They survived intact for 112m years through scorching summer heat and freezing winters at Utah’s Mill Canyon. But several of the world’s most important and historic dinosaur footprints were damaged beyond repair earlier this year when a construction crew arrived to build a new boardwalk for tourists.

The extent of the harm to the footprints – and those of an ancient crocodile crossing in the canyon near Moab – was detailed in a Bureau of Land Management (BLM) report into the January incident published last week.

According to the bureau, the good news was that the damage was evaluated as minor, and would have been much worse if local residents had not spotted tire tracks from heavy machinery on the ground, resulting in the boardwalk project being immediately halted.

But fractures to the rims of several of the delicate prints cannot be repaired at the Mill Canyon dinosaur track site, where at least 10 species of dinosaur are known to have left more than 200 individual tracks dating to the early cretaceous period. Future freeze-thaw cycles could cause the cracks to widen, the BLM warns.

According to the report, the damage was caused by both foot traffic and construction equipment as a contractor used a digger to remove the old boardwalk at the site’s most popular area, seeking to replace it with a new, raised platform from which the public could view the tracks.

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