like i said plate tectonics....The Himalyas are formed by the collision of the Indian and Eurasion landmasses which were originally separate. This collision uplifts the mountains, which is why they are still rising. From around 200 million years ago the area between the 2 separate land masses was covered by the Tethys Sea which was filling with sediments and had sea creatures which left fossils in the sedimentary rocks formed there. Around 70 million years ago the land masses collided and this started pushing up the seabed of the Tethys. Over the years a number of phases of uplift occurred with resulted in the mountain range we see today. Currently the Indian landmass is still moving north at about 2cm a year and the Himalayas are still rising at about half a cm a year. So the Fossils found in the Himalayas are those formed in the ancient sea bed of the Tethys Sea, now exposed and pushed up to form mountains.