[♪ INTRO]
It probably doesn’t surprise you to hear that dinosaurs were social animals.
After all, when you see them in movies, TV, and documentaries, they’re often
migrating in herds, raising families, and hunting in well-coordinated packs.
But you might be wondering how paleontologists figure out
how dinosaurs behaved.
I mean, once they become fossils, they stop… behaving.
Interpreting behavior from fossil remains is possible, but it’s tricky.
And while some common conceptions about dinosaur social lives are supported by
good evidence, other popular ideas aren’t quite as set in stone as you might think.
When it comes to studying creatures that lived about 245 to 65 million years ago,
even the most basic questions can be hard to answer.
Like, whether dinosaurs that are buried together actually lived together.
If you find a bunch of dino skeletons in the same place, you might think the species
lived in a herd and died as a group.
But maybe they just happened to die in the same spot.
Or maybe they died in
totally different places, and their bodies were washed to that same spot by a river.
With so many possibilities, it can be tough to tell a crowd from a coincidence.
To sort out this problem, paleontologists turn to taphonomy, the study of how
ancient life becomes buried and fossilized.
For example, a 2008 study examined about 13 small bipedal dinosaurs called
Sinornithomimus that were found buried together in Inner Mongolia.
By carefully studying this site and its fossils, the scientists found enough
taphonomic evidence to determine that this was a fossilized herd of dinosaurs.
For one thing, the skeletons don’t show many signs of
having been moved after death.
Also, the legs and tails had sunk through the layers of ancient lake mud.
Those are signs that the dinos died on the spot,
probably by getting mired in the muck.
On top of that, the skeletons were arranged close to each other,
and fossilized in a similar condition and orientation.
Plus, they were buried along the same ancient mud layers.
These are all signs that they arrived and died together.
Similar group burials point to possible herd behavior in lots of dinosaurs,
like horned ceratopsians, long-necked sauropods,
meat-eating theropods, and many more.
But body fossils like skeletons aren’t our only evidence for dinosaur herds.
We also have trace fossil evidence from footprints.
A line of footprints is called a trackway, and multiple fossil trackways in one spot
can mean a march of many dinosaurs.
But just like with skeletons, there are other possibilities.
Maybe multiple dinos walked by at different times.
And again, astute paleontologists can look for clues to work out whether a set of
trackways was made by a dino community.
For example, if a group of dinosaurs were walking together, we would expect the
trackways to lie beside each other along the same path
instead of criss-crossing in multiple directions.
We’d also expect the tracks to be preserved in the same layer of ancient sediment.
Paleontologists can even examine the patterns of footprints and estimate if the
dinos were walking at similar speeds and coordinating their movement.
And in fact, we see trackways like this all over the world, showing that many
dinosaurs moved in herds.
We not only have clues that dinosaurs were social, we also have fossil evidence of
a very specific group behavior: parental care.
At one Chinese site, fossils of small dinosaurs called Psittacosaurus were found
buried in large groups including 34 young individuals alongside one adult.
At another site in Montana, paleontologists found one adult and two young
skeletons of Oryctodromeus buried together inside a collapsed burrow.
Across Asia, there are several known examples of oviraptorosaur skeletons
fossilized on top of nests filled with eggs.
And the dinos’ legs are tucked under their bodies just like a brooding chicken.
In one case, the brooding dinosaur’s eggs contained fossilized embryos
that were nearly ready to hatch.
That means the adult dino didn’t just die while laying the eggs,
but seems to have tended the nest while the eggs developed.
Finds like these are good evidence that some dinosaurs weren’t just social,
they were also good parents.
And sometimes it took a village to raise a dino child.
A 2019 study examined a site in Mongolia’s Gobi Desert where at least 15 fossil
dinosaur nests were buried close together and sandwiched
between the same ancient sediment layers.
This appears to be a communal nesting site, where multiple dinosaurs made nests
together, just like many birds do today.
And in the United States, the dinosaur Maiasaura,
whose name means “good mother lizard,”
has been found in fossil assemblages
that include multiple adults, young, and nests.
These incredible fossil finds are solid evidence that at least some dinosaurs moved
in herds, raised their young, and even gathered together in dino nurseries.
But other social behaviors can be tougher to figure out,
even when we know they must have happened.
Like, we know a dinosaur can’t raise babies without first having babies,
and for that, it needs a mate.
Courtship rituals are common among animals today.
And our modern-day dinosaurs, birds, are champions at it.
Ancient dinosaurs must have attracted mates somehow.
But finding behavioral evidence in fossils isn’t easy.
So paleontologists often look for clues on the dinosaurs’ bodies.
Lots of dinosaurs have elaborate structures that might have been used for sexy
mating displays, including horns, head crests, and feathers.
But there’s been a lot of debate over how to tell if a flashy body part is suited for
sex or for something else.
Take the frills and horns of Triceratops.
These could easily have been used for displaying to the opposite sex or for fighting
rivals over mating rights, similar to the way elk or moose use their antlers.
But on the other hand, maybe their purpose was defense against predators.
Or it might have been Cretaceous climate control.
All that surface area would have been great for absorbing or releasing extra heat.
Or, just to make things really complicated,
they could have served all those functions… or none of them.
And the dinosaur world was full of strange structures like these:
the head crests of Parasaurolophus, the back plates of Stegosaurus,
the sail of Spinosaurus.
It might be impossible to tell for sure what function these features served.
But there are some clues we can look for to determine whether
dinos were using body flair to seduce their mates.
Sexual display structures in modern-day animals follow some typical patterns.
Often, they don’t develop fully until adulthood.
Sometimes they’re different between males and females.
And they’re often expensive, meaning they use lots of energy to grow and
maintain, and might even get in the way.
Think of the unwieldy feathers of a peacock’s tail.
And there are some cases among dinosaurs that seem to fit the bill.
The small Caudipteryx had long showy tail feathers not unlike a peacock.
And Triceratops’ headgear does change quite a bit
as it matures from youth to adulthood.
But there’s still plenty of debate over these features,
and we may never know exactly how these dinosaurs were wooing their partners.
If only courtship could leave other fossil evidence!
Well, maybe it can.
A 2016 study identified several cases of dinosaur footprints
alongside unusual scraping marks.
These gouges in the ground seem to have been made by
a large predatory dinosaur.
And the study authors point out that the scrapes are similar to ones
made by birds like puffins.
Male puffins do foot-sliding and stomping dances to show off for females.
So this could be a dino dance floor!
But as you can probably guess by now, there are other explanations to consider.
Maybe these scrapes are signs of nest-building or territory-marking.
So, while the study authors favor their dancing dino hypothesis,
not everyone is convinced just yet.
As we’ve seen, some dinosaur social behaviors have lots of evidence
to back them up, like herding and parenting.
Others are strongly suspected but hard to prove, like courtship.
And then there are some ideas that are really popular but
not as well-supported as they seem.
Take pack hunting.
Movies, video games, and news headlines love to portray predatory dinosaurs
hunting cooperatively like wolves.
And this idea has a long history.
One of the most famous dinosaurs suspected of pack-hunting is a wolf-sized
North American carnivore called Deinonychus.
Deinonychus had a body built for hunting.
And in many fossil sites, numerous Deinonychus skeletons and teeth are found
alongside the remains of a cow-sized herbivorous dinosaur called Tenontosaurus.
Some paleontologists wonder if such sites could be evidence that these intelligent,
nimble predators worked together to take down larger prey, leaving behind lost
teeth and mortally wounded pack members to be
fossilized alongside the dead herbivore.
This idea has become really prominent in pop culture.
In Jurassic Park, the movies’ version of Velociraptors,
a close relative of Deinonychus, are portrayed as super-smart team predators.
But some experts argue that the evidence doesn’t hold up.
They point out that even if these predators were eating together,
that doesn’t mean they hunted together.
Today, Nile crocodiles often hunt in the same spot,
and they even help each other tear apart food.
Likewise, Komodo dragons and vultures are both known to
gather in groups around dead or dying prey.
But none of these animals hunt in packs like wolves.
In fact, sometimes they don’t get along at all.
And that might have been the case for Deinonychus, too.
At those supposed kill sites, injuries on Deinonychus bones might be signs that
these predators were attacking and possibly even eating each other.
If so, that seems less like a pack of wolves sharing their food, and more like a
hungry group of crocs or Komodo dragons barely tolerating each other
while they grab what meat they can.
Also, a study in 2020 examined some Deinonychus teeth.
Specifically, chemical signals that are affected by the type of food the animals ate.
And it found that adults and juveniles likely had different diets,
which suggests they weren’t sharing food.
Because that doesn’t match up with wolf packs,
in which everyone who’s old enough for solid food shares in the spoils.
So, pack-hunting in dinosaurs is a really cool idea,
and it’s totally possible some of them did it.
But it’s really tough to show for sure from fossil evidence.
There’s plenty of evidence that some predatory dinosaurs might have lived in
groups, including smaller dinos like Deinonychus and even
huge carnivores like tyrannosaurs.
But animals that live or travel together don’t necessarily hunt together, and finding
solid evidence of cooperative hunting in dinosaurs has proven tricky.
Like sexual signaling, this is one of those behaviors that
we might never be able to confirm.
On the other hand, maybe there’s some undeniable evidence still out there
waiting to be recognized.
As you can see, understanding dinosaur behavior can be tough, and
paleontologists have to be critical of their evidence.
But the more researchers discover exceptional fossil remains, and the more they
come up with clever new techniques for answering questions, the more we’ll be
able to learn about the long-lost social lives of dinosaurs.
Thanks for walking the dinosaur with us today!
If you’d like to help us make more great videos like this one, well, you can.
Check out patreon.com/scishow to learn more,
and if you’re already a patron, hey, thanks.
[♪ OUTRO]