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[ intro ]
Though it was a contentious idea for a long
time, we know today that birds are the last
living dinosaurs.
But there seems to still be a lot of confusion
about what that means.
You might think that birds are the descendents
of dinosaurs, and that is true—
but they didn’t just appear after the other
dinos died out.
They also lived alongside them.
Think ancient egrets riding on Triceratops.
Ok, we don’t know that that was a thing,
but it’s not out of the question.
Because if you went back in time,
you would see some pretty familiar-looking
feathered animals filling many of the same
ecological roles that modern birds do today.
Archaeopteryx — that half-bird half-lizard
thing —
gave us our first clue that birds evolved
from dinosaurs all the way back in the 1860s.
But for more than a century, our actual knowledge
of what birds looked like in the Mesozoic
Era was pretty sparse.
In the past forty years, though, scientists
have unearthed all sorts of new fossils,
confirming that birds aren’t just an afterthought
of the dinosaur lineage.
And if you know anything about the paleontology
community,
you will not be surprised to hear this has
lead to some pretty heated debates—
but more on that later.
Let’s start with a very old bird: Archaeornithura.
Found in China, this bird lived over 130 million
years ago,
making it the oldest known ornithuromorph—a
grouping that includes modern birds.
Despite being only about 20 million years
younger than Archaeopteryx,
nobody would confuse this animal with a lizard.
While Archaeopteryx had a long reptilian tail,
Archaeornithura had a short little rump with
fan-shaped tail feathers, like a modern bird.
And while it still had a two tiny claws, it
also had a special set of feathers on its
wings known as alula,
which are really important for controlling
flight.
Archeopteryx could maybe fly, albeit awkwardly.
But with its new-and-improved tail and the
alula,
Archaeornithura probably had some real maneuverability
and may have flown alongside pterosaurs.
But when it came to mealtime, it was probably
a wading bird.
Most likely, it darted around shorelines looking
for small invertebrates to snack on, kind
of like sandpipers do today.
Actually, a lot of the early Mesozoic birds
that paleontologists have found probably lived
and ate near water—
though, not all.
Take, for example, a little bird called Eogranivora.
It lived in the same area of China as Archaeornithura,
though probably a few million years later.
It was also a good flier, though it likely
ran along the ground a lot—
maybe to escape from tiny Tyrannosaurus relatives.
What makes Eogranivora interesting, though,
isn’t it’s feathers or legs, but rather,
its diet.
When scientists examined the fossil,
they found what looked like seeds in its digestive
tract—the remains of the bird’s last meal.
There was evidence it had a special organ
called a gizzard
where it stored swallowed pebbles to help
it grind these up.
And that, combined with a toothless beak,
has led scientists to declare Eogranivora
the oldest known seed-eating bird.
Fossils like these have taught paleontologists
that many signature “bird” traits are
truly ancient and have occurred in lots of
divergent lineages.
Because though Eogranivora and it’s kin
looked a lot like modern birds, and they belong
to the same larger group of birds,
technically, they weren’t modern birds.
They were more like old cousins.
Modern birds all fall under the Neornithes—a
subgroup of ornithuromorphs.
And debates about when those evolved
—and whether they lived alongside dinosaurs—get
really heated.
You see, you get two very different answers
depending on how you go about trying to determine
when modern birds arose.
Molecular clocks suggest the first modern
birds appeared fairly far back—
up to 100 million years ago in the Cretaceous
Period, the last period of the Mesozoic Era.
But the fossil record for them in the Mesozoic
remained nonexistent for decades,
which suggested they only really evolved after
the dinosaurs died off.
This is often known as the “rocks versus
clocks” problem.
They named it, it’s that big of a deal.
Then, in 2005, scientists announced they’d
found something amazing: a Mesozoic duck.
Or duck-relative, at least.
Named Vegavis iaai, it was actually unearthed
in Antarctica in 1992.
And at first, paleontologists weren’t sure
what it was, but now,
they place it in Anseriformes, the order of
birds that contains ducks, geese, and swans.
It even has the oldest known syrinx, a voice-box-like
organ in birds,
which would have let it make honking or quacking
noises.
What’s really special, though, is that it
was found in a layer of rock that’s definitely,
100% pre-mass extinction.
This means when Vegavis was alive, duck-billed
dinosaurs and raptor-like dromeaosaurs
would have walked Antarctica’s beaches.
And this little duck may have had to dive
past sea monsters like plesiosaurs and mosasaurs
to get its food.
The fossil was the first solid evidence that
modern birds were already beginning to diversify
into the many different families we know today
before other dinos died out.
And now, many paleontologists think that there
were early ostrich relatives running alongside
tyrannosaurs,
ancestral chickens hiding from velociraptors,
and maybe even penguins snacking on fish!
Of course, the rocks vs. clocks problem hasn’t
been completely solved.
As you may see if there’s any paleontologists
in the comments.
There are still a lot of questions — and
arguments —
about things like how many families of birds
there were in the Cretaceous and how the mass
extinction affected them.
But the more we learn, the more it’s becoming
clear that birds aren’t just the descendants
of dinosaurs.
Millions of years before the other dinosaurs
went extinct, birds had already become diverse,
complex, and recognizable,
and they were filling some of the ecological
niches their kin do today.
So, yes, if you went back in time, you would
see some distinctly avian-looking creatures
amongst T. rex, Triceratops, and the other
famous dinosaurs.
And maybe even riding on them.
Who knows?
Outro:
For us to know what these extinct creatures
actually looked like,
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[ outro ]
