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SPEC'S LATE OLIGOCENE (c. 30,000,000 - 24,000,000 b.p.)
After millions of years of climatic seesawing, some semblance of stability had at last come to the world.
The fragments of Gondwana were now fully separated. Australia and India crawled northwards,
while Antarctica, now isolated in the extreme south, continued towards increasingly
frigidity. The climate still supported vast tracts of lush greenery, but
now there was a distinct hint of drier times to come in many parts of the
world. Here, the forests were giving way to savannah woodlands where the
recently evolved grasses were playing an increasingly prominent role.
In many ways, the dinosaur fauna of the Oligocene was the most bizarre of the entire Cenozoic. It was a
world that mixed the last survivors of relict clades with early representatives of familiar present-day
families. Many of the oldtimers were giants including the Asian lambeosaur Sauropodimimus
and the South American sauropod Acrotitan. However, these old survivors were outnumbered
by a host of weird and wonderful newer forms.
The Oligocene was the peak of protoceratopsian diversity, with the clade represented in Eurasia
and North America by everything from tiny forest runners to titanic long-necked browsers. Duckbills
of all shapes and sizes marched across North America and Africa, although they were not
very diverse in Eurasia. Here, the most common ornithopods were the eurolophs,
enigmatic creatures with no close living relatives. Strange herbivores, unrelated
to anything elsewhere, also appeared South America and Australia.
Paramegahadrus
Procurvihadrus
Titanoceratops
Bavarionychus
The carnivores seemed to also get into the spirit of weirdness. Northern tyrannosaurs sported
all manner of strange cranial crests, as did the abelisauroids of South America and Africa.
In Australia, a group of ornithopods called rhynchoraptors seized the top predatory niches,
breaking the theropod-monopoly for the first time since the Triassic.
Errosaurus
Gryphorhynchys
In terms of family-level diversity, most researchers consider the Late Oligocene
to mark the zenith of the Cenozoic dinosaur fauna. As the Oligocene drew
to a close and the Miocene began, however, this diversity began to wane.
In the oceans and throughout most of the southern landmasses, it was
business as usual (aside from unusually high planktonic turnover). However,
in a greater part of the northern hemisphere, the dinosaurs were vanishing,
losing close to one third of their species diversity.
EXTINCTION AT SPEC'S OLIGOCENE/MIOCENE TRANSITION (c. 24,000,000 - 23,000,000 bp)
The solar system is a messy place, littered with rocky and icy leftovers from its coalescence.
The Earth suffers chronic encounters with these wanderers, and while most are too small to
be of much consequence, a few, like the monster of RL's K-T, leave their scar upon both
the face of the planet and the creatures that dwell upon it. At the very
end of the Oligocene, such an event seems to have occured.
Close to 23 million years ago, a great flaming rock fell from the sky. It slammed into the arctic
and left a steaming crater 20 km across. It was not the largest object to have crossed Earth's
path, nor was the impact the only one of its time. But for life on Earth, the rock had
found the worst possible place to crash into.
The area surrounding the impact was undoubtably devastated
immediately. Thick clouds of ejecta in the air would have stalled photosynthesis
across much of the Northern Hemisphere, breaking down food chains across
North America and Eurasia and leading to the starvation of millions of animals.
As devastating as this catastrophe must have been, the scorching of the sky
was not the most serious consequence of the collision. The blast of the impact
had, after vapourising the surface sediments, encountered bedrock rich in
anhydrite (calcium sulphate) and various carbonates. Great quantities of
this material, some from over 1.7 km deep within the Earth, was thrown into
the atmosphere where it lead to an increase in greenhouse gases and deadly
falls of acid rain.
For the most part, the Southern Hemisphere seemed to escape
any serious damage, although the last of South America's sauropods vanished
at this time. Throughout North America and Eurasia, however, the dinosaurs
were in peril. In North American fossil-bearing deposits produced at that
time, one often finds as few as two or three dinosaur species where once
there were over twenty.
On the whole, larger dinosaurs were more seriously affected than smaller ones. The last of the
giant lambeosaurs along with most of the larger ceratopsians, eurolophs and neohadrosaurs vanished.
Tyrannosaurs survived as a group, but lost many of their more bizarre members.
The survivors were the errosaurs---small and generalised like the early cenoceratopsians
and megahadrids. Without competition, these little predators quickly spread
and proliferated in the Early Miocene.
On both Spec and, RL the eroded scar of the 23 million year-old impact, known as the
Haughton crater, sits in the high arctic of North America (75°22'N, 89°41'W). The
effects of the impact on RL's Cenozoic biosphere is still being investigated
and it has been implicated in a number of regional extinctions. What is certain
however, is that no megafaunal extinction event of the magnitude of Spec's
decimated northern dinosaur faunas occured in our native timeline. Why this
would be the case when all physical aspects of the impact appear identical
on both worlds is one of many issues under scientific scrutiny. One possibility
concerns the lack of insulatory structures (such as fur or feathers) on most
herbivorous dinosaurs. This may have made them more sensitive to such a sudden
large-scale climate change compared to their mammalian RL counterparts.
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