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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.
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.
Faced with this weird melange of characters, paleontologists can only shake their heads and tentatively
draw connections between the eurolophs and the antarctornithopods of South America and Australia. According
to this theory the eurolophs are antarctornithopods (and aberrant
even for this already bizarre group of creatures) that split off early from the rest of their kin, and rafted
to Eurasia on the Indian subcontinent as it broke from Gondwana and slid northward. This theory does explain
the sudden appearance of eurolophs, fully diversified, in the Northern Hemisphere in the early Oligocene,
but leaves many questions unanswered. For instance, why are there no decent euroloph fossils from India?
Another theory has it that the eurolophs are actually descendants of basal European
ornithopods that evolved in isolation on the island of Europe when it was separated from Asia by the Tethys
sea. This second theory's principal flaw is the lack of any undisputed euroloph material in Europe (or anywhere)
before the early Oligocene, and one would expect to find Eocene eurolophs of some form or another in Europe
if this theory were true. Absence of evidence is not evidence of absence, however, and it may be that we just
haven't been looking in the right places.
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.
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The massive rhinolophosaurs of the Oligocene and Miocene were the largest of their breed, strongly convergent
with hadrosaurian ungulapeds. Indeed, rhinolophosaur material in France was first
mistaken for very early ungulaped remains but the first complete rhinolophosaur skeleton, christened
Rhinolophosaurus, 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 eurolophs, 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 spelt doom
for the rhinolophosaurs.
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
nostriches, 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.
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