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Dinosaurs were social animals, moving in herds, hunting in packs, but could they dance?

Hosted by: Michael Aranda

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Images:
https://www.istockphoto.com/photo/spinophorosaurus-dinosaur-travel-gm476359080-65971089
https://www.istockphoto.com/photo/dinosaur-fossils-gm147252007-7629087
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[♪ 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].