Complex sentence: The breed was first observed by non-Tibetans in 1995 in an isolated, long valley reached only by crossing a mountain pass, by a team of explorers led by the French ethnologist Michel Peissel.
Split into simpler sentences: The breed was discovered in 1995 in an isolated, long valley reached only by crossing a mountain pass. They were spotted by a team of explorers led by the French ethnologist Michel Peissel.