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Around 235 million years ago, all of Earth’s continents
were locked up into one supercontinent called Pangaea.
And some of the earliest known dinosaur species were roaming around, too,
but not wherever they pleased.
New research published this week in the journal Nature suggests
that these creatures started off confined to one region in southern Pangaea.
But not because of barriers like huge mountain ranges or canyons.
Instead, it was the climate that fenced these dinos in.
And it wasn’t until the climate changed that they could expand across the entire continent.
Before the rise of the dinosaurs in the Triassic Period,
Earth had gone through yet another mass extinction event.
With about 70% of all land-based species rendered extinct,
the biology of Pangaea was fairly uniform about 252 million years ago.
But as ecosystems slowly re-established themselves,
pockets of diversity started cropping up.
And around 235 million years ago,
the earliest known dinosaur species were already on the scene.
Or at least that’s what we’ve interpreted from the fossil record.
But the climate on Earth during this time was highly variable.
The concentration of carbon dioxide in the atmosphere, plus the extreme summers and winters,
divided the supercontinent into humid and dry belts.
Closer to the north or south poles, it was wet and green,
but as you moved toward the equator it became an arid desert.
And if you’re a dinosaur that thrives in a wet and green environment,
you’re probably not going to traverse that vast desert to get to the other side.
So a hypothesis arose that dinosaurs evolved on the southern half of the supercontinent,
but were not able to migrate to the rest of it until the climate changed.
But proving this hypothesis is difficult.
Dinosaur fossils from this particular point in time are few and far between,
and limited to a few spots in India and central South America.
The team of scientists behind this new research was on the case,
and they went hunting for more of these fossils in northern Zimbabwe.
Now, that might sound a little random, but before Pangea broke up into smaller continents
separated by oceans, these three locations were much closer to each other.
And, in a way, they were connected.
During the Late Triassic, the same climate belt ran through all three of these places.
And they all shared roughly the same ancient latitude…around 50 degrees South.
So the scientists went digging.
And they struck proverbial gold.
Some of the fossils they uncovered
belong to the relatives of modern-day crocodiles and mammals.
But there was also a nearly complete skeleton of an early type of dinosaur known as a sauropodomorph.
In fact, the dig revealed the oldest dinosaur fossils in Africa to date.
So it adds another dot on the map of known dinosaur locations during the Late Triassic.
But the team wasn’t done, yet.
They also tested if the Triassic climate
could restrict these early dinosaurs to this southern belt.
They created a model that took into account the changing ancient climate and the different
locations that Late Triassic and Early Jurassic dinosaur species had been found.
And their results support the hypothesis that dinosaurs did not start dispersing across
Pangea until the climate barriers relaxed.
Specifically, from about 234 to 232 million years ago, Pangaea went through the Carnian
pluvial event, when a bunch of rain caused those thick arid bands to diminish.
And it was after that time that the fossil record shows more dinosaur species being found
outside of southern Pangaea.
The model revealed that these early dinosaurs had about 5 to 7 million years to spread out,
before the climate changed again, re-building some of those barriers.
But it also predicted that two different groups of dinosaurs (the sauropodomorphs and the theropods)
dispersed at two different times.
If future dino discoveries continue to back this hypothesis up,
it could help explain the distribution of more modern species, too.
Because there were plenty of other kinds of animals kicking around back then,
including the mammalian ancestors of you and me.
And speaking of climate-influenced dinosaur discoveries, how about those dinosaur tracks
that a Texas drought uncovered last month in Dinosaur Valley State Park?
While the park is properly landlocked now, it was located beside a shallow inland sea
back when non-avian dinosaurs were stomping around.
When dinosaurs passed through the area about 113 million years ago, they left their footprints
in the mud, much like you or I would.
Except these creatures weighed upwards of 7 tons – so those tracks didn’t fill in
or wash away as easily as ours would.
Over time, some of that mud turned into stone.
The footprints were fossilized.
And the landscape changed, moving the region away from the coastline,
and adding a river, hiding the tracks away.
At least until climate change once again revealed them.
This recent drought is so severe it’s sent the water level in the Paluxy River plummeting.
Some areas have completely dried up, uncovering brand new tracks that had previously been hidden
not just by water, but under a bunch of sediment.
Now, scientists have one of the longest trails of dinosaur tracks ever discovered on their hands.
The trail includes over 60 preserved footprints the size of large dinner plates,
and most were probably made by a species of theropod called Acrocanthosaurus.
This discovery allows researchers the opportunity to learn more about this species than what
they could from just fossilized skeletons.
After all, a dinosaur’s footprints tell us more than the direction it was traveling.
They tell us if that dinosaur was traveling solo, or with a group, cluing scientists into
its social life.
And they can reveal how the species actually walked around on those two legs of theirs,
rather than trying to guess based on their bone structure.
When the drought ends, the water will hide these tracks away again.
But scientists and volunteers are hard at work to preserve what they can.
And in time, we might learn a little more about the creatures we shared this land with,
millions of years apart from one another.
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