Chenanisaurus attack?

While studying hadrosaur material from the late Maastrichtian of Aren, Spain, Caballero et al. noted pathologies in a caudal vertebra. The pathologies included anomalous bone growth, fractures and an oval hole. Noting similar pathologies in Edmontosaurus caudals, attributed by Carpenter to an attack by a T. rex, the authors considered it possible the Aren hadrosaur was bitten by a theropod. The oval hole can be interpreted as a toothmark, the fractures resulted from the impact of a bite while anomalous bone growth was due to swelling just prior to death, which occurred soon after the attack.

What kind of theropod attempted to prey on the hadrosaur? The Blasi 3 locality, which yielded the pathological specimen, also yielded teeth of dromaeosaurs and "neoceratosauria indet. of medium size."

In their paper, Caballero et al. appear to ignore the latter evidence. They assume a dromaeosaur attacked the hadrosaur, as no local theropod is considered large enough to have caused a top to bottom, i.e. attack from above, bite on the tail. This is surprising in view of the "neoceratosaurid" teeth. Spain did in fact have theropods capable of striking from above and one was almost certainly responsible for an attack. It would've made little sense for a dromeosaur to leap atop the tail and bite, as the authors suggest, when it could've more easily---and just as effectively--struck from below. 

It is true that Europe's named abelisaurs, notably Arcovenator, existed in the earlier Campanian stage. But "neoceratosaurid" teeth almost certainly indicate the presence of a coeval abelisaur. In addition, a named contemporary is known--Chenanisaurus barbaricus. This powerfully armed predator is not definitely known from Spain but it was geographically close, in nearby  North Africa, and it could have entered Europe.

Known from the late Maastrichtian of Morocco, Chenanisaurus inhabited the same environment as Ajnabia, a lambeosaurid of probable European origin. Ajnabia is related to Arenysaurus which, as the name implies, is from the exact area as the traumatized specimen. 

Clearly, there were biogeographic links between Europe and Africa, and lambeosaurs were far from the only taxa capable of migrating. Abelisaurs such as Arcovenator also moved north. Chenanisaurus could also have spread.

The short, deep jaws of Chenanisaurus, with anterior teeth D-shaped in cross section, suggest great bite force and penetrating power. The abelisaur appears to have evolved to hunt the toughest prey, which in its environment were titanosaurs. Powerful jaws and teeth enabled C. barbaricus to rip through titanosaur hides and osteoderms. This did not, however, preclude predation on hadrosaurs. Tyrannosaurus rex was also powerfully armed yet it hunted hadrosaurs as well as titanosaurs and ceratopsids. Therefore, Chenanisaurus may have caused the Aren pathologies.

The caudal wound from Aren, like those from North America, argues for attempted predation by a large theropod instead of a small one. Unable to combat a big abelisaur, the Aren hadrosaur attempted to flee (whereas it could've stood its ground and fought a small attacker) and was bitten in the tail by the pursuing predator. No doubt, the deadly Chenanisaurus could've struck with enough force to cause the observed fractures, whereas a small theropod probably could not have.

Restoration of Chenanisaurus

Reference

Cabellero, Azana, Canudo  Possible Theropod Predation Evidence in hadrosaurid dinosaurs from the upper Maastrichtian (Upper Cretaceous) of Aren (Huesca) Spain. Kaupia 2005