flowing water churning everything up. It's as if the destruction is frozen in time as a wave in the stone.

But this nightmare day for the dinosaurs is now a dream for palaeontologists.Canada's openness to joining the proposed Golden Dome system comes amid ongoing trade and security negotiations between the two countries, after Trump threatened steep tariffs on Canada and said it would be better off as a US state.

This galvanised a wave of national patriotism in Canada that was credited with ushering in a historic election win for Carney's Liberal government.A spokeswoman for Carney confirmed earlier that talks were due to take place on the issue.

"Canadians gave the prime minister a strong mandate to negotiate a comprehensive new security and economic relationship with the United States," said Audrey Champoux."To that end, the prime minister and his ministers are having wide-ranging and constructive discussions with their American counterparts," she said.