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Evolution - The evolution of jaws HD — Transcript

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0:01for 400 million years every top predator
0:05has needed the same fearsome piece of
0:08equipment a wicked set of jaws out of
0:12life's endless struggle predators evolve
0:15defenses evolve in response and
0:17ferocious top predators evolve again
0:20it's a vicious story of kill and be
0:23killed of escape and capture the story
0:27of Jaws
0:46the most powerful set of Jaws today
0:49belongs to the crocodilia order which
0:53includes crocodiles and alligators their
0:57fearsome bite snapped shut with 3,000
1:00pounds of bite force power
1:03on the 1/8 inch point of the sharpest
1:06front tooth 24,000 pounds per square
1:09inch
1:11twice as much power as the average nail
1:14gun
1:16the crocodile can feed on animals as
1:19large as water buffalo
1:23and wildebeest
1:34for millions of years crocodiles and
1:37every creature with a powerful jaw has
1:39held a huge advantage in the struggle
1:41for survival the presence of a jaw
1:48changes the playing field altogether
1:52what it means is that you're not limited
1:54to feeding on things that already fit in
1:56your mouth such a a great asset that the
2:01vertebrates with jaws out competed
2:03everything else in the history of the
2:08vertebrates there's probably nothing
2:10quite as important as the evolution of a
2:13jaw jaws are everywhere
2:20but once there were no jaws at all how
2:24could one anatomical feature a simple
2:27muscled hinge drive so much of evolution
2:30literally shaping many animals we see
2:33today
2:35the answers begin with the first bite
2:48in 1979 these fossils were identified as
2:52evidence of the world's first known jaws
2:55attack this is the first bite mark
2:59produced by jaw absolutely it's a lot
3:02harder to identify who did the biting
3:05the victims were tiny creatures from
3:08five hundred and thirty million years
3:10ago just a few inches long called
3:13trilobites something had taken a bite
3:16out of their side or had day where were
3:22the biters the hunt was on at stake was
3:27proof of one of the main pillars of
3:29evolution the widely accepted theory
3:32that predation animal attacks on others
3:36for food is the most powerful force in
3:39evolution because it means that prey
3:42animals that don't develop defenses die
3:45out those that do live predation has
3:51driven a variety of traits from social
3:53behavior to the evolution of armor you
3:59can see the coevolution and the
4:01escalation of this predator and prey
4:04interaction by the evolution of very
4:06thick shells as predation increased but
4:12as predation was the driver of evolution
4:14in the Cambrian who or what were the
4:18Predators that attacked and fed on the
4:20trilobite
4:22a break in the case came in 1981 when
4:27scientists pieced together for fossils
4:29thought for 70 years to be four
4:32different animals and theorized that
4:35they were in fact one giant Cambrian
4:37beast the discovery of a complete fossil
4:42a year later proved the theory they
4:45called it anomalocaris the strange
4:48shrimp in the Cambrian seas it was a
4:52monster we're talking you up to two
4:57meters in length and compared to your
4:59average trilobite during the Cambrian
5:01which might just be a few centimeters
5:03they really would have dwarfed them
5:09geologist Bruce Lieberman presides over
5:11one of the biggest Cambrian fossil
5:13collections in the world at the
5:15University of Kansas one treasure from
5:19the vault is this mouth part from
5:21anomalocaris showing clearly the world's
5:24earliest known form of a jaw
5:32it's almost like one of those pineapple
5:34slices that should get in a can and sort
5:36of a circle and inside there's a smaller
5:38circle where the hole for the mountain
5:40is and around that inner circle there
5:43are these little jagged things like
5:44teeth the strange jaw couldn't close all
5:49the way but it could tighten and clamp
5:52down like a nutcracker
5:53was it the biter lauren Babcock's team
6:00at the ohio state university went
6:02looking for a match and found it we
6:09discovered that the sizes and the shapes
6:12of the bite marks matched exactly the
6:14size and the shape of the mouth parts of
6:17anarwick heritage
6:28the discovery was huge
6:32it provided solid direct evidence that
6:35the cambrian time period was a time of
6:38kill and be killed of evolve or die
6:47so it's clear sort of smoking gun of a
6:51predator-prey interaction and that's
6:53rare in the fossil record and it's very
6:57important that it's from the Cambrian
6:59explosion in response to anomalocaris
7:06jaws trilobite s-- would evolve new
7:09defenses over time possibly even
7:12including chemical weapons we see for
7:16example the rise of greater spines or
7:19thickened spines and maybe spines that
7:22held poison glands this is really the
7:28first clear and convincing evidence that
7:30predation was a driving force in
7:32evolution even from the very beginning
7:34of the Paleozoic era anomalocaris had
7:40everything going for it
7:44but after 10 million years on top the
7:48beast disappears from the fossil record
7:50for reasons no one yet understands while
7:56the horseshoe crab is a distant relative
7:58the first killer jaw would have no
8:01descendants evolution is in many
8:06instances a battleground I mean let's
8:09face it life is intense out there
8:12species have to constantly keep changing
8:15in order to prevent themselves from
8:17going extinct it becomes a matter of
8:20life and death really whether or not
8:23individuals can adapt in time to this
8:25constantly changing environment jaws
8:29would evolve again in a huge way in a
8:34completely new line of animals fish
8:41it is 430 million years ago and fish are
8:45the first animals to have a backbone the
8:48first vertebrates they are the ancestors
8:51of all vertebrates including us but they
8:55have no jaws only openings too primitive
8:58to be called mouths they feed by
9:01literally swimming into their food or by
9:04stirring up mud counting in finding
9:06suspended particles for sustenance but
9:10in one group of fish after another a
9:12change occurs primitive fish have bony
9:17arches that hold up their gills the
9:20fossil records suggest that over time
9:22natural selection favored fish whose
9:24arches were set forward until they were
9:27able to grasp the food trying to wriggle
9:29away the bottom arch swiveled the top
9:33arch provided stability it was a
9:36structural change that enabled survival
9:39and with much variation has persisted to
9:42this day in thousands of species
9:45including our own
9:49an extinct group of fish called placa
9:53derms were the first to develop jaws
9:56this predatory edge made one of them the
9:59t-rex of the seas the exact nature of
10:04the beasts jaws has been a mystery until
10:07now I'm standing next to dung Colossus
10:11Torelli it got up to 20 feet long and
10:16probably weighed a ton or more and it
10:19was highly predatory marquest knee
10:23zoologists at the Field Museum in
10:26Chicago has been working to unravel the
10:28mysteries of dung Colossus
10:30why did its jaws grow so large
10:33how did its strange toothless jaw
10:35operate Dunkel ostia sand and other
10:39placa terms don't have teeth they have a
10:42large bony lower jaw that has an enamel
10:46covering along the rim and it is quite
10:48sharp at the tip it's like a meat
10:50cleaver West neat believes that jaws
10:55grew so large in the blades so sharp to
10:58crush the hard outer shells of
11:00invertebrates that filled the oceans at
11:03this time
11:06we think that it had a scissor-like
11:09action where the two plates would meet
11:12one another and slide past one another
11:14much like a pair of scissors West neat
11:19devised an ingenious plan combining
11:22several methods to decode the bio
11:24command X of dunks byte first he used
11:28forensic reconstruction techniques to
11:30model dunks jaw and neck muscles took
11:33measurements and calculated their power
11:37this led West neat and his team to a
11:40startling discovery
11:43dunk head muscles pulling both sides of
11:46its jaw up and back essentially a
11:49perfect example of the modern
11:51engineering structure the four bar
11:53linkage used to multiply force in
11:56everything from pruning shears to steam
11:58locomotive drive trains this to muscle
12:02opening system rapidly opened the mouth
12:04hugely wide and slammed it shut just as
12:07fast
12:13intrigued West needs team built a
12:16one-third scale model of the JA to
12:18observe the bite in action we simulate
12:22the muscle properties the speed and
12:25force of contraction of these muscles
12:27using properties from modern-day shark
12:30muscle many vertebrate muscles have very
12:33similar muscle properties and so we
12:35think that's a reasonably accurate
12:37reconstruction of what was powering the
12:39Dunkel Ostia skull the final computer
12:42calculation stunned the team dunks bite
12:45took just 70 milliseconds creating an
12:48inrush of water and a bite force of
12:511,300 pounds
12:53dunks bite fell like a guillotine the
12:57most ferocious of any sea animal ever
13:02the prey wouldn't stand a chance
13:09but like anomalocaris before dunk went
13:14extinct along with the scissor blade ja
13:17its disappearance another scientific
13:20mystery extinction is a very powerful
13:25creative force in evolution
13:29extinction will almost inevitably open
13:32up new niches that can then be colonized
13:34by other species
13:39Dunc snitch his top predator would
13:41rapidly be filled by a creature that
13:44would succeed with a new kind of jaw one
13:47that still hunts to this day
13:51sharks 350 million years ago
13:59danke las dias the fish with the most
14:02powerful bite of all time disappears
14:05from the fossil record soon sharks would
14:11rise to take dunks niches top predator
14:20why did shark survive and dunk fail the
14:24earliest sharks were probably lunch meat
14:27for Dunkel ostians sharks weren't always
14:30the top predator based on the fossil
14:33record we believe that sharks have been
14:34around roughly 430 to 450 million years
14:37and they've been around longer than any
14:40other group of vertebrates on the planet
14:41today biologist Dan Huber's fascination
14:45with sharks started early when I was
14:50about eight years old a relative of mine
14:51was attacked by a shark while surfing
14:53off the east coast of Florida and it
14:55just caused this tremendous curiosity in
14:57me and I grew up hanging out by the
14:59shark tank at the New York Aquarium in
15:04the hunt for clues to the shark survival
15:06Dan Hueber set out to make the first
15:08detailed scientific measurements of the
15:11shark's bite instead of using a
15:15potentially dangerous live shark
15:17specimen Huber got his hands on the head
15:19of a dead sand tiger shark that got
15:22tangled in a fishing line his aim
15:26construct a precise virtual shark jaw
15:29inside the computer and studied the bite
15:32from the safety of a desk chair
15:36the first step to modeling the jaw is a
15:39high-resolution CT scan using these
15:43types of modeling techniques we can
15:45actually get estimates of the maximum
15:47performance or maximum bite force of
15:49animals like sharks
15:52the system produces a digital version of
15:55the shark skull in an accurate
15:58foundation for the computer model next
16:02Huber dice X his specimen carefully
16:05measuring each muscle that powers the
16:08jaw the muscle data is then overlaid
16:12onto the CT scans skeletal blueprint and
16:15together bone and muscle form a complete
16:183d virtual jaw the cyber shark is now
16:22ready for its virtual numbers only bite
16:26when the numbers are crunched they
16:29reveal a surprising fact
16:32one thing that might surprise some
16:33people is that pound for pound if we
16:35compare them to historical predators
16:38like Dunkleosteus for example it really
16:40don't bite all that hard
16:42the Sharks Huber modeled only produced
16:45bite forces of five to six hundred
16:48pounds less than half the power of dunk
16:52so sharks can't dominate with biting
16:55power why have they been so successful
16:58for biologist Cheryl will day at the
17:02University of Rhode Island the answers
17:04begin with a body built for speed think
17:09of a shark swimming really fast chasing
17:11its prey has this nice hydrodynamic
17:13torpedo shaped profile which allows them
17:16it's a very quickly maneuver in any
17:18direction
17:19sharks have no bones to restrict their
17:22flow they are built almost entirely of
17:25the kind of flexible cartilage we have
17:28in our nose and the shark's jaw
17:30placement neatly tucked low and back
17:33reduces drag
17:37willda zaft er the first microsecond
17:39analysis of how the sharkbite works
17:43she's studying a small relatively docile
17:46shark called the spiny dogfish to
17:51capture the lightning quick bite Wilda
17:53sets up a special slow-motion video
17:55camera and then the bait a slice of
18:03herring
18:08she took it
18:16all right that's shaking that's pretty
18:20good a close-up examination of the video
18:22reveals the five-step shark bite unique
18:26in all of nature we'll go replays the
18:32five-part shark bite with a live and
18:35sedated dogfish what you see when the
18:38shark is swimming is this nice smooth
18:40profile here and when he comes up to
18:44food he elevates the cranium he
18:47depresses the lower jaw and then
18:49protrudes both the upper and the lower
18:50jaw away from the cranium then when
18:55they're done feeding everything goes
18:57back underneath the cranium and there's
18:59a nice smooth profile again and all this
19:03happens in 50 to 70 milliseconds the
19:08scientists call it jaw protrusion it
19:12gives the shark a small but important
19:14advantage you can equate this to say a
19:18sprint race if the shark can thrust out
19:21its jaws just that much further to grab
19:23the prey he's the winner by far
19:28just that little bit makes a huge
19:31difference
19:33sharks were fast shark jaws could reach
19:37out and sharks evolve teeth perfectly
19:41suited to their task
19:44back in the day sharks had small tiny
19:48icepick like teeth more for grasping
19:51than anything else but as several
19:54different groups evolved teeth became
19:56bigger but more importantly it's the
19:59shape of the teeth if you have a big
20:01triangle-shaped tooth that's serrated
20:04like a steak knife it's easy to jab a
20:06steak knife into the prey razor-sharp
20:09shark's teeth also have evolved the
20:12amazing ability to regenerate throughout
20:15the fish's lifetime and in fact the
20:22teeth are so sharp that you generally
20:24have to wear some kind of heavy-duty
20:25glove in order to get close to them and
20:27you can kind of see as we open up the
20:29jaws there's teeth better up front
20:32that's the row of teeth that they
20:33actually use to capture their food but
20:35behind each of those functional teeth
20:37there's six seven even eight teeth
20:39waiting to pop into place like a
20:41conveyor belt so that as a shark
20:43captures its food and teeth can get
20:45ripped out sharper teeth are ready to
20:47pop right into place so that they can
20:49keep on hunting without missing a beat
20:52by any measure one of the most
20:55successful life forms of all time the
20:57shark has remained the top predator of
21:00the Seas for over 300 million years
21:03its jaws unmatched
21:06but successful evolution is about the
21:09right tools for the right environment a
21:11new kind of jaw would evolve when one
21:15lineage of fish took a bold step and
21:17moved onto dry land 300 million years
21:23after sharks became the top predator of
21:26the Seas t-rex was the top predator on
21:29land but the t-rex jaw was not descended
21:33from sharks at all how did it happen how
21:37did t-rex get its bite and how could one
21:42line of fish like these with backbones
21:45and skeletons but no bite to speak of
21:48survive on land
21:58the early official we're living in the
22:00shallow water competition was probably
22:03intense for food if you can gain food in
22:06new ways that's always an advantage
22:11Harvard biologist Charles Marshall and
22:14Molly Marquis study the strange
22:16transitional creatures that lived in
22:18shallow water 370 million years ago they
22:23were fish but they seemed to be on their
22:26way to becoming the world's first
22:27reptiles they had fins with fin tails on
22:31them they had gills and then their fins
22:34started to take on structures would
22:36enable them to support their bodies on
22:38the bottom so it looks like they were
22:40beginning to locomote on the bottom
22:42using their Cotto limbs Marshalls
22:48research reveals that these limbed
22:50creatures called tetrapods evolved jaws
22:53that were also more reptile than fish
23:00this computer simulation based on fossil
23:04skull measurements shows the early
23:06tetrapod jaw in action abiding not
23:10sucking which is really interesting fish
23:13for the most part suck because waters
23:17very viscous supports the food particles
23:19well they open mouths rapidly which
23:22pulls the column of water with the food
23:24in it into their mouths as possible
23:28these guys were acquiring food in a new
23:30way which required biting in the water
23:35this basic life-form combination limbs a
23:39skeleton and a strong bite set a
23:41successful pattern for many creatures to
23:44come including us human beings still
23:50have the same form of jaw 10 million
23:56years after they first emerged tetrapods
23:59having already evolved the biting jaw
24:01were well suited to make the move on
24:04land and once they made the move their
24:08success was stunning
24:12fast forward 240 million years and
24:16thousands of species have inherited this
24:18new biting jaw by the age of dinosaurs
24:22survival is a bigger faster stronger
24:25game big jawed meat-eaters on the
24:28offense small jawed herbivores on
24:31defense carnivorous dinosaurs evolved
24:35better weapons for killing more powerful
24:37jaws teeth that were more effective for
24:39slicing through flesh bigger claws and
24:41so on
24:46herbivorous dinosaurs evolved defenses
24:49against carnivorous dinosaurs gigantic
24:53sizes horns spikes or armor in many ways
24:56the age of dinosaurs can be thought of
24:58as an evolutionary arms race
25:02t-rex certainly looks like the most
25:04ferocious jaw biter of all time a
25:08typical t-rex jawbone is six feet long
25:12stuffed with up to 50 long curved teeth
25:15at any one time like sharks if those
25:18teeth broke off
25:20t-rex just grew them back but a rising
25:27scientific theory says that t-rex was
25:29really a wimp whose arms were too short
25:32legs were too slow and eyes were too
25:35weak to bring down moving animals a few
25:39paleontologists have argued that
25:40Tyrannosaurus Rex was a scavenger rather
25:42than a hunter these scientists envision
25:45Tyrannosaurus Rex not as the fierce
25:47hunter that we all grew up with but
25:48rather wandering across the landscape
25:50sniffing out dead carcasses something
25:52like a 10,000 pound vulture
26:01Gregory Eriksson is a paleo biologist
26:04and a champion of t-rex he is having
26:08none of it
26:08tryna source Rex arguably was that was
26:10the most lethal terrestrial animal ever
26:12to have existed and easily bite through
26:16a bone like this Erickson first became
26:22involved in the t-rex debate in the
26:241990s when as a graduate student he
26:28analyzed this rare find a Triceratops
26:31pelvis riddled with exactly 58 bite
26:34marks by matching casts of the indents
26:42to fossilize t-rex teeth he identified
26:45the biter as t-rex at first glance the
26:49bite mark seemed to support the
26:51scavenger theory t-rex clearly took its
26:54time with this meal nibbling the meat
26:56off the bone but Erikson saw a chance to
26:59use the bite marks to establish a
27:01minimum bite force for t-rex and
27:04approved that T Rex's teeth could do
27:06more than just scratch a bone the T that
27:10ran asaurus rex really stand out among
27:12dinosaur teeth the sample had the
27:14largest teeth of any dinosaur this is
27:16the root this is the crown so over half
27:19of this tooth was actually usable by
27:21this animal so we have six inches of
27:23tooth that they could work with
27:25and they had a very interesting profile
27:28to them reminiscent of a say a steak
27:31knife or something like that even have
27:32the serrations on the front of the back
27:35but this really isn't like a steak knife
27:37if you look down at the end of the tooth
27:39you see that it's much more rounded it's
27:43shaped more like a railroad spike or a
27:45lethal banana even Erickson had the
27:52teeth he had the bite marks
27:55now Erickson set out to recreate for the
27:58first time anywhere the actual bite of
28:01t-rex there were hurdles to overcome how
28:04big would a tooth be that made the marks
28:07which tooth was it and the trickiest
28:10question how could he build a meaningful
28:13replica of a t-rex tooth Erickson took
28:17t-rexes reptile status as a clue all
28:22reptile teeth are made of the same
28:23materials they have an outer enamel
28:25shell which is a really hard material
28:27and inside that's the bulk of the tooth
28:29is dentine which is a type of bone
28:31essentially and together those two
28:33tissues act as a rigid body our replica
28:39here had to be a stiff and as hard as
28:41actual trying to sort teeth for the
28:44purposes of our experiment we use bronze
28:46and alumina bronze as a common casting
28:48material and with the addition of
28:49aluminum it made it a harder structure
28:52so we had to size covered here we also
28:55had the material properties
28:57Erikson fixed his t-rex tooth to a
29:00hydraulic press his plan to measure
29:03precisely how much power it would take
29:06to make the half-inch divot seen in the
29:08Triceratops bone a modern cow pelvis
29:12stands in for the prey the
29:14microstructure of cow pelvic bones are
29:17identical to the bones from Triceratops
29:23through trial and error there a horse
29:25Erickson adjust the torque until he
29:28finds a precise match for the power of
29:30the real-world bite actuator off and
29:33running far away fire
29:42she's punch straight through it Paul oh
29:46man you wouldn't want to get bitten by
29:48that how much force Paul about three
29:51thousand pounds three thousand pounds
29:54averaging many trials
29:56Erikson's final result was 3,400 pounds
29:59of bite force matching today's
30:02crocodiles for the most powerful jaws
30:04ever on earth and that's just a start
30:08probably both sides of the dentition
30:10were engaged when this animal was biting
30:12too so it's probably twice that much
30:13which would put Tyrannosaurus as having
30:16bite force and said approximately twice
30:17that of a large alligator today doesn't
30:20mean the trance or was biting at full
30:22force
30:23I suspect the Tyrannosaurus could
30:25generate fight forces perhaps three four
30:28five times greater
30:30Erikson's work doesn't prove that t-rex
30:33didn't occasionally scavenge but it does
30:36show that this ferocious giant clearly
30:39had all the tools for the job of top
30:41predator
30:49in the shadow of the dinosaurs a
30:53different branch of the first creatures
30:55to crawl on land were evolving in their
30:57own way with their own particular jaws
31:00and bite when t-rex and other big
31:03dinosaurs became extinct 65 million
31:05years ago the mammals time had come and
31:09their bite would be our bite 65 million
31:16years ago the dinosaur world order
31:19collapsed most likely in the wake of a
31:22cataclysmic asteroid impact millions of
31:26species vanished from Earth in an event
31:28scientists call the Cretaceous tertiary
31:31KT extinction for tiny mammals KT is the
31:37best thing that could have happened
31:40mammals had lived alongside dinosaurs
31:43for over a hundred and sixty million
31:45years but had almost always remained
31:46small after the KT extinction it was
31:49like an ecological release for mammals
31:52suddenly they found themselves in a
31:54world with many open niches and anytime
31:56there's an open niche some organism will
31:59evolve to exploit it that's what mammals
32:01did and that's why we're standing here
32:03today
32:06the dinosaur's demise left room for a
32:09new top predator and mammals equipped
32:12with a new kind of jaw would exploit the
32:15open niche the key to their success was
32:18specialized teeth there's an important
32:21difference between the teeth of
32:23dinosaurs and the teeth of mammals
32:24dinosaur teeth are all peg like and they
32:26all look the same
32:27within a mouth they just all look like a
32:28bunch of pigs but mammal teeth look
32:31different in different parts of the
32:32mouth today the mammal jaw has evolved
32:37to involve teeth that can extract the
32:39maximum amount of nutrition from many
32:41kinds of food incisors at the front for
32:48cutting and nibbling the food premolars
32:52set behind to tear it apart molars way
32:57in the back that compact against each
32:59other to grind the food down into
33:01digestible bits and the killer teeth the
33:05canines name not for dogs but for
33:08Carnivora the meat-eaters the canines
33:11are used to grab onto prey and hold them
33:13so for obvious reasons canines are much
33:15bigger and predatory mammals than they
33:17are in other animals now the biggest
33:22canines that ever existed were on
33:24Smilodon the saber-tooth cat
33:34Smilodon the saber-tooth cat ruled the
33:38Americas from three million to 12,000
33:41years ago in the later part of its reign
33:44this top predator most likely preyed on
33:47a physically unmatched newcomer to the
33:49scene human beings for scientists
33:56Smilodon strange and enormous 8-inch
33:59canines are a fascinating mystery why
34:04did these big cats evolve such extreme
34:06jaws that's what anatomist Frank Mendel
34:12wanted to find out animals don't develop
34:15structures without presumably some use
34:17for them and so the question is what did
34:21they do with them they would make it
34:22worth evolving in this direction
34:25Mandel devised the first-ever practical
34:28experiment designed to answer the
34:30question how did Smilodon kill first he
34:37headed to Texas for a study of smiley
34:39Dawn's relatives at a big cat sanctuary
34:42these are the closest living analogues
34:45we have for smile at home lions and
34:48tigers with three and a half inch
34:50canines are no Sabretooth
34:52but Mandel believes that their kill
34:55techniques will help him get closer to
34:57solving the mystery of smiler Don's bite
35:01modern-day big cats to bring down very
35:04large prey sometimes five six times
35:06bigger than themselves and they use
35:08their claws and teeth to pull themselves
35:10up until they can get a bite on the
35:13throat and then they clamp down on the
35:15throat surprisingly the Lions bite force
35:19is relatively mild the Lions chokehold
35:22often does not even break the skin
35:25scientists assume the big cats are
35:27strangling their victims but Mendel has
35:30a different idea my concept is that they
35:34are squeezing on the arteries which
35:36causes these animals to pass out in
35:38three to five seconds applying sleeper
35:41hold in effect the cat must then hold
35:44that for three to five minutes to
35:47deprive the animal's brain of oxygen and
35:49so the animals now brain dead and it
35:51won't fight with or give the cat any
35:54grief one problem for the lion is that
36:00the scent of the five-minute kill Alert
36:02nearby scavengers - fresh food courtesy
36:06of the lion if you're there with a bunch
36:08of other predators crocodiles hyenas
36:11other cats
36:12then those animals will come if they can
36:15and take it
36:17Smilodon spite force is even less than
36:19the lion so a five minute death grip is
36:22unlikely and evidence in the fossil
36:24record suggests these big teeth could
36:27break off in a protracted battle with
36:29enormous Ice Age prey so how did
36:32Smilodon dominate life in the Americas
36:35for nearly three million years Mandel is
36:40about to find out
36:42bringing smiler Don's killer jaws to
36:45life okay I'm gonna take this
36:50articulator attractor stands in for
36:53smiler Don's beefy body nip this up on
36:56the tractor here and helps position the
36:59big cat jaw correctly the jaws were made
37:03from a cast from a real specimen
37:10as a stand-in for one of Smilodon large
37:13herbivorous prey Mendel uses the carcass
37:17of a cow already earmarked as food for
37:19the big cats at the research facility
37:24all the animals used here died of
37:26natural causes or were in critical
37:29condition and humanely euthanized first
37:33Mendel tests one prominent theory which
37:36suggests that Smilodon might have chased
37:38down and eviscerated its prey with a
37:41disemboweling wound to the abdomen so
37:45the first thing we want to do is align
37:46these teeth here's what we want to be on
37:48this animal belly right about here
37:50there's no rib here this is abdominal
37:53wall so this is clearly a vulnerable
37:54area down keep coming keep coming
38:03Smilodon could pivot its lower jaw down
38:06a very wide 110 degrees but even then
38:10the 8 inch canines would only have 3
38:12inches of clearance would the clearance
38:15be enough to kill we can get a mouthful
38:19of skin the canines don't actually make
38:21contact
38:22they don't bury themselves in the belly
38:24wall at all
38:26so this belly bite for me at least is a
38:29very unattractive hypothesis it seems a
38:32bit of a stretch if the belly bite is
38:35out what were the canines for Mandel's
38:39theory goes straight for the jugular
38:42pretty nasty wound here why did the Ice
38:49Age predator Smilodon the saber-tooth
38:52cat evolved his 8 inch canines anatomist
38:56Frank Mendel is about to test his theory
38:59that the huge daggers helped the big cat
39:03go for the throat even though their big
39:06teeth could not survive a protracted
39:09struggle we've taken the articulator off
39:12the tracker put it on the ground and
39:14we've now placed it in front of the
39:16animals neck so in this case is gate
39:19easily span the neck no problem here I
39:22think we're in a good position now to
39:23drive these teeth go ahead guys we're
39:27applying some pressure here and there
39:31goes oh and we we certainly got
39:34penetration here with the canines pretty
39:37nasty wound here big holes
39:44holes are not enough Mandel checks to
39:47see if his replica Smilodon jaw cut any
39:50vital arteries for a quick kill I'm
39:54gonna make an incision between the bites
39:56get through the skin a lot of blood here
39:59oh yeah there is a hole right behind the
40:03airway right where the carotid live so
40:06it's a very quick penetrating wound this
40:10animal would have died within seconds
40:13Mandel believes his work explains the
40:16long-standing mystery of why Smilodon
40:18evolves such huge canines
40:21unlike lions who need up to five minutes
40:24to kill their prey Smilodon eight inch
40:27stilettos allowed them to kill and eat
40:30almost instantly preventing scavengers
40:33from stealing their meal saber-toothed
40:37cats
40:38I think they drove these teeth through
40:40the animals neck and the serrations on
40:44of these teeth cut one of those carotid
40:49it would bleed out almost instantly and
40:51therefore kill it more quickly than the
40:54sleeper hold of modern-day big cats
41:00Smilodon became extinct at the end of
41:03the Ice Age 12,000 years ago perhaps due
41:08to the sudden change of the climate or
41:12perhaps because early human hunters out
41:14competed them for prey as the new top
41:19predators humans were fearsome but their
41:22jaws were puny how did humans succeed
41:26with jaws that are now so small that
41:29even our primate cousins have bigger
41:31bites humans are anatomical wimps
41:35compared to a chimpanzee we are we are
41:38weaklings Scott McGraw is an
41:43evolutionary anatomist who studies
41:45primates and the extinct relatives of
41:47humans hominids if you look at the great
41:53apes today gorillas chimpanzees
41:55orangutans and bonobos they're chewing
41:58in many cases tough fibrous vegetation
42:02or hard fruits requiring large powerful
42:05jaws and and jaw muscles and if you look
42:09at the size of their teeth you can see
42:11that the molars of these animals are
42:13larger than modern humans sometime
42:20around 1.8 million years ago our hominid
42:23ancestors who had been standing on two
42:26legs for some four million years lost
42:28most of their body hair grew their
42:31brains and walked right out of Africa to
42:34spread across the world
42:38today homosapiens us dominate all life
42:42on earth we did it with intelligence not
42:46brute strength and built tools that
42:49lessen the need for powerful jaws during
42:53human evolution there is clearly a
42:55transition from physical strength and
42:58strength and biting for example to using
43:01our brains essentially we were able to
43:03outwit our predators and so there was a
43:06transfer of weaponry from the physical
43:09individual to the tools that that
43:11individual used through two million
43:17years of tool-making our jaws have
43:19shrunk dramatically as there was no need
43:22to sustain their enormous size our jaws
43:25are commonly no longer even big enough
43:27to house the wisdom teeth that grow in
43:30young adults in the future scientists
43:33theorize wisdom teeth may disappear
43:36altogether our teeth are shrunk our jaws
43:40are shrunk our chewing muscles have
43:42shrunk that has to do with our relaxed
43:44diet we can just shove something in the
43:46microwave we don't need to have big
43:48robust teeth and jaws and muscles to
43:51process our food we don't even need
43:53teeth just a straw
44:02for half a billion years many top
44:05predators have had the strongest bite in
44:08their environment
44:16today it earns them a place in the zoo
44:19but 400 million years of evolution
44:23proves that the only constant is change
44:29the thing that's exciting about
44:31evolution is that at every generation
44:34the rules are slightly different than
44:35they were for the generation before so
44:37sometimes a strategy that you have in
44:38place now isn't necessarily going to
44:40work in the future perhaps we humans
44:44should not get too comfortable with our
44:47place on top

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