Why are all dinosaur mouths depicted the same way?
July 10, 2012 7:22 AM   Subscribe

Super-specific roaring dinosaur question: Every picture of tyrannosaurs with open mouths (1, 2, 3, 4) seems to picture them with flaps of muscle or skin covering the corners of their mouth. Why is this so universal? Are there living animals with similar mouths that this is based on?
posted by blahblahblah to Science & Nature (17 answers total) 2 users marked this as a favorite
 
Some snakes have mouths like this.
posted by tylerkaraszewski at 7:31 AM on July 10, 2012 [1 favorite]


That's their cheeks, no?
posted by Benny Andajetz at 7:32 AM on July 10, 2012


Check out this Google Image Search for "Lizard Mouths".
posted by rocketpup at 7:34 AM on July 10, 2012 [1 favorite]


Pit bulls have this although it might be less prominent. It's colloquially called "cotton" because it looks like cotton balls. It's the muscle that controls their jaws. It's hard to see it in pictures, but it's definitely there.
posted by OmieWise at 7:37 AM on July 10, 2012 [1 favorite]


Alligators too. The cheek flaps seem to be more or less obvious depending on the mouth of the animal; nothing living today has a mouth like a T-Rex.
posted by The otter lady at 7:37 AM on July 10, 2012 [1 favorite]


Probably based on the mouths of their descendents. Google Image search of "reptile mouths" gets you all sorts of reptile photos, most notably snakes and nile crocs, where they have those flaps of skin in the corners of their mouth. Also snakes, to a lesser degree.
(Fun fact: it seems frilled lizards don't have them because they have to open their jaw so wide in order to open their frill)
So, if you were to find a present-day reptile that was closest to the T-rex, I suppose croc would be the closet. I think the meat-eaters would have that additional jaw muscle. I'll hazard an uneducated guess that this is the adductor mandibulae externus superficialis, from some looks at iguana jaw musculature.
Here's an interesting book that talks about it.
posted by Sayuri. at 7:42 AM on July 10, 2012


When you look at bones, you can see attachment points for ligaments. I assume they've found such points on T-Rex jawbones and skulls, and that would mean there would have to be a connection between the two at those points.
posted by Chocolate Pickle at 7:48 AM on July 10, 2012 [1 favorite]


Actually, start at the beginning of that chapter I linked into the middle of, Chapter 15, called "Reconstruction of the Jaw Musculature of [T-rex]." (from "Tyrannosaurus rex, the Tyrant King) Go nuts! It's fascinating.
posted by Sayuri. at 7:50 AM on July 10, 2012 [1 favorite]


One thing: those aren't skin flaps; they're skin-covered ligaments and muscles. The strength of the bite is proportional to how far from the hinge points the muscles attach (it's a same-side lever).

Without those forward-based ties, the animals might not even have the strength to hold their mouths shut (try closing a door by pushing 1" off the hinges).
posted by IAmBroom at 8:43 AM on July 10, 2012


When you look at bones, you can see attachment points for ligaments. I assume they've found such points on T-Rex jawbones and skulls, and that would mean there would have to be a connection between the two at those points.

Truth. If you look at a bone, the parts that attach to the musculature look and feel different than the surfaces that are merely covered by them. It's these attachment points that determine how all of the muscles on the t-rex look, not just his cheeks. (We know his leg muscles are big and strong because the attachment sites we've found on t-rex leg and hip bones are big. The attachment bones for his forearms are relatively tiny, so we know his arm muscles were relatively small and weak.) Someone who is very good at looking at bones (e.g. a paleontologist) can look at the attachment and determine the direction of the muscle, it's corresponding attachment point on another bone, and the approximate size of the muscle.

It's not that the cheeks are based on other lizards, it's that the cheeks are based on markings on the t-rex's actual skull.
posted by phunniemee at 11:18 AM on July 10, 2012 [2 favorites]


My pet red eared slider (aquatic turtle) has those as well although you can only see them really well when he opens his mouth wide to grab a big chunk of food.
posted by nolnacs at 1:28 PM on July 10, 2012


I used the word "ligament" wrong. I thought it also referred to the connection between a bone and a muscle.
posted by Chocolate Pickle at 1:33 PM on July 10, 2012


I didn't notice this trend until the movie version of Jurassic Park came out in 1993 or so.
posted by tacodave at 3:18 PM on July 10, 2012


I didn't notice this trend until the movie version of Jurassic Park came out in 1993 or so.

It's not a trend. It's how the dinosaur is built, and the popular images reflect how much we know about the science at the time.

What may be more relevant is how many major t-rex fossil finds there were in the late 80s/early 90s (notably Sue), and how the new things we learned from those specimens changed what we thought we knew about their traits.
posted by phunniemee at 3:25 PM on July 10, 2012 [1 favorite]


Phunniemee:

Sorry, let me clarify - I think Jurassic Park was the first place I saw this 'look' in the mainstream. Ever since, it has been normal. It's likely that you are correct and it is a reflection of fossil evidence. I just remember seeing the movie and noticing the "mouth flaps" and thinking "That's different..."
posted by tacodave at 3:52 PM on July 10, 2012


Ah, Metafilter! You guys are the best.
posted by blahblahblah at 6:42 PM on July 10, 2012


The reason those jaw muscles are visible is because that creature (and many others) lack cheeks. (They tear their food and/or swallow it in large lumps.) The kind of chewing done by us, sheep, "duck billed dinosaurs" etc. does require cheeks to stop the food falling out. Without cheeks ALL animals would have those "flaps" as you originally called them, visible, since the jaw needs closing muscles, and those muscles need to be in front of the jaw hinge since muscles can only pull.
posted by Razorinthewind at 4:13 PM on July 12, 2012


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