If paleontology serves a purpose, it is to remind us, again and again, that the current breadth of life on Earth is but a meager fraction of its former diversity. We have all, by now, become accustomed to the fleet-footed yales, the lumbering hmungos, the sumo-esque therizinosaurs, but as little as two million years ago there existed a group of herbivores completely unlike any seen today, for the most part.The eurolophs (order Eurolophia) appeared suddenly in Europe, fully diversified into a number of distinct forms, about 30 million years ago, ruled the continent through the Oligocene, and then disappeared at the end of the Pliocene. Although eurolophs are clearly ornithopods of some kind or other, the eurolophs do not fit in with any other branch of this tree. Their cranial anatomy is advanced, with a long muzzle and three rows of cheek teeth to form a "dental battery" like that of a hadrosaur. However, the jugals (cheek bones) tend to be pronounced, as in the basal ornithopods like Heterodontosaurus, and the ossified tendons that stiffened the tails and spines of every ornithopod since the Jurassic are completely absent.
From Oligocene Europe, Bavarionyx is the earliest relatively complete euroloph yet discovered. This creature is supposed to be an early rhinolophosaur, but shares some features (including its bipedal stance) with the struthiopods. Such a "missing link" may support a European origin for the eurolophs, but the evidence is still fragmentary. This is one of the most controversial fossils found in the world of Spec. Regardless of its validity at the moment, one thing is known for sure, this creature mostly like did give rise to the massive rhinolophosaurs.
The massive rhinolophosaurs of the Oligocene and Miocene were the largest of their breed, strongly convergent with hadrosaurian ungulipede . Indeed, rhinolophosaur material in France was first mistaken for very early ungulipede remains but the first complete rhinolophosaur skeleton, christened Rhinolophosaurus aumalai, was obviously not a hadrosaurian, and so the older finds, under scrutiny, turned out to be of the same stock.While the head of Rhinolophosaurus is indeed rather similar to a hadrosaur, with its battery of chewing teeth and bulbous nose, the rest of the body is not. The legs are short compared to the torso, and the neural spines over the shoulders are enlarged, traits found only in the truly huge hadrosaurs like hmungos and brutons. With such legs and spines, rhinolophs could only have been plodding, graviportal grazers, the earliest known in Eurasia. The tail, which in hadrosaurs counterbalances the body, is, as with all known rhinolophosaurs, devoid of stiffening tendons. During their time, the rhinolophosaurs were the most successful herbivores in Eurasia, overshadowing the more familiar ceratopsians and hadrosaurs for the duration of the Oligocene epoch. The Haughton impact that began the Miocene took a heavy toll on the eurolophs, drastically reducing rhinolophosaur diversity and outright killing several other euroloph clades (about which very little is known). The rhinolophosaurs came back as strong as ever in the Miocene, producing such forms as the famous Rhinolophosaurus, still the most complete rhinolophosaur material found to date. Rhinolophosaurus and its kin continued quite happily up to the end of the Miocene, but the climatic changes of the Pliocene, coupled with the influx of African ungulapeds from the south had doom for the rhinolophosaurs. While the larger rhinolophosaurus marched into extinction, the smaller eurolophs managed to escape this fate, but their numbers did suffer heavy losses as well.At the other end of the euroloph body-type spectrum are the struthiopids, known principally from the nearly complete Struthiopes from the middle Pliocene. Although these little dinosaurs are best known from fossils that are slightly younger than Rhinolophosaurus, the struthiopods are actually the more primitive of the two groups. Struthiopes probably resembled the generalized ancestor of all eurolophs.
Struthiopes and its kin were fleet-footed grazers and browsers, similar to today's oviraptor notstriches, though of a more northerly range. The forelimbs of Struthiopes were reduced to four-fingered stubs, while the hind legs were elongated and bore an enlarged middle toe that probably bore the animal's weight when running. The stabilizing tail, lacking ossified tendons, was kept rigid by the caudal vertebrae, themselves, which interlocked like the pieces of a jigsaw puzzle into a single piece.
The struthipods fared better than their rhinolophosaur cousins at the Oligocene-Miocene transition, when the Haughton Impact obliterated all large animals in the Northern Hemisphere. The bipedal eurolophs seem to have been quite common in Miocene Eurasia, but then lost ground to the hadrosaur invasion from Africa, declining through the Pliocene and finally succumbing to extinction at the onset of the Ice Age.