This writer is not prone to survivalist philosophies, but there is a moment, about 15 minutes into this gripping, moving documentary, when even the most liberal viewer might find themselves sympathising with the far-right’s paranoia about an over-reaching US state apparatus.

To that point, the film has been an inspiring study of fossil hunters in action. Directed with great lucidity by Todd Douglas Miller, Dinosaur 13 follows the folk from the Black Hills Institute, a private body in South Dakota, as they happen upon a near-complete Tyrannosaurus rex fossil on Native American land.

At first, all goes deliciously. They come to a financial agreement with the relevant person and set about cleaning, preserving and cataloguing their find. Then the government arrives. An eager district attorney has decided that the institute had no right to the fossil and demands that it be returned. Terrified that the find will be damaged, the staff helps the feds carry the bones and pack them safely.

Such things happen in all countries. But one suspects that in no other western democracy would the National Guard (or its equivalent) surround the building as if some revolution were about to take place. After seizing the dinosaur – named Sue after the woman who found it – the authorities start raking through the institute’s documents in search of any other felonies. The team that discovered Sue eventually find themselves in court and at least one of their number ends up in jail.

Miller does allow a few voices in from the opposition. Keith Nelson, representing a specialist branch of the Internal Revenue Service, argues the case for crusading bureaucracy with dry sincerity. But Dinosaur 13 is very much on the side of the fossil hunters caught up in a mesh more knotted than anything in the works of Kafka. They emerge as generous, funny, committed and unnecessarily forgiving. The bittersweet end does genuinely unfair things to the heart strings. Do not miss.