Tyrannosaurus rex Mystery Solved: How Dinosaurs Delivered Bone-Crushing Bites

Tyrannosaurus rex

Tyrannosaurus rex

New research addresses longstanding mystery on the anatomy of the Tyrannosaurus rex jaw.

Tyrannosaurus rex dinosaurs chomped through bone by keeping a joint in their lower jaw steady like an alligator, rather than flexible like a snake, according to a study being presented at the American Association for Anatomy annual meeting during the Experimental Biology (EB) 2021 meeting, held virtually April 27-30.

The research sheds new light on a conundrum that has perplexed paleontologists. Dinosaurs had a joint in the middle of their lower jaws, called the intramandibular joint, which is also present in modern-day reptiles. Previous research has suggested this joint was flexible, like it is in snakes and monitor lizards, helping carnivorous dinosaurs to keep struggling prey in their jaws. However, it has been unclear whether the jaws were flexible at all, or how they could be strong enough to bite through and ingest bone, which Tyrannosaurus did regularly, according to fossil evidence.

“We discovered that these joints likely were not flexible at all, as dinosaurs like T. rex possess specialized bones that cross the joint to stiffen the lower jaw,” said John Fortner, a doctoral student in anatomy at the University of Missouri, first author of the study.

Comparison of Dinosaur Fossils and Modern Day Specimens

The researchers used CT scans of dinosaur fossils and modern-day specimens to create a 3D computer model of a dinosaur jaw and identify where muscles attach to bone. They then used the model to simulate muscle forces under different biting scenarios. Stars indicate areas where strain was assessed. Credit: Image courtesy of John Fortner, University of Missouri

Fortner and colleagues used CT scans of dinosaur fossils and modern reptiles to build a detailed 3D model of the T. rex jaw. Unlike previous models, their simulations include bone, tendons, and specialized muscles that wrap around the back of the jaw, or mandible.

“We are modeling dinosaur jaws in a way that simply has not been done before,” said Fortner. “We are the first to generate a 3D model of a dinosaur mandible which incorporates not only an intramandibular joint, but also simulates the soft tissues within and around the jaw.”

To determine whether the intramandibular joint could maintain flexibility under the forces required to crunch through bone, the team ran a series of simulations to calculate the strains that would occur at various points depending on where the jaw hinged. The results suggest bone running along the inside of the jaw, called the prearticular, acted as a strain sink to counteract bending at the intramandibular joint, keeping the lower jaw stiff.

The team plans to apply their modeling approach to other dinosaur species in order to further elucidate biting mechanics among dinosaurs — and perhaps, help researchers better understand today’s creatures, as well.

“Because dinosaur mandibles are actually built so much like living reptiles, we can use the anatomy of living reptiles to inform how we construct our mandible models,” said Fortner. “In turn, the discoveries we make about T. rex’s mandible can provide more clarity on the diversity of feeding function in today’s reptiles like crocodilians and birds.”

Reference: “(R3068) The Role of the Intramandibular Joint, Symphyseal Tissues, and Wrapping Muscles on Theropod Dinosaur Mandibular Function” by John Fortner, 26 April 2021, Experimental Biology 2021.
DOI: 10.1096/fasebj.2021.35.S1.03068

14 Comments on "Tyrannosaurus rex Mystery Solved: How Dinosaurs Delivered Bone-Crushing Bites"

  1. In FL we have a good deal of experience with gators. It is well known that holding the lower jaw in place will immobilize the gator from biting. They have plenty of muscle to bring the top of the mouth down to the lower jaw. They can’t really pull up or down the lower jaw with any degree of force. Is this the situation with the T. Rex?

  2. Dudley Dawson | April 27, 2021 at 1:49 pm | Reply

    No Bonnie. The t-rex has arms that are much too short to hold an alligator’s jaw in place.

  3. Gator is a tyrannosaur a more advance tyrannosaur these are full palate dinosaur. mesoeucrocodylia like spinosaurus baryonyx gator have fully secondary bony palate because they are death roll animal that why there skull is so strong .t.rex a primitive tyrannosaur can not do the death roll because of primitive antorbital fenestra it’s not reduce t.rex is very simular predator like mesoeucrocodylia They twist there food side to side most theropod eat up and down like birds T.rex is convergent evolution allthou it and mesoeucrocodylia are first to have full palate they only have 2 finger because they are very fast land predator that crouch to the ground like most predator that why they have a furcula T.rex walk quadrupedal for short time very short time it need to launch bipedal very fast they have advance pectoral girdle same as gator allso very fast dinosaur it’s a birds convergent flight feature because of high pressure of very fast animal the early reptile had same feature as gator but died out early in evolution in later reptile it’s very rare it’s a dinosaur feature in reptile. Dinosaur arms are very well built and robust birds are not simular like that because of advance pectoral girdle they know theropod was a quadrupedal predator they learn that from last living dinosaur the gator the last living spinosauridae .gator allso is a bipedal theropod there is a scientific report from the 80,s about that .there bipedal is different from primitive theropod it’s like human they have a human ankle very rare feature in animal world because most animal walk on there toes.gator is bipedal so stop kangaroo science dinosaur is not a bird only share feature with modern crocodilian and gator is in same group as tyrannosaur they are the crown group of dinosaur .tyrannosaur usual have a lot of gator feature mostly predator feature and spinosauridae has 3 finger gator has 5 finger did not grow 2 claws it’s common in marine reptile to grow finger back .clearly gator split from tyrannosaur early with spinosauridae only tetanuran with a kink snout a common feature in modern crocodilian and gator skull is fully akinetic gator have bigger more dangerous palate full palate is very rare in reptile only found in tyrannosaur and other tyrannosaur like spinosauridae fully palate is common feature in mammal .this show dinosaur was allways primitive .palate science is a old science. Because of gator great weaponry it is the king of dinosaur and it is joke if any won call gator primitive it has fully secondary bony palate . This story I am shore it’s about famous gator second jaw joint found in t.rex and humans .

  4. William L Davis | April 29, 2021 at 11:15 am | Reply

    I thought Dudley’s response was great.

  5. I second that – it shorely flows like poetry. Exquisite workmanship; the balance of science and grammar are harmoniously locked in a death roll.

  6. No dudley, t. Rex could not do death roll because it’s arms were too short to get back up or swim, and it’s head was too tall(thick) in relation too it’s length and width. Also, it’s spine was attached to the bottom of it’s skull rather than rotated behind the skull like gator. Gators abdullah adlongota was bigger as pointed out by Bobby Boucher’s mother in 1998. Gators were do mean because they got all them teeth and no toothbrush.

  7. I wasn’t expecting to laugh this much at a science article.

  8. Trex have baby human arm. No can hold turkey leg or peepee. Gator peepee drag on ground. So human ankle lift gator peepee off ground

  9. I can see how some physiological simularities may lead some to believe the T Rex descended from ancient crocodilians but from much of fossorial evidence we’ve found the alligator along with other crocodilians are in a class of their own. Having fossils that show us an entirely aquatic crocodilian like moseosaurs and other similar fully aquatic reptiles like them. We see a divergence from this totally aquatic nature to animals that evolved to a semiaquatic lifestyle,even a terrestrial one as well but not with two legs but rather still four. With only the semiaquatic crocodilians descendants known to exist today. Ironically the largest of these know crocodilians of the past being closely related to the smallest living crocodilian of today with one other similar species, being both dwarf caimans. Which are not so much caiman with true caiman being the closest relatives these two species have. Most likely because they evolved so closely with each other, inhabiting the same region. So really a class of their own, with both the cuviers and schneiders dwarf “caiman” or Paleosuchus palpabrosus and triganatus. With the palpabrosus being the smallest of the crocodilians both descendants of the giant crocodilians such as Dieneosuchus and a few other larger of the giant crocs of the past, reaching 40’+. Fun fact… These animals are still at odds for top apex predator of their regions around the world with large constricting snakes in the boa family which split off to the pythons as well. From Titanoboa to todays Green Anaconda, and dieniosuchus to the cuviers and schnieders dwarf caiman in what is now South America, to rock pythons and. Crocodiles of Africa and Asia eating each other whenever a larger animal crosses paths with a smaller one. With Australia having scrub pythons and both fresh and saltwater crocodile eating each other. And fun fact #2 also wirh many eating smaller animals amongst their own species so cannibalistic, based on behaviors of todays crocodilians and large constrictoring snakes. All true on all continents except Europe and Antarctica. With North America no longer on that list, as burmese pythons have established populations in south florida and now both american alligator and crocodile are eating and being eaten by burmese pythons who normally live in Asia eating and eaten by crocodialians like the Philippines crocodile and im sure even the chinese alligator although they are rare and endangered still i believe… whereever both exist they become rivals. With these two animals families fighting and consuming one another for the last 60 to 80 some million years… Both tying for top apex predators even today… A little off topic but goes to show how these animals have and havent changed, just not in relation to the T Rex… Thanks for reading 😄 its just an interesting and ancient rivalry among these two such unchanged animals. But in summation to the original topic Crocodilians where already in existence before and after T rex roamed the Earth, not evolving from or into them. The data just doesnt line up with the wrong region, physiological similarities, (aside from this example of jaw ligaments and muscles being in both. Which humans also have as well) and fossorial records not really showing a link in family lineage from crocodilians to T rex as well as its subspecies which where very similar in appearance only slightly to much smaller than the t rex dependant on the species all with the same kind of anatomy though, such as walking on two legs with two small arms both with two digits and all with large heavy heads, jaws, and teeth…. Thanks again for the read. Hope it was interesting to you as much as it is to me!!!

  10. Denise M. Wright | May 3, 2021 at 3:00 am | Reply

    Why is money (possibly some tax payer) wasted on this type of study. While maybe interesting on some level it doesn’t matter how something that roamed the earth eons ago chomped its food. There are myriad pressing concerns where the effort would be better spent.

  11. Denise. While i agree its not a prevalent topic for taxpayer money to go towards, and if some did its a bit rediculous. But ive read of much more pointless and wasteful ways tax dollars have been spent. From Teapot museums to the 80%+ of the US population that can support themselves and their families, but instead are given monthly welfare checks. Usually still complaining about the amount… So id much rather see tax money and grants spent towards furthering our understanding of the living world and their connection to the past, than to the 4/5 of people on welfare and social security that are capable of being productive members of society, yet simply dont as a monthly check from uncle sam is easier… Also the multiple increases to the salaries of congress members. Many of which dont show up to important votes as well as decide to shut down whenever thwy like, still while being paid a rediculous salary… The world is not just, fair, or even free anymore. So seeing a nice productive study done to further better our scientific understanding on basically anything is better then the 3 examples i listed… 😒

  12. Coelophysis | May 3, 2021 at 8:00 pm | Reply

    Crocodilian is not in a class of there own they were allways was a dinosaur .dinosaur is a thecodont animal thecodont means crocodilian teeth .scientist allways call dinosaur crocodilian in the past they thought dinosaur was so primitive they must of form a new line and then they become advance .true crocodilian is mesoeucrocodylia animal like spinosauridae and modern crocodilian they have fully secondary bony palate .t.rex secondary bony palate is short . spinosauridae and gator type early mesoeucrocodylia secondary bony palate is short but full it is not fuse to braincase a eusuchian mesoeucrocodylia feature found in modern crocodilian like the gator .tyrannosaur have sagittal crest only found in tyrannosaur like the gator the 3 finger dinosaur tetanuran sagittal crest only found in tyrannosaur . Protosuchus a 5 finger 5 claws dinosaur have quadrupedal ankle like the gator they are not close to gator early type did not have sagittal crest just like early bipedal dinosaur with fuse ankle in tetanuran only found in tyrannosaur.mesoeucrocodylia feature they lack neural arch the big sail neural spine is not fuse if it is fuse they will die in death roll roll over that why all mesoeucrocodylia lack neural arch include spinosauridae most thecodont have neural arch some protosuchus type lack neural arch but they do not have most sensoritive face in animal kingdom and dinosaur advance feature Cingulum teeth. Allso t.rex have advance dinosaur teeth only found in modern crocodilian .t.rex have true ziphodont teeth crocodile have false ziphodont teeth .t.rex ziphodont teeth is a land teeth curve like snake monitor lizard land mesoeucrocodylia like most theropod crocodile teeth is strait a semi aquatic teeth .spinosauridae skull they have fuse frontal fuse parietal a modern crocodilian death roll feature .fuse frontal of carchodontosaurus is not well developed but they have them so they are tyrannosaur they have other tyrannosaur feature .t.rex ziphodont teeth has unique predator feature only found in land gator type mesoeucrocodylia .tyrannosaur how they swallow big prey is different from spinosauridae gator because different eating style early dinosaur or smaller dinosaur have different way of swallow prey too.modern crocodilian is advance dinosaur because they have lacrimal foramen a tetanuran feature protosuchus type lack lacrimal foramen.big sail neural spine is a modern crocodilian feature a death roll feature for large death roll muscle they do not use the leg when spinning doing the death roll it is inside movement the muscle act as motor the leg actruly is at the side it is simular to snake who lack legs .some protosuchus type have fuse parietal . Spinosaurus death roll system they is no neural arch at all by German scientist .lack of fuse nasal baryonyx there is neural arch on neck and tail just like early gator type mesoeucrocodylia modern crocodilian came from baryonyx so it was expected..modern crocodilian only on the tail.fuse nasal is found in spinosaurus one dwarf caiman t.rex primitive tyrannosaur none tetanuran theropod a land feature protect the skull from prey animal with legs.none mesoeucrocodylia dinosaur gator ankle dinosaur some have secondary bony palate but it is short not full .and modern crocodilian did not stop evolveing after they came from spinosauridae they have to fight the mammal .clearly modern crocodilian are not like other reptile they can live in cave 2 species does that today they do not need the sun or warmth of the day to hunt that why they are so dangerous.

  13. Spinosauridae did not come from t.rex they came from other primitive tyrannosaur like megaraptor or compsognathus .spinosauridae is the most primitive 3 finger dinosaur scientist found they have kink snout found in none tetanuran dinosaur and none dinosaur found in the first thecodont but clearly spinosauridae is most advance dinosaur ever and modern form alive today as the gator.they are 2 type tetanuran tyrannosaur allosaurus both came from same ancestor it’s about 2 split lines clearly allosaurus had kink snout in the past there soon be a fossil like that there the allosaurus ancestor m I can not spell it it is allosaurus because it has no kink snout so it is not a tyrannosaur it is in allosaurus line.the two tetanuran line is very different the tyrannosaur line have more mesoeucrocodylia feature.mesoeucrocodylia is 200 million years old tetanuran is 200 million years old by old chart .protosuchus type is 250 million years old they have wider tetanuran skull that is not bird like 4 finger dinosaur skull is bird like protosuchus type are older .tetanuran did not come from 4 finger dinosaur they have feature that are not found in tetanuran some are found in gator type mesoeucrocodylia but not spinosauridae or allosaurus some have palate teeth tuatara type teeth remnants of 2 row teeth lizard and thecodont ancestor teeth allso found in early dinosaur eoraptor pterosaur .flightless pterosaur is allso is a dinosaurs .early pterosaur has tetanuran stiff tail clearly it is not a tetanuran with a bird like skull 4 finger dinosaur did not have stiff tail.proterochampsa has tetanuran ankle this ankle is more advance than 4 finger dinosaur this means tetanuran is about 250 million years old clearly these are close to tetanuran a prototetanuran line.some of them have simular quadrupedal ankle like the gator the different is one of ankle bone is big only find that in dinosaur.they are going to claim that this fossil is a dead end animal they soon find fossil with all tetanuran feature they did not find one so ruling tetanuran came from a 5 finger dinosaur not a 4 finger dinosaur.coelophysis was a 210 million years old 4 finger dinosaur I think it was the oldest.compsognathus ancestor femur was bigger than the tibia like t.rex which is not bird like.one gator type mesoeucrocodylia have simular femur as compsognathus allso there ancestor have simular femur like t.rex.

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