A Guide to Depicting Dinosaur Eyes

The eyes are, as many artists will know, one of the most important aspects of an animal to consider when depicting them. Without good, realistic eyes, the illustration or model will simply not succeed as strongly. Because of that, it is important to pay special attention to the eyes of a dinosaur when reconstructing them. That being said, there are still many potential ideas to consider when depicting the eyes of a dinosaur as these organs leave behind minimal trace in the fossil record of their true appearance. As a result, I decided to write an article compiling various speculative ideas regarding dinosaur eyes. This article is primarily about how to reconstruct dinosaur eyes in life and is not much about how dinosaurs would’ve used their eyes for vision or when they would be using them as diurnal and nocturnal animals, but that will be brought up when relevant. An animal’s organs are often very reflective of their lifestyle, so the two will require equal hand-in-hand speculation.

Some of the more obvious speculations one may have about dinosaur eyes may be about their color or the pupils but there, to start, there is some room for guesswork on the basic shape of a dinosaur’s eyeballs. It may seem obvious; eyeballs would be, well, ball-shaped, mostly spherical, as they are in most animals. This is not, however, a universal condition. Owls famously have slightly tubular or “bell-shaped” eyeballs, a shape that allows the eye to be overall larger while still being able to fit into a relatively small and lightweight skull. This shape is not exclusive to owls either but is also noted in some other birds of prey and is also known in some nocturnal strepsirrhine primates and deep-sea fish.

The weird, bell-like eyeballs of four different owl species. Is it possible nocturnal hunters like some dromeosaurs and troodontids had something similar? Image by Andrew N Iwaniuk on ResearchGate.

A replica of the skull of a barred owl (Strix varia). Note the super freaky sclerotic rings that project forward. Image by Bone Clones.

In owls, where this eye shape is most understood, the sclerotic ring, a ring of bone that surrounds the eyeball of many animals (including most if not all dinosaurs), is tight-fitting around these tubular eyes. This makes it so that the eye, as is the case in many birds, cannot move in the socket, hence why owls must turn their entire head to look at something.

Did some of the dinosaurs theorized to be nocturnal hunters, such as some dromaeosaurs and troodontids, also have tubular eyes? As animals that appear to have relied quite a lot on vision, it seems possible. This is something that would probably not be obvious from the animal’s exterior but is still a cool idea to consider. It may also have some implications on the neck mobility of these animals, a whole other can of worms that need not be unpacked here.

Something that would likely be more visibly obvious would be eyes that extend a distance beyond the skull. This is true of many living animals, including (hopefully) yourself. Close your eyes and feel your own closed eye (gently, don’t hurt yourself). You’ll notice that the eyeball protrudes slightly from the rest of your face. This isn’t terribly noticeable in humans but in some other animals, it can become quite exaggerated. Animals with these bigger, more globular eyes tend to be smaller and diurnal or crepuscular. It can be seen in both predators and prey, though I’ve personally noticed it more often in prey species. It’s particularly noticeable when viewing animals from odd angles, such as directly behind them.

Look at the eyes of this Chinese water dragon (Physignathus cocincinus) and notice how much they seem to bulge out from the side of his head. Some of the smaller prey dinosaurs like some ornithopods may not have been too dissimilar. Image by Donovan Snell.

On the opposite side, aquatic animals, such as many aquatic birds and crocodilians, typically have flatter eyeballs. This is believed to be an adaptation to fight against the refractive properties of water. When out of the water, these animals have blurrier vision and are more near-sighted, similar to how a human’s eyesight is when underwater. Some of the more aquatic dinosaurs like spinosaurs may have had rather flat eyes.

The eyes of this yellow-eyed penguin (Megadyptes antipodes) are very flat to the rest of the head and really don’t bulge out very much at all. Image by Bernard Spragg on Wikimedia Commons.

The size of the eyeball itself may seem like something obvious, but there is quite a bit of room for variation. Often, artists depict the eye of an animal as taking up the entire socket, but this is not always true, especially in animals that possess a sclerotic ring, which, as already stated, dinosaurs did. In many animals, such as birds of prey, the sclerotic ring is enormous and takes up the entire socket, but in others, the ring is quite a lot smaller. In dinosaurs with a similar condition, it seems reasonable that they would have eyes that are as big as the sclerotic ring and not the entire socket. Eyes are typically proportionally larger in younger animals and become proportionally smaller with age. Larger animals, even though they have overall larger eyes, tend to also have proportionally smaller eyes compared to smaller animals.

The small, mostly obscured eyes of a white rhinoceros (Ceratotherium simum), a large animal that relies little on eyesight, are smaller than one may predict based on their decently-sized eye sockets in the skull of the animal. Much of the eye in some animals ends up getting covered in soft tissue, making it invisible from the exterior. Left image by Donovan Snell and right image by Bernard Dupot on Wikimedia Commons.

The precise placement of the eyes on the head may also seem rather obvious for a dinosaur with a well-preserved skull, but soft tissue can still alter things around a bit, especially for animals whose eyes appear to face forwards. Animals with a forward gaze almost always have some degree of depth perception, an idea that, in many dinosaurs, has been examined rather extensively and could be talked about here for ages. More fitting to the theme of this article, however, is unusual angles in which an animal’s head is pointing in one direction while the eyes are facing another. Many animals have the ability to move their eyes independently of each other. This is most famous in chameleons but is certainly not exclusive to them, and is known in rats, seahorses, and many others, often with very few osteological correlates on the skull. Some dinosaurs, especially those with eyes positioned more to the side of their heads, may have been capable of moving their eyes independently, an idea that I feel has been rarely explored in artistic depictions.

Seahorses are simply amazing with all their strange adaptations. Even though is head is somewhat obscured due to the lighting, this lined seahorse (Hippocampus erectus) is likely looking in two different directions.

Many birds also have a slightly uncanny ability to be facing one way but looking another. The beak will be pointing upwards or forwards but the eyes facing downwards, as can be readily observed in herons and bitterns. Dinosaurs, if seen from weird angles, may have had very strange gazes indeed.

Herons seem to just be the kings of weird. At left, this great blue heron (Ardea herodias) was perched on a metal pole and facing foward but still able to look straight down at me. At right, an artistic depiction of a Tyrannosaurus in a somewhat similar pose. Left image by Donovan Snell and right image by John Conway.

Pupil shape is something that can be heavily linked to an animal’s lifestyle, as has been shown by Martin Banks’s very popular study analyzing pupil shape across terrestrial tetrapods. Vertically elongated pupils, the “slit pupils” seen in smaller cats, many snakes, foxes, and crocodiles, among others, are most common in ambush predators that are shorter and closer to the ground. Ambush predators hunt by trying to sneak as close to their prey as possible, and this pupil shape supposedly allows the hunter to more accurately judge the distance between them and their target without having to move the head, blowing their cover. Such a lifestyle seems unlikely for the larger predatory therapods but has been proposed for a few, such as Carcharodontosaurus, and is also plausible for many of the smaller predators.

Circular pupils are considered the “default” for modern animals and are found in almost all modern birds. The only exceptions to this are the highly-specialized skimmers that, like terrestrial ambush predators but unlike most birds, hunt at a low height.

The cat-like eyes of the Velociraptors in the original Jurassic Park are an iconic part of their design, and there may be some truth in it, given that Velociraptors seem to fit the criteria for this pupil shape. In the 3rd movie, for whatever reason, the eye was changed to look more bird-like with a round pupil. Images by Universal Studios.

If you look closely at the eye of this black skimmer (Rynchops niger), you might notice their weird, cat-like pupils. Such a condition is rare in modern dinosaurs. Image by Donovan Snell

The standard round pupil is not strongly correlated to any particular lifestyle, readily seen in predators and prey, nocturnal and diurnal, but is most strongly associated with taller predators that chase their prey over longer distances. It seems highly likely that dinosaurs like Tyrannosaurus which have been proposed to be specialist pursuit predators had round pupils. Round pupils are also likely in taller, browsing herbivores like sauropods. Herbivores that fed closer to the ground may have had horizontal pupils, as seen in many modern grazers like horses and goats. Having a horizontal pupil allows an animal to see a flat area for further and more clearly, helping in both spotting approaching predators as well as in looking for the best path of escape when a predator does arrive. This condition is certainly possible for many herbivorous dinosaurs such as hadrosaurs, ceratopsians, and others.

Horizontal pupils are pretty common across herbivorous mammals but are most obvious in goats, which, in many breeds, have light irises, making the pupil more visible. At right, an illustration showing the hadrosaur Ornatops with goat-like eyes. Left image by Donovan Snell and right image by Brian Engh.

While these three shapes are the most common, there are also all kinds of weird outliers that, while less likely, are still worthy of consideration. Many geckos have strange “pinhole” pupils that when under brighter light, constrict to become very thin with many distinct blobs, like a trail of ink.

The rather freaky eyeball of a common flat-tail gecko (Uroplatus fimbriatus) under bright light, showing off their unique pinhole look very well. Image by Bernard Dupont on Wikimedia Commons.

It’s believed that geckos have this as a way of seeing clearly in both bright light and dark conditions, allowing the gecko to both see well when hunting prey at night as well as being able to see predators when basking in bright sunlight during the day. A dinosaur that was active during both day and night may have had something similar. Another strange outlier is the half-slit, crescent-shaped pupil of the bottlenose dolphin, which is hypothesized to help the animal see well both above and under the water’s surface. Semi-aquatic dinosaurs which possibly placed their head underwater quite often like spinosaurs may have had something akin to this.

There’s also, of course, the squiggly pupils of cephalopods, but it’s highly unlikely any dinosaurs had something like this.

The color of the iris can be highly variable across the animal kingdom. Some animals have eyes that are so dark as to make it so that the pupil is barely visible, whereas, in others, the eye is vividly colored and contrasts sharply with the pupil. In many animals, such as some tree frogs, the bright colors of the eyes act as an aposematic defense. The animal, likely resting, will quickly open their eyes when disturbed in an effort to startle a potential predator and escape.

The bright eyes of the aptly-named red-eyed tree frog (Agalychnis callidryas) are hard to miss, which is, of course, the point of them. Some dinosaurs could have had bright eyes for defensive or display purposes. Image by Geoff Gallice on Wikimedia Commons.

In some animals with yellow or amber eyes, such as some owls, it has been proposed that the chemicals that produce such colors also benefit in reflecting light, which helps the animal see better in low-light conditions. Such a color is probably likely for nocturnal dinosaurs. Many birds are also even able to change the color of their eyes with the help of the sclerotic ring, almost always as part of their mating display.

The beautiful, bright eyes of a great horned owl (Bubo virginianus) may help the animal see better at night. Did nocturnal dinosaurs also have such yellow eyes? Image by Don Green on Wikimedia Commons.

This Brook’s house gecko (Hemidactylus brookii) is showing off their use of the tongue as the primary device for cleaning and hydrating their eyes. Image by Dr. Raju Kasambe on Wikimedia Commons.

In many birds, the eyelids are decorated with long, stiff feathers, similar to the thick eyelashes seen in some mammals such as camels and giraffes. In birds, these structures are primarily for display, but in mammals, bristly eyelashes serve to protect the eye from debris. I predict they would be most likely for dinosaurs who lived in arid environments and would need eye protection from sand or dust.

Commonplace among vertebrates, it is likely that most if not all dinosaurs possessed a nictitating membrane, a translucent “third eyelid” that sits between the other two and moves horizontally across the eye instead of vertically. Many birds will rarely ever close their eyes when they are not sleeping and instead, use the nictitating membrane as the primary method of cleaning and rehydrating the eyeball. Many animals use it for other purposes, such as acting as a pair of googles when diving underwater or to protect the eye from high UV reflection, such as in a snowy environment. All dinosaurs likely had one but the nictitating membrane is most likely the faster predators (who may have used it similar to falcons, who slide it over their eyes when diving at intense speed), aquatic and arid species, and polar dinosaurs.

A grey catbird (Dumetella carolinensis) with his nictitating membrane covering the eye, making the eye appear blueish, almost as if the animal were blind. But rest assured, this is entirely normal. Image by Donovan Snell

Anyone who’s had to drive on a backroad or two late at night will likely be familiar with the eerie eyeshine of many animals. This is produced by a layer of cells at the back of the eye called the tapetum lucidum, which bounces external light that goes into the eye back into the retina, allowing the animal to see better in darkness. The tapetum lucidum is quite common across vertebrates and it can be assumed that most dinosaurs had this structure as well. It is most obvious and brightest in nocturnal animals but many animals that are primarily diurnal also possess it. The eyeshine itself can come in varying colors. The eyeshine of crocodilians and birds tends to be red or white, but, in other animals, it can be blue, green, or yellow.

Hard to see with their very dark irises, this bottlenose dolphin (Tursiops truncatus) is showing off his weird, crescent-shaped pupils, which apparently help the animal see in varying conditions. Image by L. A. Rivamonte.

An interesting thing to note about dinosaur eyes is that, unlike mammals, the eyes of reptiles and birds lack any visible blood vessels in the retina. Therefore, it seems unlikely that one would see the red lines that you may see in your own eyes in the eyes of a dinosaur.

Beyond the eye itself are the accessories around it. It seems like a basic assumption that dinosaurs had eyelids, one above the eye and one below as well as a likely third one (more on this in a little bit), but this is not true across all tetrapods. The majority of gecko species have entirely lost their eyelids and instead use the tongue for cleansing and moistening the eyeball. The exact reason why this shift happened, as well as why some geckos have retained their eyelids, is not well understood. While unlikely, it is still a possibility that some dinosaurs entirely lacked eyelids and instead licked their eyes.

Eyeshine, as something humans don’t possess, looks quite creepy to us. At left, the red eyeshine of an American alligator (Alligator mississippiensis) and at right, an illustration of a Ceratosaurus with white eyeshine. Left image by Larry Lynch and right image by Julio Lacerda.

That’s pretty much everything I could think of to take into consideration when depicting the eyes of dinosaurs. Hopefully, this inspires all kinds of creative ideas for any artists reading- I know I certainly have some ideas about drawings I want to make after writing this article.

Sources

Walls, Gordon L. The vertebrate eye and its adaptive radiation. Bloomfield Hills, 1942.

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Howland, Howard C., Stacey Merola, and Jennifer R Basarab. The allometry and scaling of the vertebrate eye. Vision Research, 2004. https://www.sciencedirect.com/science/article/pii/S0042698904001646

Banks, Martin S., William W. Sprague, Jurgen Schmoll, and Gordon D. Love. Why do animal eyes have pupils of different shapes? Science Advances, 2015. https://www.science.org/doi/full/10.1126/sciadv.1500391?source=nl&utm_source=nl_pop&utm_medium=email&date=041722&utm_campaign=nl27394799&utm_content=PMP&utm_term=POP_Pop_Mech_Pro_Master_Newsletter_Subs_Current_PAID

Rivamonte, L. A. Bottlenose Dolphin ( Tursiops truncatus ) Double-Slit Pupil Asymmetries Enhance Vision. Aquatic Mammals, 2009. https://www.semanticscholar.org/paper/Bottlenose-Dolphin-%28-Tursiops-truncatus-%29-Pupil-Rivamonte/3cd6f739f57e31e08e4a0ac2c6347f368dfbe61d

Oliphant, Lynn W. Crystalline pteridines in the stromal pigment cells of the iris of the Great Horned Owl. Cell and Tissue Research, 1981. https://link.springer.com/article/10.1007/BF00233588

“Red-eyed Tree Frog.” National Geographic. https://www.nationalgeographic.com/animals/amphibians/facts/red-eyed-tree-frog

Hone, David. How Fast Did T. rex Run? Princeton University Press, 2022.

Witton, Mark. The Palaeoartist’s Handbook: Recreating prehistoric animals in art. The Crowood Press, 2018.

August 13, 2023