By now even the media (well most of it) has cottoned onto the fact that sauropods did not drag their tails along the ground like giant lizards, but instead held them off the ground behind them. Except, well, not quite always.
While sauropod footprints are common, there are the occasional set of tracks that also show a mark that is interpreted as (and can only really be) that left by a tail dragging on the ground behind. So what’s going on, is the tail up or down?
The tracks look like this one. It’s actually an ornithischian tail drag, but it’s the only image I could find (borrowed from Li et al., 2006.), still the morphology is pretty similar to the sauropod drags I’ve seen so it’ll do for now. The can be short or long (this one is obviously very long) but quite narrow and have this sinusoidal curvature which is what you’d expect from a tail that shifted from side to side as the animal walked. So if sauropods are leaving drag marks, is the tail up or down?
First off, let’s consider the frequency of these marks.These things are really quite rare, while I’m sure there’s more out there, I’ve only seen reference to a handful in the literature when there are probably hundreds of sauropod trackways out there. That’s perhaps not surprising as the average sauropod is a pretty hefty animal and is going to be leaving tracks most places it goes, and if they heavy tail is really dragging on the floor then surely the drag marks will be pretty common.
Of course they remain rare because the tail is (largely) held off the ground. In most cases, the tail never dips down to leave a mark, even in places where the substrate is very soft and would pick up traces from something very light. So the rare occasions when we do get such traces were probably from unusual circumstances such as animals with especially long tails, or those walking on a slope or something like that. The traces we do have are also very narrow, so it’s clearly the very end of the tail that’s leaving the mark and not a more proximal, wider and heavier part. Thus despite the odd trackway showing up with a tail drag mark, this really provides confirmation that the tail was held of the ground and not dragged along as used to be depicted.
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