Did T. rex Have Lips?

few things in paleontology managed to incite more discussion and controversy than the life appearance of the most iconic and awesome non-avian dinosaurs the extent of feathers and tyrannosaurs the anatomy of spinosaurus and the lip debate much of the paleoarts produced in the last few decades has followed a trend wherein the ferocious non-bird theropods are almost always burying their teeth at the observer the formidable weaponry on clear display for all to see however in even more recent years there's been some interesting discussion about this and whether or not exposed teeth in beakless theropod dinosaurs such as t-rex is actually the correct way to restore them or if they should in fact have their teeth covered over by lips when their mouths are closed this did actually used to be the way a lot of older reconstructions portrayed extinct dinosaurs but gradually over time the tendency has shifted towards showing off the teeth and this has inevitably led to a lot of disagreement among paleontologists and paleo enthusiasts before we start looking at the arguments for and against lips and non-avian theropods it must be made clear that there isn't exactly a scientific consensus on this topic yet and indeed there has not even been all that much actual peer-reviewed study on it yet nevertheless there is much to be said about lips and the evidence in favor of them is very good first of all though what are the arguments against lips one of the main contentions against the presence of lips and extinct dinosaurs concerns the phylogenetic bracket phylogenetic bracketing is a method used by paleontologists when they wish to determine how likely it is that a certain character was present in an extinct organism by looking at its living relatives so in the case of extinct dinosaurs we would look to birds living dinosaurs as well as crocodilians the closest living relatives to birds the extinct non-avian dinosaurs are then bracketed between these two groups and it can be inferred that a condition present in both living groups is probably quite likely to have been present in the extinct group too so when we look at the lip conditioning birds and crocodilians what do we see well obviously birds don't have lips they have beaks and neither do crocodilians therefore the argument goes that non-avian dinosaurs must have lacked lips too but as we'll see it's a little more complicated than that another common argument against lips and dinosaurs is to do with measuring how far teeth in the upper jaws extend down and overlap the lower jaws when the mouth is shut with it being thought that the teeth of many dinosaurs were simply too big to have been covered by any sort of extra oral tissue but the main argument for liplessness is based on the anatomy of the jaw bones themselves namely their texture and small holes located along them called labial foramina these holes allow for nerves and blood vessels to pass from the skull to soft tissues around the jaws and according to some research there is a potential link between the number of foramina and the amount of tooth coverage with animals that have many foramina tending to have teeth that were exposed such as crocodilians while those with fewer foramina possessed lips or cheeks that covered their teeth it's therefore been argued that the higher count of foramina and extinct theropod such as tyrannosaurs is evidence of a crocodilian-like lack of lips the bone texture of theropod jaws particularly tyrannosaurs has also been compared to that of crocodilians perhaps most notably in a 2017 paper by paleontologist thomas carr and colleagues in which the new species displetosaurus horneri was named and described this research examined the bone texture in several areas across the skull and inferred a variety of skin coverings for them hypothesizing that the rugos texture on the maxilla was similar to the texture seen in crocodilians and as such tyrannosaurs lacked lips the foramina were also suggested to have made the snouts of these animals incredibly touch sensitive instead of being to support lips so there are the main arguments that have been made against a lipped condition but now let's take a look at the counterpoints starting with the phylogenetic bracketing argument the problem here is that non-avian theropods clearly have very different jawbone anatomy compared to living birds and crocodilians so in this case phylogenetic bracting is not as sturdy as it is at other times if you compare a crocodilian skull to that of a theropod such as a tyrannosaur you can see that while the crocodilian possesses a curved edge to their mouth with teeth placed towards the inside tyrannosaurs have teeth positioned close to the sharp edge of their mouth additionally the lower teeth of crocodilians will often be interdigitating between and even growing to be on the outside instead of the inside of the upper teeth when the mouth is shut plus a number of their teeth will sometimes stick directly out to the sides or the front which they're able to do since there are no lips to stop them however with most non-avian theropod teeth the lower rows are pretty much in line with or positioned to the interior of the upper row and in the majority of cases you don't see any of the extreme tooth protrusion to the sides that you get in crocodilians therefore the phylogenetic contention is severely weakened by the fact that the anatomy of these ancient animals is so clearly different to their living relatives if you wanted to continue along the phylogenetic line of thought though it's also important to note that lips are actually the more common condition among tetrapods apart from crocodilians and certain species of freshwater dolphins all other living tetrapods with teeth possess some form of lips whether they're just thin bits of skin or heavily muscled structures therefore since they're so common and lacking lips is apparently the rarer specialized condition it's reasonable to assume that lips were the default ancestral condition for all tetrapods increasing the likelihood that certain dinosaurs had them too the argument about the length of teeth and how they were just too large to be covered by lips is also a little misleading as one of the issues facing previous attempts to measure the extent to which the upper teeth overlap the lower jaw when the mouth is closed is the effect of tooth slippage after death in which the teeth look longer than they would have appeared in life due to them sliding slightly out of the sockets additionally in various living animals it turns out that the mouth is not actually fully closed even when it appears to be instead being held slightly open behind the lips providing more space for the teeth to fit plus there's also the fact that soft tissues can cover a surprising amount of dentition with a good example being water monitors despite their skulls clearly showing some fearsome looking and decently sized teeth many times when their mouths are opened you cannot see these teeth at all they're completely hidden by soft tissue all sorts of living animals with formidable dentitions actually quite easily obscure these structures from the outside with the use of pouches or pockets hidden by lips and it's entirely possible that large non-avian theropods did the same the texture of the jawbones and tyrannosaurs being similar to the texture of crocodilian bones was another of the arguments made in opposition of lips the 2017 paper i mentioned earlier asserted that the texture in crocodilian skulls is identical to that scene in tyrannosaurs apart from the entire skull of crocodilians has this texture while in tyrannosaurus is limited to certain regions and why would bone surface texture be significant in determining skin types well in crocodilians the skin is actually a major part of shaping the underlying skull surface and as the animals get older the bony ridges around the foramina openings are grown due to tissues from the skin becoming ossified turned to bone enhancing the distinctive texture of their skulls so it's suggested that tyrannosaur's skull texture being like a crocodilians would indicate a correlation between the overlying skin type implying that tyrannosaurs had a lipless crocodile look the paper also correlated a lot of other bone textures from across the tyrannosaur skull implying skin types such as armored skin cornified sheaths and large scales in locations around the eye and along the top of the skull however many paleontologists disagree with the contention of a crocodilian-like liplessness as the bone textures around the mouth just don't seem all that similar when looked at in detail in paleontologist mark whitton's blog post on the subject he points out how although tyrannosaurs do show some extent of sculpting of the jawbones as they age the rugosity never reaches the same extent as the highly complex patterns observed in adult crocodilians and therefore it would seem pretty clear that tyrannosaurs didn't have the same skin overlying these areas as crocodilians do since the sculpting isn't the same the crocodilian-like texturing is also absent from the lower jaws of dinosaurs such as tyrannosaurs and instead there's a large roar of foramina here that isn't present in crocodilians paleontologist scott hartmann suggests that if these structures were supporting the bottom of the lower lip then this could be representing a potential tooth pocket for the upper teeth when the mouth closed additionally the way the royal foramina gets closer to the top of the mandible the closer to the front of the jaw they are is quite noticeable and could be due to how the pre-maxillary teeth of tyrannosaurs are much smaller than the maxillary teeth further back therefore not needing as deep of a tooth pocket at the front of the mouth the number of foramina and tyrannosaur skulls was another major part of the argument against lips with it being thought that the many foramina present in tyrannosaurs put these animals in the same league as crocodilians with their incredibly high foramen account and therefore that liplessness is more likely some fascinating findings concerning foramen account and extraoral tissue coverings were revealed by the work of ashley moreheart who as part of her master's degree in 2009 investigated the link between the foramina and extra-oral tissues in many living animals finding that there is a rough statistical correlation between the characteristics when comparing non-avian dinosaurs to the living animals it was then found that they did indeed fall within the range of living animals with extra oral coverings additionally while tyrannosaurus in particular do tend to have a greater number of foramina when compared with other dinosaurs the number is not that high when compared to crocodilians crocodilian jaw bones tend to average at about 100 foramina and can get as high as over a thousand foramina per bone in some specimens whereas none of the tyrannosaurus jawbones looked at in the 2009 research reached over 81 as well as this there also appears to be a slight correlation between foramen and number and the size of the jaw so that longer jaws tend to have a greater number of foramina and therefore the higher average foramen count in large tyrannosaur skulls seems even less exceptional especially since much smaller crocodilian skulls still massively outnumber the tyrannosaurs in their foramen account and smaller tyrannosaurs have a count that's very much in the range of many other animals of their size more heart also found that among living animals those with foramina values averaging 50 or below per jawbone had soft and pliable extra oral tissues that cover the teeth while those between 50 and 100 had immobile facial tissues and only those with an average of above 100 foramina can definitely be said to lack coverings for their teeth so following these cutoff points many beakless non-avian dinosaurs fall well below the 100 mark and even the certain tyrannosaurus with elevated numbers are below 102 seeming to indicate lips or some sort of tooth coverings were indeed present in these prehistoric creatures this research is not as extensive as it could be however and there are a few complexities with the data but it is a good general guideline that hopefully will be expanded upon with future studies that can help us to more reliably predict the extent of tooth coverage in prehistoric animals another point that's worth quickly looking at is the size of the foramina themselves as mentioned in mark whitton's post the foramina located higher up on the skulls of tyrannosaurs actually tend to be much smaller in size than those found in their other mouth but in crocodilians the variation in foramina size has a much lower range inferring that while modern crocodilians have a pretty similar skin type across the whole of their jaws the tissue types were probably much more variable across the faces of tyrannosaurs something we'll come back to in a bit so to summarize personally i think the evidence in favor of lips for non-avian theropods such as tyrannosaurs is much more convincing than that against them while phylogenetic bracketing would imply crocodilian-like mouths the highly disparate anatomy seen in dinosaurs greatly outweighs this argument and by looking at comparisons with other living animals it seems much more plausible that these reptiles did indeed have some sort of soft tissue covering for their teeth however we still cannot be 100 sure it's important to remember that this is still an ongoing area of discussion and while the current evidence heavily favors the prolips side cases from living animals show that nothing is ever certain a good example cited in mark whitton's excellent book the paleo artist's handbook is the conflicting state of the clouded leopard and the tasmanian devil the clouded leopard is an excellent instance of what i mentioned earlier where creatures with huge teeth can actually completely conceal them from the outside these cats have relatively massive canines compared to the size of their skull yet you can't see them at all when the mouth is closed but then you come to the tasmanian devil looking at its skull you'd think that all of its relatively moderate-sized teeth would be concealed especially if the clouded leopards could be but then you'd be wrong as in fact the upper canines of these mammals are continuously exposed even when their mouths are shut so as with many other cases it's nearly impossible to apply a general rule to the natural world without nature being nature and providing some exceptions the next question then after establishing that non-avian theropods most likely had extra oral tissues covering their teeth is what sorts of lips did these animals possess well in tyrannosaurs at least the average foramen account being in the 50 to 100 range would seem to indicate that immobile facial tissues are most likely the sort of lip structures seen in modern lizards but as i alluded to earlier the faces of tyrannosaurs were probably very variable things with all kinds of different skin types covering different regions of the skull the 2017 paper describes how based on observations of the osteological correlates large areas of the upper skull were probably covered in armor and cornified's toughened skin as well as larger scales that have been proposed to be for ornamental display purposes in witten's blog post he explains how on many tyrannosaur skulls there are very noticeable shallow depressions that are roughly elliptical in shape and with raised ridges of bone around them positioned a bit above the labial foramina these structures are variable in the way they're patterned among the different tyrannosaurin tanks are but they are very likely formed due to the effects of overlying epidermal scales it's therefore possible that the ridges between the depressions had vertical rows of large scales on top of them in life in addition to tougher armored skin over the higher areas of the head and around the eyes which might have protected the animals during their famous face biting behavior however instead of a crocodile-like lack of lips around the mouth it seems more likely that the tyrants had an immobile lizard-like tooth covering it's a fascinating interpretation of tyrannosaur facial anatomy and one that presents a picture of an awesome and charismatic creature but again it's important to remember that we can't yet be entirely sure about all of this though the evidence is pretty good and mark whitton's brilliant paleoart is a truly convincing looking beast before we end this video i'd also like to have a quick look at one dinosaur in particular where the debate about lips is especially prevalent spinosaurus spinosaurus and potentially other spinosaurs seems like the dinosaur that would be the exception to what we've talked about so far their jaws are pretty similar in overall anatomy to those of modern crocodilians they have long teeth in their premaxillary at the tip of their snout and some of the teeth in the lower jaws are actually on the outside of their upper teeth when the mouth is closed which is unlike the condition in many other theropods we discussed earlier so was spinosaurus lipless like a crocodilian well not necessarily in mark whitton's recent post about the new reconstruction of this animal he points out how first of all the foramina count is actually not that high and is in fact well below the threshold for liplessness additionally the foramina of the maxilla and dentary are aligned along the edge of the jaws like the conditioning lizards and not spread across the whole jaw bones like in crocodilians plus they're positioned far enough away from the edge of the jaw that the base of a soft tissue lip structure wouldn't be in the way of the teeth on the lower jaw overlapping the upper teeth as well as that the bone texture is not at all like crocodilians which we've established is the result of the overlying skin reshaping it again indicating a discrepancy with crocodilian anatomy witten also puts forward the argument that the supposed link between liplessness and an aquatic lifestyle is not actually as strong as it has been made out to seem in the past while it's true the river dolphins and crocodilians are examples of fish feeding aquatic tetrapods that have exposed teeth there are many more examples of fish eating tetrapods with lips such as water monitors cetaceans certain snakes seals and others so it's definitely not out of the question that spinosaurus retains lips too now you may be wondering in the end does any of this really matter who really cares about such a small detail as lips and dinosaurs well i'd argue that it is pretty significant since the implications of this debate have a direct impact on how we restore some of the most iconic prehistoric creatures and media and as a result on the public perception of dinosaurs as a whole by shining light on the discussion surrounding the subject we can show people how paleontology is done and what the evidence is and how it's used to come to these conclusions the lip debate is a fascinating part of modern paleontological discussions and it's been a lot of fun to learn about hopefully we'll see more research into this aspect of dinosaur life appearance in the coming years and as a result we can be more confident in our reconstructions of these iconic prehistoric animals well i really hope you enjoyed this video and learned something new a big thank you to our patreon supporters especially our dinosaur tier supporters jan owen corey peterson george frogtech mike pace persian boy mayor's world dhruv srivastava matthias bergshire jacob stewart nicole bueno pasta mark thorne dominic bathey harry everett and alex hawk if you would like to find out more about her world its history and the wonderful life that surrounds us all please feel free to subscribe to the 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Channel: Ben G Thomas

Views: 506,842

Rating: 4.9448538 out of 5

Keywords: Biology, Science, Paleontology, Palaeontology, Dinosaurs, Animals, Nature, Wildlife, Ben, Thomas, Prehistory, Anatomy, Fossil, Bones, News, 7Daysofscience, Days, of

Id: ZyoxPknp670

Length: 17min 58sec (1078 seconds)

Published: Sun Jul 19 2020

Reddit Comments

[u/Lego_GeneralGreivous]

Um.... I’m pretty sure it was a joke.

The entire thread above/below this reply.

[u/RandomedOne]

I don't see any real reason for any Theropod to have lips though,
teeth may dried out without any covering but covering isn't necessary the lips especially now that we know Sauropod basically have beak growing on top of their teeth covering it there is no reason to assume Theropod don't have the same structure,
teeth cracking also get overplayed as reason lips is required for terrestrial animals elephant have two colossal tooth protrude outside of their lips and it seem to do just fine considering teeth replacement rate in dinosaurs lips covering just seem unnecessary.
funny irony being that only Archosaur with lips are Softshell-turtle which are strictly aquatic.