The time when the fish and sharks lived was some 330 million years ago, when what is now Scotland was located very close to the equator. The land mass was frequently inundated with warm seas which created tropical lagoons and swamps. The lagoon of interest in this area was of brackish water and extended from Ayrshire to Milton of Campsie and to the south of East Kilbride.
Marine life included fish and sharks which when they died sank into the thick muds below the equatorial waters. The mud provided an ideal environment to preserve these fish and sharks. Over many millions of years the land which is now Scotland moved north through climatic zones. Over time, the mud was turned to rock. Sea levels rose and fell as ice melted and land rebounded from the weight of the ice. The shale became exposed due to the eroding water of the Manse Burn.
The History of Scotland tells that Lewisian gneiss rocks were formed 3 billion years ago and it was not until 400 million years ago that what is now the very west parts of Scotland joined with another land mass part of which now includes the rest of Scotland and England and Wales.
At one time Scotland was joined with what is now North America in a huge land mass called Laurentia. This helps to explains why other shark fossils similar to the Bearsden Shark have been found in Lower Namurian shales of Montana, USA.
There are scientific papers which compare the different fossil sharks and the Bearsden Shark is extensively referenced.