North America

North AmericaSeason 2, Episode 5
Air date	May 26, 2023
Director	Andrew R. Jones
Previous	Oceans

“ Not many can intimidate North America's top predator, T. rex, whose size and bite are a deadly combo, except for a giant winged foe. ”

― The official Apple TV+ episode synopsis for North America

North America is the fifth and final episode of the second season of Prehistoric Planet, and the tenth episode of the series overall.

Segment I: The Javelina Shoreline

	North America, Segment I
	Setting Javelina Formation, Texas, USA Filming Location Wharariki Beach, Cape Farewell, South Island, New Zealand

North America, Segment I

Setting
Javelina Formation, Texas, USA

Filming Location
Wharariki Beach, Cape Farewell, South Island, New Zealand

Alamosaurus herd traveling down the shores of the Western Interior Seaway

“ The coast of the vast, inland sea that almost splits North America in half. Here in the south, as the tide falls, giants are drawn to the shoreline. These Alamosaurs are a hundred feet long, and weigh some 80 tonnes. They are the largest dinosaurs on the continent. So huge that no predator can tackle them. ”

― David Attenborough, North America

In the first segment of the episode, by the shores of the Western Interior Seaway, a herd of Alamosaurus travel along a beach. Given their great size, the titanosaurs are able to travel without fear of harm from any predator.

The 70 year-old Alamosaurus collapses

“ Some live to a great age. This male is around 70 years old. Many in the herd are likely to be his offspring. But his long life is now coming to an end. His immense body is beginning to fail him. He may not survive the night. ”

― David Attenborough, North America

As they go around a bend in the path, one 70 year-old male, feeling that his time is up, slowly drops down on the beach, the rest of the herd moving on without him. Accepting that his long life is at its end, the old male lays his head on the sand, closes his eyes, and peacefully passes away.

Troodontids assess the Alamosaurus carcass

“ Dawn. And these troodontids have picked up a scent. They're quick to investigate anything new, especially if it might be worth eating. But biting through a three inch-thick hide is beyond their power. Very frustrating. ”

― David Attenborough, North America

The next day, a trio of troodontids visit the beach, having smelled the corpse of the recently-deceased titanosaur. Skittishly, they explore and climb atop the dead sauropod, looking for the best part to start their meal. To their frustration, however, the small theropods found themselves unable to bite through the titanosaur's hide, which is three inches thick.

A T. rex forces a troodontid away from the Alamosaurus carcass

“ Tyrannosaurus rex. North America's top predator. With his six inch-long teeth, tearing through an Alamosaur's tough skin is not a problem. ”

― David Attenborough, North America

As they continued to attempt to take bites out of the corpse, the troodontids are then scared away by a male Tyrannosaurus, which is easily able to feed on the carcass with his six-inch teeth and bone-crushing bite. One troodontid manages to take one strip of meat as the T. rex feeds before being forced away again.

“ T. rex might be able to bully troodontids, but a carcass as big as this soon attracts more formidable competition... ”

― David Attenborough, North America

The smell of the massive carcass, extremely visible on the open beach, soon attracts the attention of other carnivores. As he is eating his meal, the T. rex soon hears a series of booming calls from above, and turns towards the source of the noise, growling in frustration upon realizing that he can no longer eat the carcass undisturbed.

A T. rex stands against a Quetzalcoatlus wanting to drive him away from the dead Alamosaurus

“ Quetzalcoatlus, a giant pterosaur. One of the few creatures that will challenge an adult tyrannosaur. One strike from its six foot-long beak could easily cost T. rex an eye. Even so, it seems that he's not going to back down. ”

― David Attenborough, North America

A Quetzalcoatlus lands down on the beach, eyeing the dead titanosaur right in front of it. The T. rex roars at the Quetzalcoatlus in an attempt to scare it off, but the azhdarchid pays no heed to the theropod's warnings as it slowly marches towards the carcass. The T. rex turns to face the pterosaur, revealing that his right eye is milky, with a horizontal scar across the eyeball, implied by the narration to have been rendered blind by a prior Quetzalcoatlus attack. As the T. rex continued to growl at it, the azhdarchid paused its advance to test the extent of the T. rex's aggression. Believing that his taller, lankier rival would not attempt to challenge him further than it already has, the T. rex turns back to his meal, prompting the Quetzalcoatlus to try and walk towards the carcass again.

The second Quetzalcoatlus bellows at the T. rex

“ But the arrival of a second Quetzalcoatlus changes the odds. After all, two beaks are deadlier than one. ”

― David Attenborough, North America

No sooner did the theropod return to eating than another bellow echoed from the skies. Both the T. rex and the Quetzalcoatlus paused to turn their attention to the new arrival. A second Quetzalcoatlus has landed on the beach, and together, the two pterosaurs boldly close in on the T. rex.

The two Quetzalcoatlus goad and provoke the T. rex to try and chase them off

Both Quetzalcoatlus charge in, snapping their beaks to make clear their defiance, but quickly dart away as the aggravated T. rex rushed towards them. Their intent is not to take on their heavier and more powerful adversary head-on, however. Instead, they plan to repeatedly harass and even injure him until they had inflicted enough discomfort to convince him to leave. While one Quetzalcoatlus gets chased off by the T. rex, the other lands atop the Alamosaurus corpse, diverting the T. rex's attention and enraging him even further.

The Quetzalcoatlus assault the T. rex from above and behind

As this azhdarchid gets into a squabbling match with the T. rex, having the annoyed theropod's undivided attention, the other Quetzalcoatlus flies at the T. rex from behind, almost pecking him in the back as it passed overhead. With the T. rex distracted yet again, the other Quetzalcoatlus leaps off the dead Alamosaurus to take part in the aerial harassment. Again and again, the two Quetzalcoatlus strike the T. rex in the back with their long beaks as he tried to swing around and grab one of them.

The victorious pair of Quetzalcoatlus scavenge the dead Alamosaurus

“ For T. rex, this is now too dangerous. Some fights just aren't worth the risk. For now, the flying giants have won. They quickly eat all they can. But T. rex will almost certainly be back to claim his share once his flying rivals leave. ”

― David Attenborough, North America

Overwhelmed by the assault, the T. rex, unwilling to risk receiving potentially more grievous injuries, abandons the titanosaur corpse to the azhdarchids, whom promptly feast on the bountiful meal. Given how the Quetzalcoatlus pair are unlikely to strip a considerable amount of the massive carcass clean, the T. rex will almost certainly return to feast on what is left once the pterosaurs have had their fill and moved on.

Segment II: Globidens and Sphenodiscus

	North America, Segment II
	Setting Gulf of Mexico, Western Interior Seaway, USA

North America, Segment II

Setting
Gulf of Mexico, Western Interior Seaway, USA

“ In the waters that surround North America, there are other giant predators. But they have no rivals. Mosasaurs. They may look like huge sharks, but they are in fact, a kind of aquatic lizard. Size, speed, and powerful jaws mean that very few creatures in the ocean are safe from these hunters. In the Gulf of Mexico, this Globidens mosasaur is searching for one particular kind of prey. ”

― David Attenborough, North America

In the second segment of the episode takes place in the Gulf of Mexico, where a Globidens swims through the open seas, seeking out shoals of its favorite prey, "tiger ammonites".

“ Tiger ammonites, Sphenodiscus. Every year, huge shoals of females come up from deep water, and travel towards the coast. They have all recently mated, and each is now carrying hundreds of fertilized eggs. The eggs must be laid in the shallows... and that is where the mosasaur is waiting. ”

― David Attenborough, North America

Every year, from the deep levels of the ocean, thousands of female Sphenodiscus come up to the coast, each ammonite carrying hundreds of fertilized eggs that need to be laid in the shallows, right where Globidens is waiting for them, using its forked tongue to hone in on their location.

Globidens pursues a Sphenodiscus

“ Tiger ammonites are themselves hunters. The combination of a streamlined profile and a powerful siphon enables them to shoot through water at great speed. But so can the mosasaur. ”

― David Attenborough, North America

The Sphenodiscus use their own predatory traits (their streamlined profile and powerful siphon) to get to their destination faster and evade incoming threats. Unfortunately for them, Globidens is also quick enough to catch up to them and attack.

“ Globidens has broad, rounded teeth that easily crack the ammonite's shell, releasing the air that keeps them buoyant. Without it, they sink helplessly to the seabed. Before the ammonites can escape, the mosasaur disables as many as it can. ”

― David Attenborough, North America

With its globular teeth, the mosasaur easily crunches through the shells of the ammonites, releasing the buoyant air within its prey, disabling and sinking as many Sphenodiscus as it can instead of taking time to consume each ammonite it catches. Once the shoals of ammonites have passed through the area, with no more prey to cripple, Globidens feeds on the ammonites it sunk to the ocean floor, cracking the dead open with its teeth before ripping out their soft bodies from their shells.

Globidens rips a Sphenodiscus out of its shell

“ Finally, time to tuck in. Globidens may have killed dozens... but even this makes only a small impact on the overall numbers of ammonites. Most of the shoal have survived, and continue on their journey to their spawning grounds. The rocky seabed here has many cracks and crevices, ideal places for attaching the ammonites' precious egg sacs. The females then abandon them. But safe in this coastal nursery, these eggs will produce the next generation. These coastal seas are full of life... ”

― David Attenborough, North America

Despite the mosasaur having killed dozens of the ammonites, hundreds more make it to the shallows to successfully lay their eggs. The females deposit their egg sacs in the many rocky crevices in the seabed, and leave them. Safe in the coastal nursery, the eggs will spawn the next generation of ammonites to continue the cycle.

Segment III: Pectinodon and "Styginetta"

	North America, Segment III
	Setting Denver Formation, Colorado, USA Filming Location Mono Lake, Mono County, California

North America, Segment III

Setting
Denver Formation, Colorado, USA

Filming Location
Mono Lake, Mono County, California

“ ... yet on land, and only a few hundred miles away, there is desolation. Here, powerful movements deep in the Earth's crust are beginning to raise the Rocky Mountains. The immense changes in the landscape have cut off this lake from nearby rivers. Its waters evaporate in the strong winds and intense summer sun, and the minerals that have dissolved in it are beginning to reach toxic levels. For most, this water is simply too poisonous to drink. Even so, every year, this place is visited by all kinds of animals. ”

― David Attenborough, North America

In the third segment of the episode, many animals are shown visiting an evaporating toxic lake for feeding opportunities. Among them, "Styginetta", a primitive relative of ducks, and a family of non-avian dinosaurs. Six juvenile Pectinodon poke out from the rocks, lead to the toxic lake by their father.

“ These dinosaurs and the Styginetta are both drawn here by a strange seasonal bonanza. Flies. The larvae of these insects are able to filter out the lake's toxic salts, and, as a consequence, they thrive in immense numbers. Now, they're hatching into adults in their millions. They are a rich and abundant source of protein for all the lake's visitors. Pectinodon are particularly intelligent dinosaurs. It doesn't take them long to work out the best way to collect flies. ”

― David Attenborough, North America

Watching millions of flies and emerging from the lake, the juvenile Pectinodon jump up and snap at the flies, but they soon eventually figure out that the best way to scoop up as many flies as possible is by rushing at them, stirring the flies like dirt from the ground, with their jaws gaping open to collect them in mouthfuls. A flock of "Styginetta" watch as the juveniles run around gulping flies, which eventually ends up with two of the juveniles crossing each other's paths while rushing, causing them to collide and get knocked to the ground.

“ But their father has his eyes on a bigger prize. Pectinodon are not only intelligent, they're also very skillful hunters. ”

― David Attenborough, North America

While all this is happening, however, the father of the Pectinodon chicks closes in on one "Styginetta" flock from behind, slowly approaching the birds while staying low, obscured by the rock and mineral pillars around the lake. By the time the birds realize he is there, the flock taking to the air, the Pectinodon leaps up and catches one by the throat in midair, swinging and slamming his prey twice to the ground before finishing off the bird with another bite.

“ Success. A rather more substantial meal for the family, and just as well. The flies will only be here for so long, and the dinosaur family will be forced to find food elsewhere. ”

― David Attenborough, North America

As the "Styginetta" fly off, with many other flocks of them still ankle-deep in the lake, looking for flies to eat, the Pectinodon father brings his catch to his six chicks, the family settling down to eat as flocks of "Styginetta" fly overhead.

Segment IV: Triceratops Gathering

	North America, Segment IV
	Setting Lance Formation, Wyoming, USA Filming Location Winterfold Forest, western Greensand Ridge, Surrey, England

North America, Segment IV

Setting
Lance Formation, Wyoming, USA

Filming Location
Winterfold Forest, western Greensand Ridge, Surrey, England

Several Triceratops gather in a forest clearing for their mating season

“ Further north, the Rocky Mountains are still slowly rising. And as they do, they create higher, cooler landscapes where vast pine forests flourish. As spring arrives, strange calls echo through the trees. The mating season has arrived for one of North America's most heavily-armed dinosaurs. Triceratops. Every year, large numbers of these giants gather in clearings. The females have come to choose a mate. The six-tonne males fight and display their strength. ”

― David Attenborough, North America

In the fourth segment of North America, in the pine forests further up north by the Rocky Mountains, strange calls echo. Within a clearing, a large number of Triceratops gather, with females looking for mates, and males fighting to prove which one of them is the better candidate.

A female (left) is unimpressed by the young male's display (which, being unscarred, indicates a lack of experience)

“ This young male looks to be in prime condition, showing off his meter-long horns and his colorful head frill. His horns appear perfect, not yet damaged by battle. To a female, however, the absence of any wear and tear might suggest a potentially-critical weakness; a lack of experience. ”

― David Attenborough, North America

One of the young, six-tonne males attempts to impress some females by showing off his colorful frill and meter-long horns, perfectly-shaped and undamaged. Ironically, for the females, this makes the male a subpar choice, for the lack of wear and tear shows that the male is inexperienced, not seasoned by battle.

The veteran male arrives to the mating grounds, making his presence known to all

“ These gatherings are crucial events in the lives of Triceratops. They provide the best chance in the whole year for the adults to become parents. And young hopefuls are not the only ones here. A 30 year-old male, weighing more than 10 tonnes. If there's one thing that he has in spades, it's decades of wear and tear. He may be old, but he's still strong enough to challenge a young rival, however fit. The stakes are high, and neither is willing to back down. ”

― David Attenborough, North America

Just then, a 30 year-old male, weighing over ten metric tons, walks in, his experience clear in his massive physique and impressively-long horns, with his right one longer than his left. Challenging each other to a duel, the younger male with the perfect horns and the veteran clash, locking horns repeatedly.

The veteran (left) uses his ten-tonne mass to push back his rival

“ The veteran has a four-tonne weight advantage... and the skill to make it count. ”

― David Attenborough, North America

Even so, it is clear that, in the struggle, the veteran has full control of the battle, using his greater mass to push the younger male back, while the younger male is unable to hold off the veteran. As they continue to lock horns, the veteran uses the skill he mastered through decades of experience to lift his rival up by the face and throw him to the ground.

The veteran successfully attracts a mate with his flawless victory

“ The youngster's horns are no longer perfect. The old bull's fighting prowess certainly seems to have impressed this female. ”

― David Attenborough, North America

When the dust settled, the younger male stood back up, the tip of his right horn snapped off and on the ground, along with his aspirations of getting a mate. The veteran proceeds to drive him off before attracting and mating with a female that witnessed the fight. The young male, with his horns no longer perfect, walks away, his chances for that year's mating season gone. Even so, there is the hope that, with this damage, he can attract a female next mating season, for he now has proof of having faced battle, regardless of whether it went his way or not.

The young male watches on in defeat before leaving

“ For the loser, the mating season is over. However, his newly-won battle scars may be just enough to attract a female next time the herds gather here to mate. ”

― David Attenborough, North America

It is even possible that, when he grows older and his left horn has healed, he'll end up being just like his opponent, a grizzled, ten-tonne veteran with longer horns, the right one longer than the left, a sign of great experience.

Segment V: Nanuqsaurus and Ornithomimus

	North America, Segment V
	Setting Prince Creek Formation, Alaska, USA Filming Location Meagher County, Montana, USA

North America, Segment V

Setting
Prince Creek Formation, Alaska, USA

Filming Location
Meagher County, Montana, USA

A flock of Ornithomimus run around in search of food as spring begins

“ Here, within the Arctic Circle, for three months of the year, the sun barely rises. When its warmth finally returns after the long winter, feathered Ornithomimus are quick to take advantage. These fleet-footed travelers are among the fastest runners of all dinosaurs, capable of covering vast distances in search of fresh vegetation. They're so fast, they're very difficult for predators to catch. ”

― David Attenborough, North America

In the fifth and final segment of North America, following three months of cold winter darkness, the sun finally rises and warms up the Arctic Circle. A flock of nine Ornithomimus rush out, using their great speed to cover vast distances and find fresh vegetation, eventually finding what they sought for in a thawing field of snow.

Nanuqsaurus stalks the flock of Ornithomimus

“ After a tough winter, this female Nanuqsaur needs to make a kill soon. A smaller relative of T. rex, but more agile, and, critically faster. There is nowhere to hide, so a surprise attack is impossible. Instead, she resorts to creating panic. ”

― David Attenborough, North America

A short distance behind them, a female Nanuqsaurus eyes them hungrily. With nowhere to hide and therefore no opportunity to ambush, the Nanuqsaurus decides to just outright rush at the flock and hope one blunders due to panic. The flock splits into two, four moving to the right as the other five rush left, the Nanuqsaurus choosing to continue chasing the latter group. Eventually, the Nanuqsaurus, out of energy, halts its pursuit, growling in frustration as the Ornithomimus dash further away.

A flock of Ornithomimus get away from Nanuqsaurus

“ Each failed hunt uses up more precious energy, bringing her ever closer to starvation. ”

― David Attenborough, North America

Although it was spring, the Arctic Circle was still subject to freezing winds and fluctuating temperatures. A flock of seven Ornithomimus (which may or may not involve the same individuals from the flock seen before) are out grazing on a rocky slope full of vegetation, and this time, the Nanuqsaurus takes advantage of the flurries of snow and the rocks around her to close the distance between her and the flock without being seen. Slowly, she inches forward, and charges at the flock once she was close enough. Screeching, the seven Ornithomimus rush down the slope, the tyrannosaur just a few feet behind them. Two Ornithomimus split off to the right, and the Nanuqsaurus goes after the larger group of five which ran left.

Nanuqsaurus carries her fresh kill to the top of the mountain

One Ornithomimus in the back slightly stumbles on the ground, getting left behind by the others, and, realizing that it is now the main target of the predator, circles back and runs left, back up the slope, almost getting caught by the Nanuqsaurus in the process. The pursuit continues up the mountain until eventually, the Ornithomimus makes a critical error and slips on the snowy terrain. Just before it could fully get back up, the Nanuqsaurus finally grabs it by the throat, dragging it around before crushing its neck with her jaws. Checking to see if her prey is really dead, the Nanuqsaurus picks up the freshly-slain Ornithomimus by the neck and makes a slow trip back up the mountain, where her seven hatchlings are waiting.

Nanuqsaurus tends to her chicks

“ If her babies are to thrive, she will have to repeat today's success over and over again, until her young are old enough to join her in the hunt, and, eventually fend for themselves, here in this remote - and perhaps the most challenging - frontier of the North American continent, 66 million years ago. ”

― David Attenborough, North America

As the family feeds on what may be their first meal in many weeks, three Ornithomimus feeding on vegetation watch the scene from a distance, likely fearful that they may be next. Noticing them, the Nanuqsaurus gets up and turns to face the Ornithomimuses with a huff, causing them to scamper back down the slope. Turning back to her family, she tends to her hatchlings as they chirp up at her before continuing to eat the meal with them.

Uncovered Segment I: How Did Dinosaurs Get So Big?

	How Did Dinosaurs Get So Big?
	Subject The evolutionary means and efficient systems that let sauropods attain their massive sizes. Experts Professor Paul Barrett, Dr. Susannah Maidment

How Did Dinosaurs Get So Big?

Subject
The evolutionary means and efficient systems that let sauropods attain their massive sizes.

Experts
Professor Paul Barrett, Dr. Susannah Maidment

This Uncovered segment, using footage of all of the sauropods from the first two seasons except for the Nemegt Forest Titanosaur, is dedicated to explaining how sauropods became the largest land animals to ever live, growing from eggs the size of grapefruits to titans "ten times heavier than the biggest elephant", tipping the scales at almost a hundred tons.

A giraffe and elephant compared to five dinosaurs and an azhdarchid pterosaur

In the past, strange ideas have been formulated. One such suggestion is that weaker gravity allowed for larger sizes, but gravity actually did not undergo noticeable changes during Earth's prehistory for it to matter. Another factor brought up is the oxygen level, as some studies suggested that oxygen levels during the time of the dinosaurs were around 30% compared to the modern day's 21%. While the early dinosaurs are believed to have been boosted by oxygen levels increasing compared to previous time periods, later studies estimate that oxygen levels in the past 220 million years were only around 10 - 19%, lower than oxygen levels today, and, regardless, would not have helped dinosaurs reach large sizes the same way high oxygen levels during the Carboniferous Period (above 21%) allowed insects to reach larger sizes (since, without these higher oxygen levels, insects were limited in body size due to how their respiratory system diffuses oxygen).

“ Growth patterns in fossilized bones show some sauropods got to full size in just 20 years. That's an extraordinary thousand-fold increase. ”

― David Attenborough, How Did Dinosaurs Get So Big?

Dinosaurs, not just sauropods, are believed to have grown relatively quickly for their maximum size, a trait that is seen as a sign of endothermy (the capability of an organism to generate and maintain its own body heat), which is, in turn, an indicator of the animal's efficient metabolism and active lifestyle. Some sauropods grew to full size in just 20 years, though some had even longer growth rates to attain even greater sizes, with several estimates being made due to different growth curve estimation methods and equations. For example, X-rays and CT scans indicate that Rapetosaurus grew at roughly the same rate as elephants and other modern large mammals (the fossil of a juvenile Rapetosaurus, estimated to have been 3.4 kilograms or 8.8 pounds when it hatched, grew to be around 40 kilograms or 88 pounds when it died due to malnourishment 39 - 77 days after hatching), and it may have taken Alamosaurus approximately 45 years to reach a mass of 32 metric tons (35.3 short tons), gaining a maximum of one metric ton (1.1 short tons) a year.

“ The sauropods were, to some extent, pre-adapted to be able to let them get really, really big. They had a metabolism that was probably quite like that of birds, which allows them to take oxygen on the in breath, but also on the out breath. The evidence for that is all of the holes that we see in the vertebrae and also in their limb bones. ”

― Dr. Susannah Maidment, Natural History Museum

The holes in sauropod bones contained air sacs, crucial features meant to extract oxygen in order to power their very efficient metabolism. Additionally, these air sacs and holes helped in another way. The largest land mammals are limited in size and mass by their heavy, solid bones. An African bush elephant, the largest living land mammal, has a maximum estimated weight of 10.4 metric tons (11.5 short tons), while the extinct Palaeoloxodon namadicus, believed to be the largest land mammal to ever exist, is estimated to weigh around 18 – 19 metric tons (20 – 21 short tons) according to a 2023 study. Any heavier, and the skeletons of these land mammals, comprised mostly of solid bones, would collapse due to no longer being able to support the extreme mass of their bodies. By comparison, the pneumatic, hollow, hole-riddled bones of sauropods are comparatively lighter (though overall heavier) and stronger. From natural objects like bones to manmade structures like concrete buildings and metal construction supports, holes and pores help evenly distribute forces across a material, thus lessening the concentration of stress and overall pressure. Another key feature that helped them is their posture. Like all dinosaurs, sauropods have a fully erect posture as opposed to the sprawling posture of other reptiles. With their thick, pillar-like legs positioned firmly under their bodies rather than being held out to the sides, sauropods were able to efficiently keep their weight off the ground.

“ One of the reasons why gigantic carnivores may have reached their large sizes is actually simply because they're trying to keep up. They're trying in an evolutionary arms race to stay in the game, to be able to take on some of these very large herbivores. ”

― Professor Paul Barrett, Natural History Museum

One more evolutionary factor that pushed dinosaurs to grow big is the presence of predator, prey, and competitors. Great size is a tough deterrent against more predators, and, on the other hand, could also provide more power to use against proportionally-larger prey. Great size may also allow animals to drive away their competitors, increase their feeding range for adaptability, or occupy a different niche to avoid competition. While the means and factors by which they achieved gigantism are not unique, dinosaurs proved to be among the most extreme and most successful organisms to ever rely on such methods and evolutionary paths. It is unlikely that there will ever again be such giants to walk the Earth.

Uncovered Segment II: Why Did Triceratops Have A Frill?

	Why Did Triceratops Have A Frill?
	Subject The overall function of Triceratops frills as display features and defensive weapons. Experts Professor Paul Barrett, Dr. Susannah Maidment

Why Did Triceratops Have A Frill?

Subject
The overall function of Triceratops frills as display features and defensive weapons.

Experts
Professor Paul Barrett, Dr. Susannah Maidment

This Uncovered segment, using footage of Triceratops from the second segment of Forests and the fourth segment of North America, is dedicated to uncovering the reason behind why the ceratopsian developed the head frill. Even 140 years after the first fossil was found, the purpose of the massive frill is still being investigated.

Triceratops frill scars serve as evidence of the defensive function of these structures

“ These were enormous structures, so it's an enormous investment in bone and in tissue, and also in the muscular effort to hold these structures up. All of this investment must mean that these features are very important to the animal's way of life. ”

― Professor Paul Barrett, Natural History Museum

Injuries on the fossils, like lesions on the skull and bite marks left by predators on the frill appear to indicate that they were meant for defense. But there's also the possibility that they were display structures to help attract mates. In living animals like moose, huge structures like horns and antlers serve as an attractive display and an indication of great health, which in turn helps the females know which male is ideal to mate with in order to produce the best of young.

Triceratops skulls undergo drastic changes as they grow, indicating that some features marked the animal's sexual maturity

“ If it was only for defense, then we would expect to see them develop to the same degree in juveniles as in adults, but we don't. We see them being much smaller in the juveniles and not really developing into the very, very large structures of the adults until much later. ”

― Dr. Susannah Maidment, Natural History Museum

Additional proof of their use in sexual display is seen in the very heavily-grooved surfaces of the frills, which were probably meant to house nerves and blood vessels to supply the skin growing over the frills, with these large surface areas likely being brightly colored to show off to potential mates. As a structure that serves many purposes, from attacking and defending against predators and rival males to serving as a vibrant display to attract females, the frill of Triceratops would have been an "awe-inspiring sight, to friend or foe".

Fauna

Alamosaurus sanjuanensis

Texan Troodontid

Tyrannosaurus rex

Quetzalcoatlus northropi

Globidens alabamaensis

Sphenodiscus sp.

"Styginetta lofgreni"

Pectinodon bakkeri

Triceratops horridus

Ornithomimus sp.

Nanuqsaurus hoglundi

Trivia

• This is the first (and so far only) episode in the main series to not be named after a type of environment, biome, landscape, or feature, instead being named after a continent.
• The first segment of the episode took 600 days to animate.