At the barest level, dinosaur bones record death and postmortem transformation. How the animal lived only becomes apparent through the clues we coax from prehistoric remains. Tracks and traces, on the other claw, are manifestations of life. Dinosaur sign, preserved as impressions in stone, record fleeting moments of anatomy in action. And within the library of fossilized behavior studied and cataloged so far, there is a small number of traces that record something that might seem unexpected within the imagery of the thoroughly modern dinosaur – tail marks.
Dinosaurs were not habitual tail-draggers. This isn’t news. In the 1970s, on the basis of anatomical and trackway evidence, paleontologists lifted the tails of dinosaurs to balance well clear of the ground. Some, such as the herbivorous, be-thumbspiked Iguanodon, had ossified tendons that added strength to a deep, rigid tail whereas the fleet carnivore Deinonychus made course corrections with the help of a tail stiffened by long, interlocking processes of the tail vertebrae.
Even without such specializations, the osteology of dinosaurs clearly testified that all the members of this celebrated evolutionary group held their tails aloft. The conspicuous rarity of sinuous drags between dinosaur footprints confirmed that dinosaurs must have held their posteriors high.
And yet, as reviewed by paleontologists Jeong Yul Kim and Martin Lockley in a new Ichnos paper, there are multiple reported cases of dinosaur tail impressions of one sort or another…