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Dinosaur Vision[edit]
Information on dinosaur vision is primarily formed of speculation due to the soft tissues and organs of dinosaurs not being preserved in fossil records. There are two main ways this type of speculation is accomplished. One way is through analyzing the size and position of the eye sockets in the skull, while the other is through hypothesis based on parallel evolution, to compare living species and their adaptations to extinct animals who would have evolved similar adaptive traits to fill a similar environmental niche.
In a 2011 study published in Science, Paleontologists Lars Schmitz and Ryosuke Motani attempt to differentiate dinosaurs with nocturnal habits from those exhibiting a preference for the daytime by examining the scleral ring, a small ring of bones that helped to support the pupil and iris. A wider opening in the center of this rings suggests a need to absorb more light, thus hinting towards an animal's nocturnal status. From this, researchers have hypothesized that herbivorous dinosaurs were largely preferential towards the daytime, while predators were far more nocturnal. Several researchers have since challenged this hypothesis, stating that many current day species, including birds, have a great degree of overlap in the size of the scleral ring of those with nocturnal behaviors and those with an exhibited daytime preference. These researchers also assert that without a soft tissue specimen to gauge axial length, the distance from the front to the back of the eye, one can only guess at the visual abilities of such fossils.[1]
The eyes of herbivorous dinosaurs were generally on the sides of their heads for a better view of surroundings or, a wide range of monocular vision (the eyes work independently to produce two separate images) and a very narrow range of binocular vision, while the eyes of carnivorous dinosaurs tended to be forward facing a relatively big for judging the distance of prey, or a better range of binocular vision and a narrow range of monocular vision. Both types of dinosaurs likely saw in color,[2] and an excellent ability to see movement. Most dinosaurs had proportionally large eyes, making it hard for them to orbit in the eye sockets, however larger dinosaurs like the Tyrannosaurus rex had proportionally small eyes.[3]
Saurischia[edit]
Saurischian is a clade referring to dinosaurs who have a downward and forward facing pubis bone, similar to those found in reptiles and lizards, hence the name Saurischian, which translates to "lizard-hipped" or "reptile-hipped".[4] Other distinguishing features of the Saurischian group are grasping hands that are extremely long, asymmetrical fingers, and long movable necks.[5] This included the group of Sauropodomorpha and Theropoda.
Sauropodomorpha[edit]
Sauropodomorpha is a classification of dinosaurs within the Saurischia clade. These dinosaurs all have long necks, long tails, tiny skulls, and leaf-shaped teeth. They are also all herbivores and some were bipedal, though most were quadrapeds.[6] Their actual range of vision was thought to be dependent on the movement of their necks while they eye remained mostly stationary in the skull. This meant that while having a wide range of vision to their flanks, they had large blind spots to the front and back of their head.
Diplodocus[edit]
Diplodocus' have only been found in partial remains, and no skull has been confidently identified. Instead, assumptions are made based on similar dinosaurs and through the bones of the neck vertebrae that have been identified. The eyes were presumably located on the sides of its' head, which provided excellent side vision. This would greatly help in keeping watch for predators. [7]
Argentinosaurus[edit]
Very little of the Argentinosaurus has been recovered and assembled into a skeleton. One of the things, unfortunately, missing from the fossil records we have is a skull. It is believed to have had eyes on the side of its' head, like most others in the Sauropod family.[7]
Massospondylus[edit]
Knowledge of Massospondylus is limited and constantly shifting with the addition of new information. Originally thought to be quadruped herbivores, they are now classified as bipedal and might have actually been omnivores. Proportionally they had small heads for the size of their bodies.
Brontosaurus[edit]
Brontosaurus fossils show the eyes were positioned on the sides of the head like other herbivores. It's presumed that it used it's long neck to scan the area in all directions for food and signs of danger.
Theropoda[edit]
Theropoda is a classification of dinosaurs within the Saurischia group. None of these dinosaurs were herbivores (most carnivores), but some were omnivores. Theropods could be categorized as birds. [8] Theropod Dinosaurs are known for their hollow bones, claws, sharp teeth, "three main fingers on the manus (hand); the fourth and fifth digits are reduced; and three main (weight-bearing) toes on the pes (foot); the first and fifth digits are reduced; and three main (weight-bearing) toes on the pes (foot); the first and fifth digits are reduced."[9] "Theropods generally had forward-facing eyes. This resulted in a relatively wide range of binocular vision (the eyes work together to produce one image) and a narrow range of monocular vision. They may also have had stereoscopic vision which means their eyes judged exact distances to objects or prey with evolved depth perception." [2]
Carnosauria[edit]
Most carnosaurs, including Carcharodontosaurus[10] and Allosaurus, did not have very good binocular vision, comparable to modern alligators. [3] They possessed binocular vision which was restricted to a region only 20° wide, which is understandable, as they hunted mostly large and slow prey. Their keenest sense was likely smell rather than their vision.
Deinonychosauria[edit]
Deinonychosaurs, like Stenonychosaurus and Velociraptor, had better binocular vision than carnosaurs. Their binocular field was up to 60°.[3]
Tyrannosauridae[edit]
Among coelurosaurs, tyrannosauroidea had the best eyesight.[3] The position of their eyes suggests that they had a very well developed sense of vision.
The eye position of Tyrannosaurus rex was similar to that of modern humans, but their eyes and optic lobe were much larger than that of modern humans, in fact, about as thick as an adult male's thumb.[3] T. rex, unlike most dinosaurs, had a combination of powerful eyesight and a great sense of smell. Not only is the eye position of the Tyrannosaurus Rex similar to humans, but wolves as well. This makes it easier to hunt and chase down prey because of their broad field of view. [11]
Ceratosauria[edit]
Ceratosaurs had tall, robust skulls with eyes placed closer to the side. This widened their field of vision, but decreased their depth perception.[citation needed]
Ornithischia[edit]
Ornithischia is a clade of dinosaurs with hips very similar to birds. The pubic bone on these types of dinosaurs pointed down and towards the tail like that of a bird, but they are not related to birds in any way. They also had a predentary bone at the tip of their lower jaw. The teeth of these types of dinosaurs tended to be leaf-shaped. "Most species had a toothless horny beak useful for nipping off vegetation, along with powerful cheek teeth for grinding plant matter."[12]
Cerapoda[edit]
Cerapoda is a classification of dinosaurs within the Ornithischia clade which includes two groups, Pachycephalosauria ('thick-headed lizard') and Ceratopsia ('horned faces').
Pachycephalosauria[edit]
Pachycephalosaurs, like most of the plant-eaters, had eyes on the sides of the head, so they could quickly spot approaching predators. They also had depth perception.[citation needed] Rather than finding one complete skull fossil, most specimens are found in fragments that are put together with other fragments to give us one completed picture of what the dinosaur might've been like.
Ceratopsia[edit]
Ceratopsia evolved large faceplates to use as defense and intimidation against predators. Unfortunately, these faceplates also formed massive blind spots behind the head, meaning that the dinosaur had to rotate its head and body to properly analyze its surrounding. They heavily relied on other senses along with sight to keep watch for predators, rather than relying on sight alone.
Thyreophora[edit]
Thyreophora is a group of dinosaurs within the Ornithischia clade. Thyreophora were plant-eating, armored dinosaurs. [13]
Leaellynasaura[edit]
Leaellynasaura is within a classification of its own within the Ornithischia clade, despite having only one verified species under its name. Leaellynasaura seemed to have had proportionally large optic lobes for a dinosaur of their size. The prevailing theory for this had attributed this to the fact that the dinosaur was found to have lived in the South Polar regions, meaning that it would experience long periods of time in continuous daylight and continuous night conditions. This would support the hypothesis of Leaellynasaura having adapted to live in low-light conditions. In recent years this hypothesis has been challenged, as the skull found was that of a juvenile, meaning the proportions of the skull might not have been accurate to that of an adult specimen.
References[edit]
- ^ Switek, Brian. “The Debate Over Dinosaur Sight.” Smithsonian.com, Smithsonian Institution, 3 Feb. 2012, www.smithsonianmag.com/science-nature/the-debate-over-dinosaur-sight-87825110/.
- ^ a b “Australian Museum.” Homo Sapiens – Modern Humans - Australian Museum, Australian Museum, 2 Sept. 2009, australianmuseum.net.au/image/leaellynasaura-skull-cast.
- ^ a b c d e Stevens, Kent A. (12 June 2006). "Binocular vision in theropod dinosaurs" (PDF). Journal of Vertebrate Paleontology. 26 (2): 321–330. doi:10.1671/0272-4634(2006)26[321:BVITD]2.0.CO;2. Retrieved 2017-09-12.
- ^ Britannica, The Editors of Encyclopaedia. “Saurischian.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 17 Oct. 2018, www.britannica.com/animal/saurischian.
- ^ Smith, Dave. “The Saurischian Dinosaurs.” UCMP Berkeley, UCMP Berkeley, 2005, www.ucmp.berkeley.edu/diapsids/saurischia/saurischia.html.
- ^ “Sauropodomorpha: Size Matters!” University of Maryland Department of Geology, University of Maryland, 12 Oct. 2018, www.geol.umd.edu/~tholtz/G104/lectures/104saurop.html.
- ^ a b "Walking with Dinosaurs." BBC Earth. https://www.bbcearth.com/walking-with-dinosaurs Retrieved 2018-11-15.
- ^ Ostrom, John H., and Kevin Padian. “Dinosaur.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 23 Oct. 2018, www.britannica.com/animal/dinosaur/Classification.
- ^ S, Dave. “Theropod Dinosaurs.” Introduction to the Aquifoliaceae, www.ucmp.berkeley.edu/diapsids/saurischia/theropoda.html.
- ^ Larsson, HCE (2001). "Endocranial anatomy of Carcharodontosaurus saharicus (Theropoda: Allosauroidea) and its implications for theropod brain evolution". In Tanke, DH; Carpenter, K (eds.). Mesozoic vertebrate life. Bloomington, Indiana: Indiana University Press. pp. 19–33. ISBN 0-253-33907-3.
- ^ Stevens, Kent, director. The Truth About Killer Dinosaurs. BBC, BBC, 3 Dec. 2010, www.bbc.co.uk/programmes/p00cjh26.
- ^ Britannica, The Editors of Encyclopaedia. “Ornithischian.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 17 Oct. 2018, www.britannica.com/animal/ornithischian.
- ^ Smith, Dave. “Introduction to Thyreophora.” Introduction to the Aquifoliaceae, UCMP Berkeley, 19 July 2005, www.ucmp.berkeley.edu/diapsids/ornithischia/thyreophora.html.