These rather adorable footprints - with a little chalk enhancement to make them more visible - were left by a group of small dinosaurs, revealing the ancient "road" they traveled all those millions of years ago.
This is a fairly unique find - we do occasionally find dinosaur footprints, but usually just those of a single individual. Here, we have evidence of a herd. Even better, this appears to be a trackway, meaning this was a path along which these dinosaurs frequently traveled. That allows us rare, if limited, insight into the behavior and social life of these ancient creatures. Here we can see evidence of six distinct dinosaurs traveling in the same direction, which is a very good indication that we're looking at a full-fledged herd here, something that's very difficult to find evidence of otherwise.
We can't know from just footprints what sort of dinosaur they belonged to. But Brian Switek over at Dinosaur Tracking breaks down the most likely possibilities:
In this case, sauropods are the best fit for the kidney-shaped tracks left by the front feet and the roughly triangular prints left by the hind feet, especially given their distance from one another. What kind of sauropods left the tracks? That's difficult to say, but Castanera and co-authors propose that small titanosaurs might be the best fit. This widespread sauropod group-which included the gargantuan Argentinosaurus and the dwarf genus Magyarosaurus-was partly characterized by having wide chests, which gave their trackways a "wide gauge"-or a wider gap between the left and right limbs-that matches the pattern seen in the Teruel tracks. The problem is that the bones of titanosaurs are virtually unknown from the appropriate place and time period, so the trackways could have been left by another sort of sauropod which moved in a similar way.
For more, check out the rest of his post. You can also see the original paper at Palaeogeography, Palaeoclimatology, Palaeoecology.