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(dinosaur growling)

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(suspenseful music)

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(explosions)

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Dinosaurs embody the extreme

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in just about every possible way, their size,

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power, even the long-ago time in which they lived.

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It's no wonder, the more we learn about them,

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the more they continue to captivate us.

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I think that most people have an inherent fascination

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with animals and with the natural world,

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and dinosaurs are animals and the natural world

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on the grandest of scales.

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I think it's imagining living on our earth

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when earth was a completely different place filled

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with fantastical beasts that really ignites the imagination.

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They're like dragons or other mythological creatures

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but they were real, and that's part of the appeal.

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They were a real thing.

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They are awe inspiring.

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Just take T. rex.

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T. rex is a killer whale-sized animal walking around

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on these giant chicken legs.

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You can't really compare anything alive

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to a T. rex.

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We know when the reign of the T. rex ended.

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In the calamitous dinosaur extinction event

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65 million years ago, the result

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of a massive meteor crash in the Yucatan Peninsula.

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But how did its rule begin?

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Scientists have long sought to learn more

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about the early lineage of the king

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of the tyrant dinosaurs.

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Where and when can find the roots of its family tree?

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Now, new discoveries, as well as new analysis

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of old finds are beginning to fill in the timeline.

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Almost all we know about Tyrannosaur evolution comes

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from the final 15 million year of the Cretaceous

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leading up to the great T. rex.

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There's been this huge gap, 70 million years

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in the fossil record prior to that

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where we've had no fossil evidence

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of what types of Tyrannosaurs were living here,

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so we really had not pieced together the first three

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quarters of the story of tyrannosaur evolution

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here in North America.

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Lindsay Zanno is the head

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of paleontology at the North Carolina Museum

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of Natural History.

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For more than 10 years now, she's led research teams

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to a remote part of central Utah following a trail

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of small ancient Tyrannosaur teeth on the hunt

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for something more.

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(laughing)

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You guys, you're really helping.

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It's exciting to be part of the discovery.

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I think that's my favorite part of the scientific process

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and when we're out in the field, we come across things

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we never expected to find that can define our research

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for years to come.

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And that's just what happened in 2012.

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All right, so this is the upper leg bone.

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When they found the puzzle pieces

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to a new species of dinosaur, something very different

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than anything they'd seen before.

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The knee would have been here, and this is the

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lower leg bone.

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You can see where cut a section out

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to study those growth lines.

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It was amazing.

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The first part we saw sticking out of the hill

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was this bone and these pieces here are different colors

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because we actually found each one of these

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individual pieces trailing down the hill,

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collected them all, and then the preparation teams

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spent hundreds of hours piecing together each one

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of these little bits that we had collected

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from the side of the hill.

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After the painstaking excavation,

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cleaning and assembly work, the team concluded

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this leg belonged to a small, at most

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about 180-pound animal, similar to older tyrannosaur fossils

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found in Asia, hinting at a continental migration

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to North America.

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It's a very petite animal.

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It would have been about human size.

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So when this animal was standing next to you,

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he probably would have been able to look you

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right in the eyes.

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And the tissue between is pretty consistent.

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Zanno examined cross sections

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of the fossilized bone to determine the specimen's age,

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about seven at the time of death.

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Just like counting the growth rings you'd find in a tree.

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Its growth seemed to be slowing, so it was actually

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approaching its adult body size when it died.

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So this actually wasn't just a young Tyrannosaur

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of a big species.

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This was actually a tiny Tyrannosaur.

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Seven years old when it died perhaps.

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But a fossil that's now 96 million years old

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and begins to fill in a 70-million year gap

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in the fossil record of North American Tyrannosaurs.

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Zanno published her findings in February, 2019.

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I chose the name Moros intrepidus

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just to represent that this is really the origin story

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of the T. rex lineage here in North America.

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Moros means the harbinger of doom, and T. rex

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is definitely the doom bringer, so it all made sense.

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On the dinosaur timeline, small Moros lands

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in the mid Cretaceous period, while the enormous T. rex

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lived during the late Cretaceous.

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With 30 million years in between, what suggests

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they're closely related?

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An evolutionary adaption not present

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in those early Asian relatives, a specialized foot.

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One of the things that makes Tyrannosaurs so special

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is they have a very unique foot.

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It's very pinched and it's designed for running

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and also being very agile.

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So these were incredible hunters that were able

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to chase down prey.

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Moros is the earliest example of those special

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tyrannosaur adaptations that we found

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in the fossil record.

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So somewhat like a T. rex is small, fast tyrant dinosaur

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grown huge, not a big, fat tyrant dinosaur

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that then was evolving a few new traits

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to make it go a little faster.

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Professor Thomas Holtz is a paleontologist

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at the University of Maryland specializing in Tyrannosaurs.

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He was part of the peer review for Zanno's paper.

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And with that adaptation, when they got the chance,

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Tyrannosaurs could become the fastest-moving

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large predators of all time.

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But they acquired it when they were still little guys,

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and they were probably using that fast-running foot

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as much to get away from being eaten

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as to chase things to eat.

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That's because during its time,

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small Moros was not the apex predator.

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(dinosaurs roaring)

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This lush world belonged to the much larger Allosaurus.

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Somehow though, the Allosaurus disappear,

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perhaps victims of a changing environment

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leaving Moros and its Tyrannosaur descendants

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a void to fill.

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And so likely as soon as their major competitors

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were out of the scene, they were able

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to seize that opportunity, increase in size really quickly

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and take over as the top predators

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of these new ecosystems.

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But what drove the Tyrannosaur's

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exponential growth remains a mystery.

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From Moros weighing in at 180 pounds,

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to the T. rex known as Scotty, now considered

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the largest T. rex ever discovered, tipping the scales

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at more than 19,500 pounds.

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Why Tyrannosaurs evolved to to be so big is still

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a huge paleontological question.

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Tyrannosaurus rex pushes the boundaries

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of any big carnivores that we know about.

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Scott Persons investigates those boundaries.

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A research fellow at the University of Alberta,

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he's also lead author on a new study

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about the dinosaur, Scotty, fossils found in the Badlands

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of Saskatchewan in 1991.

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But its skeletal assembly was only just installed

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for display at the Royal Saskatchewan Museum in May, 2019.

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Scotty earned its name because shortly after

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it was discovered, the field crew got really, really excited

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and they wanted that evening to raise a glass

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to Tyrannosaurus rex, to toast the tyrant king.

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And the only bottle that they had on hand

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that seemed appropriate was a very old bottle of scotch.

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I became involved in researching Scotty

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only about two years ago.

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That was after the fossils were fully excavated

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and fully prepared, so they were ready for scientific study.

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The team at the Royal Saskatchewan Museum

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used laser scanners to create 3D images of the bones.

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Now almost 30 years after the initial discovery,

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Persons's new analysis revealed Scotty

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to be the T. rex ever found, dethroning Sue

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from the Chicago Field Museum.

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We say Scotty is the biggest in terms

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of its absolute body mass.

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So those skeletal measurements that indicate

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just how much the animal would have weighted

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suggest that Scotty is the most massive.

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And when you look at things like the girth

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of the femur, so the femoral circumference,

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when you look at the length of the lower jaw,

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when you look at even the thickness of the shoulder,

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Scotty comes out ahead.

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Thomas Holtz also peer reviewed

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Persons's paper.

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And honest to goodness, we can't say that Scotty,

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on the lean season, when there's not much food,

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and Sue in the season when there's a lot of food,

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Sue may have been heavier some times of the year,

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and Scotty heavier some of the other times of the year.

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But overall the evidence is, on average, Scotty

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is a larger individual than Sue.

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And Sue is already a really, really, really

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massive individual.

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So Scotty is the rex of rex's.

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It's the king of the Tyrannosaurs.

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An estimated 30 years old

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at the time of death, Scotty is also the oldest

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T. rex ever found.

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In a world where Scotty and the other big animals

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are around, are only living to about 30 years old,

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it's telling us there's a lot of turnover going.

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There's a lot of individuals changing over

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in the population.

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As I like to say, in the Mesozoic, life was cheap.

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Scotty shows evidence of a busted

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and then infected jaw.

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Its got several broken and healed ribs.

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Its also got a number of vertebrae in the tail

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that shows signs of very strong compression

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and that may be indicative of a place

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where Scotty actually got bit by another Tyrannosaurus rex.

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So Scotty's bones tell us a lot about its very long

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and very violent life.

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Nothing however is written in stone.

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The chances that we've actually uncovered

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the very biggest of all time Tyrannosaurs rex

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is infinitesimally small.

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So it's very unlikely that Scotty is going

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to remain the king of the Tyrannosaurs forever.

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Tyrannosaurus rex is an animal that was around

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for millions of years.

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It can be found from across western North America.

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I find it impossible to believe that

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in all that time and space, we have been lucky enough

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to discover the single largest individual that ever was.

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There are undoubtedly bigger Tyrannosaur skeletons out there

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waiting to be found.

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And maybe smaller ones too, descendants

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of Moros Intrepidus that can continue

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to fill in gaps in our knowledge.

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We need to find more Tyrannosaurs that lived

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slightly after Moros to really understand how quickly

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they were able to grow and assume those

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top predator roles here in North America.

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In the span of a month, the world learned

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new information about two fantastic creatures

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that roamed the earth tens of millions of years ago.

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What's next on the horizon?

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How will the future shape the past?

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More species of dinosaurs are being found now

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than basically any other point in human history.

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And so we right now are in the golden age

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of dinosaur discoveries.

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There are 50 to 70 new dinosaur species named

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every single year.

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It's incredible the pace of research

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and also we're at a stage where we're able

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to apply new techniques to the study of dinosaurs

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that allow us to get new information from bones

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that we've had in museum collections for a very long time.

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We're filling in gaps in the history

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of well-known dinosaurs and we're finding specimens

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of even the most famous dinosaur that are telling us

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new things about their biology, about their growth,

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about their size, that we didn't know before.

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We are no where at the end of learning about dinosaurs

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and in generations to come, we will be knowing things

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about the lives of these ancient creatures

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that would probably blow our minds today.

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(light music)