"NARRATOR:" "The most terrifying predator of its time," "Tyrannosaurus rex." "Huge, heavily armed, relentless." "It killed and fed almost at will." "[roars]" "But not every victim went down without a fight." "[roars]" "Not every battle went T. rex's way." "[roars]" "Punishment like this should have been fatal." "[roars]" "MAN:" "We see catastrophic injuries that would kill almost any other species." "MAN:" "Some of these injuries are so severe, we can't imagine this animal being able to care for itself." "♪ ♪" "NARRATOR:" "But modern paleontology has uncovered something astonishing." "MAN:" "The terrible injuries you see in T. rex, which seem to be healing, demand an explanation." "NARRATOR:" "New fields of science and technology are starting to unlock the mystery of T. rex's incredible talent for survival." "[roars]" "The Late Cretaceous period." "The world was a very different place." "♪ ♪" "Our earliest primate ancestors hadn't yet appeared." "It was a world dominated by dinosaurs." "A world ruled by this enormous predator," "Tyrannosaurus rex." "Over 40 feet in length, 13 feet tall at the hips, and weighing more than seven tons." "[roars]" "T. rex had teeth a foot long, and a bite force of over 12,000 pounds, the most crushing of any known land predator." "♪ ♪" "They were so tough it would seem the only thing that could take down a T. rex was another T. rex." "[roars]" "Dr. Phillip Manning, Professor of Natural History at the University of Manchester in England, is obsessed by these animals' uncanny ability to survive." "PHIL MANNING:" "T. rex is the ultimate predator, known all over the world, and it's something you might not expect for such a vicious creature." "It suffered injuries through its rough-and-tumble lifestyle." "And I'm fascinated at how this mighty predator can survive these injuries." "NARRATOR:" "Phil heads up a research group that breaks the rules of conventional paleontology, using technologies developed for industry to probe the fossil record." "PHIL:" "And when we study the bones of T. rex, the use of 21st Century technology is allowing us insight into the lives of dinosaurs that we would have only dreamt of 5, 10 or 15 years ago." "NARRATOR:" "His team have analyzed dinosaurs' speed, weight and even color." "But Phil is exploring the mysteries of dinosaur survival." "Phil's traveled to the Houston Museum of Natural Science, to learn more about the serious injuries these near-invincible dinosaurs sustained, and how they were able to survive them." "PHIL:" "Oh, David, good to see you." "DAVID:" "Phil!" "Welcome to Houston!" "PHIL:" "Take me to your dinosaurs, sir." "DAVID:" "Sure!" "Let's go and have a look." "♪ ♪" "NARRATOR:" "Almost every T. rex he examines reveals evidence of a violent life." "PHIL:" "Wow!" "Every time I see a T. rex, my heart skips a beat." "Whoa!" "That's what I call a dinosaur." "NARRATOR:" "The evidence suggests that T. rex was not unlike a veteran boxer, carrying around scars from a life lived in a near constant state of battle." "But it's not the injuries that fascinate Phil, it's the fact that these animals seemed to be able to heal from traumas that really should have killed them." "PHIL:" "It seems that these animals had the remarkable ability to heal not just one or two breaks, fractures or infections, but multiple injuries at any one time." "And this is a fantastic adaptation that allowed these animals to dominate their environment." "This is something I really want to learn more about." "NARRATOR:" "To start that process," "Phil wants to find the most obvious example of a severe injury he can, which is why he's here at the Museum of Natural Science." "There's someone here he wants to meet." "PHIL:" "When you look at dinosaurs and you're trying to hunt down a pathology, an injury to the animal, sometimes it's quite tough to notice." "In this case, you can't really miss it." "NARRATOR:" "This is Wyrex." "Wyrex was discovered in Montana in 2004." "It's one of the more complete specimens of Tyrannosaurus ever found, and it has the best-preserved limbs." "Even rarer, what could be the only preserved T. rex skin." "But it's not what Wyrex has that Phil's interested in... it's what's missing." "A T. rex is supposed to have about 20 feet's worth of tail, but Wyrex's comes to an abrupt end at five feet." "PHIL:" "Ouch!" "Now, that's gonna hurt." "There's only one animal that can deliver a bite that crunched through bone like this, and that's another T. rex." "♪ ♪ [roars]" "NARRATOR:" "Phil believes that Wyrex must have been involved in a momentous battle." "Injuries on specimens show that Tyrannosaurus often fought, biting aggressively at one another's faces." "Tyrannosaur tails anchored the huge thigh muscles that gave them power and speed." "They acted as a counterbalance and a steering device, to help them make quick turns." "But the tail was also the most vulnerable part of T. rex's body." "[roars]" "It stood little chance against eight-inch, bone-crushing teeth." "[groans]" "Wyrex's foe inflicted a massive injury on him, severing more than two-thirds of its tail." "The pain and blood loss must have been tremendous." "This much, we know." "But what we don't know is whether Wyrex died from the injury, or survived." "PHIL:" "What we're looking for here is the reaction of the bone, if the animal survived, to see any evidence of healing, 'cause the bone starts knitting back together." "And remarkably, just up at the edge here where what's left of this bitten-off vertebrae here, and the rest of the tail gone, we can see a little bit of bone regrowth." "NARRATOR:" "It's incredible that a wound of this magnitude didn't kill Wyrex outright." "If he had died from this wound instantly, there would have been no signs of bone regrowth, so there's evidence he was on the path to healing, and maybe survival." "PHIL:" "So, it's just possible this animal walked away from such a catastrophic injury." "NARRATOR:" "But even if the fossil could tell us if Wyrex did heal, it still doesn't explain how it managed to get up and walk away from it all." "PHIL:" "T. rex is a beautifully balanced system." "If you're gonna remove a large portion of its balancing tail, it's got two options." "Option one-- face-plant on the ground, and it won't live very long." "Or it's got to change the way it has its center of mass over its feet." "NARRATOR:" "Phil can't tell how the loss of his tail would have impacted his balance just by looking at the bones." "He'll need a little help." "He's one of a new breed of paleontologists who take advantage of new technologies to learn more about dinosaurs and their world." "Technologies like LIDAR, which stands for Light Detection and Ranging." "It's a state-of-the-art mapping system." "PHIL:" "LIDAR is a laser scanning technology which has been used by multiple industries for mapping surfaces." "And we saw this technology and thought, 'Hang on, paleontology should be getting a slice of the action here.'" "And we've deployed it in many, many different ways, mapping our own dig sites, but also now in capturing three-dimensional representations of dinosaurs." "NARRATOR:" "Exactly what Phil needs to help him gauge the effect Wyrex's injury might have had on its ability to walk." "To map an object, the LIDAR fires infrared beams and measures distances from any surface with accuracy to within a fraction of an inch." "PHIL:" "It does this 50,000 times per second." "So with all of these points, it builds up a three-dimensional image of whatever you're scanning." "By LIDARing this skeleton, we can see whether it can actually walk." "NARRATOR:" "If you can walk, you can get away, and getting away as fast as you can is exactly what Wyrex would have needed to do if he had the strength." "NARRATOR:" "Paleontologist Phil Manning believes that T. rex possessed amazing survival abilities." "The fossil Wyrex bears signs of healing from a massive wound." "But now he wants to know how a T. rex that lost its tail ever managed to stay on its feet." "PHIL:" "To work that out, we need to build a model, a computer model." "♪ ♪" "NARRATOR:" "The beauty of having a virtual Wyrex is that it's as close as Phil can get to a portable dinosaur, that he can transport anywhere for computer analysis." "He's flown back to his home university in Manchester to upload the data to a colleague's computer." "Biomechanics expert Dr. Bill Sellers can now use his 3D modeling expertise to analyze the wounded Wyrex's movement and its ability to balance." "PHIL:" "A lot of people are arguing that it potentially could walk without the tail." "Others saying, 'No, it couldn't.'" "But there's definitely a bite mark taking off what is effectively two-thirds of the tail." "BILL SELLERS:" "My feeling is that although there's quite a lot of weight here, it's quite a heavy animal, so it's probably less than 10% of its body mass." "So it, you know, will have to do a little bit of shifting, but it would be able to do that." "I mean, you've got to imagine, it's an animal that's able to take a great, big bite out of something else." "Just think how much extra mass that's gonna add to it." "And it's not gonna fall over just 'cause it's got a mouthful of food, or it's pulling at something." "I mean, it can just cope." "Animals can." "NARRATOR:" "In other words, they might have been painful first steps, but Wyrex had a fighting chance of getting away to a place where it could nurse its wounds." "T. rex's tail wasn't just for balance." "It had muscles in its tail that were essential to its ability to walk." "Scientists believe that tyrannosaurs share a muscle arrangement with their ancestors, crocodiles, and like crocodiles, have huge muscles that connect to the leg and run halfway along the tail." "Muscles anchored on the tail pull the legs backwards, giving them thrust." "SELLERS:" "If you were a half a meter further in to the back of this animal, you'd have taken out that muscle, and then, suddenly, it would have found walking really very difficult indeed." "[roaring]" "NARRATOR:" "Despite his close call," "Bill Sellers believes that Wyrex could've gotten away from its attacker." "Even so, what happened then?" "How could it have survived for long with such a massive injury, especially in the unforgiving 'kill or be killed' Badlands of the Cretaceous?" "[roars]" "That's what Phil needs to find out." "But as he pursues his investigation, he has to confront a problem every T. rex expert has had to deal with." "Paleontologists simply haven't unearthed as many remains of T. rexes as they have of some other dinosaurs." "But Phil may have found a solution... hidden away in the private vaults of this museum in Indianapolis." "There's a dinosaur here." "Not a T. rex, but one that is closely related enough to help him provide the answers he's looking for." "Sharp teeth, powerful jaws and a taste for meat." "PHIL:" "This is my favorite, because it's possibly the ugliest dinosaur in terms of the injuries it's acquired." "And it's these injuries that tell a fantastic story about how Tyrannosaurs really were top survivors." "NARRATOR:" "This was Gorgosaurus." "This dinosaur belonged to the same family as T. rex, and inhabited the same areas in North America, just about five million years earlier." "Scientists have found many Gorgosaurus specimens." "It, too, was an apex predator of its time." "[grunts]" "It, too, has the scars to prove it." "Phil wants to perform a little dino CSI, to see just how far its healing abilities could go." "PHIL:" "Let's start with the tail in this particular dinosaur." "Now, on one side you can see in these two vertebrae from the tail, that they look quite normal." "It's only when you flip it to the other side, you start seeing that there's this huge growth of bone running between the two separate vertebrae, literally fusing them together." "So no longer do these function as two separate bones, they've become one solid lump of bone." "This is caused by some massive trauma to the tail, a pretty nasty injury." "Doesn't stop there, though." "When we get to the lower leg bone, the fibula, the smaller of the two bones in the lower leg, they look quite normal, nice and straight." "But things get different when we look to the right leg." "The tibia looks great." "When we get to the fibula, it's miserable." "This is a very unhappy dinosaur." "This shows all the evidence of a massive trauma." "This is what we call a compound fracture." "The bone is bent out, and it would've probably broken the skin of the animal." "And there's usually massive infection as a result of such injuries." "We get across to its shoulder, and this is when things really start looking nasty." "This is your scapula and coracoid." "Now, these two bones come together to form the joint, your shoulder joint, your upper arm, and it's very hard to see the joint where the upper arm bone would go in, because there's a huge growth here." "It should be nice, rod-like bone going into this plate." "It isn't." "This gnarly lump has grown." "This would've been miserably painful for the animal, but it survived." "NARRATOR:" "This lump looks a mess, but this is part of the natural healing process." "A bone callous formed to hold the broken elements together, and then specialized cells broke down and reshaped the bone." "[roars]" "It's bad enough that tyrannosaurids like T. rex and Gorgosaurus had to defend themselves from attacks by their own species." "[roars]" "But they had another problem, as well." "Some of their prey didn't give up their lives without a fight." "Horned dinosaurs could inflict deep wounds on their attackers, and all prey can bite, kick or ram." "The need to feed themselves resulted in many battle scars." "Ribs shattered across the chest and belly, fragments of bone smashed from the thigh, and an infected jaw." "PHIL:" "The pathologies that we see on the front of the jaw, the ones in the limbs, the forelimbs, the tail, how can an animal survive one or two of these, but all of these?" "Any animal on the planet today would have a real struggle for survival." "This animal flourished." "NARRATOR:" "So far, however, this Tyrannosaur fossil has raised more questions than she's answered." "We know that this family of predatory dinosaurs was hardwired to survive at any cost." "But Phil still doesn't know how." "NARRATOR:" "Dr. Phil Manning has started to put together a case that T. rex's success as an apex predator wasn't just about its size, weaponry or ferocity." "It was also, despite being injured more than once over its lifetime, very hard to kill." "But why?" "Bones can only tell him so much, but there may just be another way to pierce the veils of time." "PHIL:" "When you study dinosaurs, it can be very frustrating, because, of course, there's no living dinosaur." "You've got to look for some kind of modern comparison to help understand what's going on." "Dinosaurs are bracketed either side on their descendants, the birds, and their ancestral stock, which is including alligators and crocodiles." "So, if we can study the healing processes in the bones of crocodiles, alligators, and those of birds, we can have a fairly good idea of what we can constrain in terms of the healing processes that we're seeing in dinosaur bones." "NARRATOR:" "Crocodilians look like they belong deep in the prehistoric past." "But the similarities are more than skin deep." "Dr. Bob Bakker is Curator of Paleontology at the Houston Museum of Natural Science." "He's worked to change the world's opinion on dinosaurs, challenging established theories, and bringing the complex creatures to life, with often radical ideas." "BOB BAKKER:" "T. rex is a complicated animal, complicated in the hearing and seeing, complicated in that, like any apex predator, lunch fights back." "It could be kicked in the snout, it could be gored in the gut by a triceratops." "The terrible injuries you see in T. rex, which seem to be healing in most specimens, demand an explanation." "Part of the explanation can come from a simple experiment." "You need some bull alligators and a chainsaw." "Cut the tail off and cut off one of the legs." "A lot of those terrible wounds will heal naturally." "The immune system of crocodilians, like alligators, is tremendously potent." "Even in the bacteria-filled swamps, it heals." "NARRATOR:" "Crocodilians have an almost foolproof immune system." "The secret of their success lies in their body's first line of defense, their white blood cells." "The human immune system works the same way, and is activated by the presence of foreign bodies, like bacteria." "The white blood cells quickly isolate and seal off a wound before infection can spread through the body." "Then, they destroy the bacteria." "But crocodilians' immune system is supercharged." "They swim in bacteria-infested waters, and are frequently wounded in battles over territory or mating rights, but they never seem to get infections." "A recent study showed that their blood was able to fight off 23 strains of bacteria, including one that is highly drug-resistant." "Human blood managed to destroy only eight." "PHIL:" "If we get a scratch in that swamp, we're doomed, because of the bacterial infection." "But they have an immune system which is perfectly adapted, in phase with that environment in which they're living." "And it allows them to not only survive, but thrive with such trauma." "NARRATOR:" "And it's not just the ability to neutralize infection that makes the reptiles such tough survivors." "It's the way they're able to quickly seal off wounds." "It turns out that a scientist is studying exactly that subject here in Florida." "He's already made some tantalizing discoveries." "Phil wants to learn more." "PHIL:" "You better close that door behind you." "Oh, wow!" "What an amazing animal!" "NARRATOR:" "Paleontologist Robert DePalma has been monitoring wounds on Komodo dragons to help him understand the healing process in dinosaurs." "PHIL:" "So, where are the pathologies on this animal?" "ROBERT DePALMA:" "Right there on the right side of the creature, you see those long gashes that are filled with smaller scales?" "She got a laceration there from a bite mark." "The tooth ripped right through the skin." "Within a couple of days, that wound would've stabilized." "In a period of weeks and months, you would have had what we call granulation tissue fill in the interior." "NARRATOR:" "Granulation tissue is new connective tissue that quickly develops to provide structure while new skin grows on the wound." "It's what gives a scar its raised and tightened appearance." "PHIL:" "How similar is that healing to what we're seeing in skin impressions in dinosaurs?" "DePALMA:" "Almost identical in size and shape." "NARRATOR:" "A direct comparison can be drawn to this wound, captured in an incredibly rare fossilized imprint of dinosaur skin, around 66 million years old." "DePALMA:" "What you see is this mottled texture on the inside of the wound." "That's what happens as the granulation tissue fills that scarring." "We also see the later stages in wound healing, the contraction of the wound." "That skin is almost identical to what we see in this lizard." "Almost identical." "This Komodo dragon has a wound the same size and shape, exhibiting the same healing pattern." "NARRATOR:" "DePalma's research suggests that dinosaurs may have fought infections and healed in much the same way as modern reptiles do." "PHIL:" "I can see." "It's amazing." "You see how it's all knitted together and healed." "DePALMA:" "Absolutely." "NARRATOR:" "A supercharged immune system and a highly efficient mechanism for closing wounds." "[roars]" "These are capabilities that both prehistoric T. rex and its Komodo dragon relatives could share." "Unfortunately for Phil, this doesn't completely explain what he's seeing in the fossil record." "T. rex artifacts show a consistent pattern of self-repair and healing that rival even reptiles." "But there's another factor he's not seeing yet-- one he's about to discover." "[roars]" "NARRATOR:" "Dr. Phil Manning has found one possible explanation for how the Tyrannosaurus was able to heal from frequent and massive flesh wounds." "[groans]" "He believes they may have had the same supercharged immune systems as their crocodilian cousins, allowing them to fight off deadly infections." "PHIL:" "That's amazing!" "NARRATOR:" "But there's another piece to the puzzle of dino survival." "[roars]" "Tyrannosaurs had a remarkable ability to repair numerous traumatic fractures, something their cold-blooded relatives, with their slow metabolisms, can't do." "So, what gave the T. rex this unique healing power?" "The only way to know for certain is through the science of bone histology, the study of the microscopic anatomy of bone cells." "HOLLY WOODWARD BALLARD:" "Bone histology can reveal a lot of information that looking at the bone itself you can't get." "So this includes things like how fast the animal was growing, how old it was when it died, and even was it warm-blooded or cold-blooded." "NARRATOR:" "Dr. Woodward Ballard has ground a slice of T. rex bone so thin that it's translucent." "This will allow her to see microscopic structures within the bone, structures that should tell her exactly how T. rex was able to heal its broken bones, and if it had a fast or slow metabolism." "WOODWARD BALLARD:" "Taking a look at bone fracture histology, you see a lot of disorganized tissue around the break, if it's healed during the dinosaur's life." "And this rapid deposition of tissue suggests to us that this is a bone callus." "And since these bone calluses are found in animals today with elevated metabolisms, we can infer that dinosaurs had an elevated metabolic rate." "NARRATOR:" "Metabolism is the rate at which chemical reactions happen in the body, including growth and healing." "Birds, the descendants of dinosaurs, have fast metabolisms, grow quickly and are warm-blooded." "Their bones also heal more rapidly than alligators, with whom they share common ancestors." "WOODWARD BALLARD:" "What we can tell from looking at the mottled appearance of the bone here is that this animal was growing rather quickly." "NARRATOR:" "Dr. Woodward Ballard's T. rex bone analysis points towards one extraordinary conclusion." "WOODWARD BALLARD:" "This animal is growing more like what we see in birds and mammals, and less like we would see in something like an alligator." "NARRATOR:" "This recent revelation has changed our entire understanding on how T. rex was able to heal so efficiently." "PHIL:" "Maybe this was the perfect storm in terms of healing ability, having both the repetitive healing that we see in birds, but this amazing immune system that we see in alligators." "[growls] [roars]" "NARRATOR:" "It's a potent combination that no living animal on Earth possesses... [roars] ...and another key to T. rex's resilience." "But it also poses another mystery." "If the T. rex, like birds today, had a fast metabolism, it must have had to hunt for food frequently in order to survive." "Phil's earlier 3D LIDAR scan of Wyrex showed him that despite losing more than half of its tail, the wounded dinosaur would've still been able to walk." "But could a T. rex, with such a traumatic injury, still chase down prey and fight to the death?" "To find out, he sent the data to movement expert Scott Persons." "SCOTT PERSONS:" "The tail of a Tyrannosaurus rex is responsible for providing all the locomotive oomph." "Great, big muscle in the tail that powers the legs." "♪ ♪" "Dinosaur tails are important for balance." "You can throw your tail from side to side, to act as a counterbalance, to help you pivot and make tight turns." "[roaring]" "NARRATOR:" "Scott digitally adds the missing section of tail muscle and vertebrae to a model of Wyrex, so he can determine exactly how much difference it would have made to the injured animal's hunting prowess." "SCOTT:" "So, this is a model constructed using the LIDAR data for Wyrex." "The portion of the tail that's missing on Wyrex is really tied to its maneuverability." "In fact, the muscle's been clipped." "Having lost that big turning tail organ, it's going to hurt every time the animal takes a step." "It's lost its ability to use its tail for maneuvering." "So, the injury that Wyrex has suffered to its tail is potentially a really, really debilitating thing." "NARRATOR:" "So, Wyrex couldn't have run fast or turned quickly, which should mean starvation for an animal that relies on speed and agility to catch its dinner." "Yet we know this T. rex survived." "But exactly how is something our scientists need to find out." "NARRATOR:" "Paleontologist Phil Manning is on a mission to uncover how Tyrannosaurs were able to survive devastating injuries." "[roars]" "Injuries that should have killed them." "He's on his way to the Black Hills Institute in South Dakota, to meet a man who knows more than a thing or two about T. rex." "PHIL:" "Peter's a remarkable individual who's dug probably more T. rex than any other man on the planet." "And the insight that he brings to studying Tyrannosaurus rex is quite remarkable." "NARRATOR:" "Like Phil, Pete Larson's a paleontologist who believes T. rex had rapid healing abilities, which meant they may not have been cold-blooded creatures after all." "PETER LARSON:" "Tyrannosaurs are very, very closely related to living birds." "They have a one-way respiratory system." "Their blood system was, like living birds, had a much more efficient way of delivering oxygen to the body." "These guys had a very high metabolism." "In fact, they probably had a very high body temperature that they were able to maintain." "NARRATOR:" "The Black Hills Institute houses one of the largest collections of T. rex specimens in the world." "PHIL:" "I've never seen so many rex skulls in a single place." "How many have you got here?" "PETE:" "Well, we have nine." "Nine of the about a dozen decent skulls." "We've got nine casts here." "PHIL:" "That's just being greedy." "[laughs]" "NARRATOR:" "Not surprisingly, these specimens include many bruised and battered ones." "And like Phil Manning, Pete has been wondering how these creatures would have been able to hunt for food with such serious injuries." "PETE:" "Some of the injuries we see, for instance, a broken leg on a Tyrannosaurus rex, that would be pretty incapacitating." "So how has this animal, who needs to eat, has a fast metabolism, how is it going to survive?" "NARRATOR:" "This leads to a radical theory that just might answer that question." "PETE:" "If you have something that's gonna not allow you to chase another dinosaur, a broken leg, for instance, that means perhaps someone is bringing you food, either their mate, or family members, or members of their tribe." "NARRATOR:" "The idea that T. rex actually worked in groups is hotly debated and not widely accepted." "So is there any evidence to support this theory?" "♪ ♪" "Dr. Phil Currie believes he's found some." "He's been studying a predecessor of T. rex, another Tyrannosaur named Albertosaurus." "PHILIP CURRIE:" "This particular site, near Drumheller, Alberta, has the remains of more than a dozen skeletons of Albertosaurus." "We found evidence for small animals that are about two years old, right through to big animals that are about 24 years old." "The fact that these animals were found in exactly the same place is a good indication that at the time they died, they died together." "And the fact that they died together is also a very good indication that they were probably living together, up to the time that they died." "NARRATOR:" "This is an extraordinary revelation." "The common view of the T. rex paints a picture of a fearsome, solitary creature, dominating a primitive landscape." "[roars]" "But Currie's research suggests that Albertosaurus, a close relative of the T. rex, lived in groups." "Just like their descendants, the birds, they may have been social animals." "And if they lived in groups, it's quite possible that they hunted in groups, too." "CURRIE:" "The idea that Tyrannosaurs might be packing animals isn't so preposterous, because when we look at the animals they were eating, those animals were moving in herds through Alberta at the time." "The only way a good tyrannosaur is going to be able to eat is by gathering together into packs, and chase out something for them to eat." "I could imagine, for example, that these young, fast, agile animals, they would try and take something out of that herd." "And if they could kill it, they would do it." "But if they couldn't, they would try and chase it out of the herd, back towards the jaws of the giant adults." "NARRATOR:" "If Currie is right, and T. rex hunted in packs, it would be a crucial factor in its incredible gift for survival." "CURRIE:" "Predatory animals have a great amount of difficulty, of course, if they injure themselves, because then they can't feed themselves." "However, when we're talking about social groups of tyrannosaurs, it's a very different situation." "They're killing for the pack, and this would include an animal that had been injured, that was incapable of feeding itself under normal circumstances, and it would give it a chance to heal before it had to hunt again by itself." "NARRATOR:" "Having a powerful immune system, turbocharged by a high metabolism, could give the Tyrannosaurus almost superhero resilience." "If they joined forces and hunted in packs, these massive creatures would be an almost indestructible force." "And if the pack also hunted for an animal, injured in the line of duty, and kept it safe from attack, it's no wonder that T. rex was king." "[roars]" "But there is another survival strategy still to consider." "One that seems to work for other species, even humans." "One based on a much closer bond." "NARRATOR:" "Dr. Phil Manning is almost at the end of his quest for the secret of T. rex's extraordinary survival skills, under the most brutal conditions imaginable." "[roaring]" "What he's theorized from the dinosaur's battle-scarred bones and the fossilized tissue samples is both intriguing and controversial." "Not only did the T. rex have the ability to heal from catastrophic injuries, these giants of the Cretaceous period may have been pack hunters, cooperating in a kill that could feed the group." "[roars]" "It's a theory that undermines the image of the T. rex as the solitary predator." "This cooperative social structure could've meant the difference between life and death for a wounded animal, unable to hunt for itself." "♪ ♪" "It's also a trait we see in the dinosaurs' modern day relatives." "CURRIE:" "When you look at modern animals, we can see cooperative hunting that exists in everything from fish to mammals." "So, for example, if you look at Komodo dragons," "Komodo dragons usually aren't considered to be social animals, nor are crocodiles, and yet those animals do cooperate when it comes to feeding on large prey sometimes." "NARRATOR:" "Birds, too-- whether it's pelicans driving a fish shoal, or bald eagles preying on other birds." "It's this kind of cooperative behavior that has some paleontologists embracing a startling new theory about this ancient predator's social life that goes beyond pack hunting." "If the theory is correct, it could be the final piece of the puzzle Phil's been trying to solve." "And it has everything to do with a trait T. rex may have shared with modern day birds." "BAKKER:" "If you imagine T. rex as a 10,000-pound ground eagle, they would be strongly bonded as eagles and hawks are today, but that bond between male and female, probably was very, very long lived, maybe for the lifetime of the critters." "NARRATOR:" "Almost all species of birds form pair bonds." "Working together, they can protect their territory and share the tough job of raising their young." "[chirping]" "It may be that dinosaurs, like T. rex, formed these same kinds of relationships." "Part of that relationship could have involved caring for each other's health, through grooming, and when called for, cleaning a mate's wounds." "BAKKER:" "One member of a mated pair, licking and licking and licking and licking all the wounds, because the saliva of carnivores, even dogs today, has some potent antibacterial action." "I think both things were happening in T. rex." "Powerful immune system, something new evolved in meat-eaters, something gator-like." "And the strong bond, male and female, all grooming, licking each other every day, especially when there's a wound, a new wound, that attracts the other member of the bonded pair." "[roars]" "NARRATOR:" "Tyrannosaurus rex ruled 66 to 68 million years ago, before many mammals had evolved, and long before truly modern humans appeared, just 150,000 years ago." "[roars]" "And then suddenly this mighty predator was gone." "The extinction event that wiped out the dinosaurs also destroyed three-quarters of all life on the planet." "But buried in the earth is a stunning record of dominance and survival against all odds." "It's a story we're only beginning to understand, of complex prehistoric creatures, whose resilience may contain surprising lessons for our own human survival." "PHIL:" "It's quite clear we can learn a hell of a lot from studying predatory dinosaur bones, but especially tyrannosaurs." "We might just be able to learn something which will benefit our own species in the future, where we can generate medicines, which might allow us to heal at a much faster rate, because, clearly, these animals had the edge on us." "[roars]"