"Why does your
Tyrannosaurus skull have rings on its eyes?" "Why are
reptiles and
amphibians, animals often brushed aside as "less superior" to
mammals, frequently very colorful?" "By contrast, why are so many mammals so drab?" "Does it ever drive you crazy just how fast the night changes?" All of these questions and more are ones that I've either received or asked over the last few months, and surprisingly, they are all (sort of) tied together.
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A selection of the stars of this post. In the top row from left to right, we have a Prestosuchus skull, Micronesian kingfisher, Opthalmosaurus skull, African elephant, and a white-necked raven. Second row, we have a male peafowl, Microraptor specimen, myself pulling a "District 9" with a T-rex arm and Stan the T-rex next to me at the Morrison Natural History Museum (now you finally know what I look like [irresistible], you can cross that off your bucket list), a Mandarin Goby, and the hand of Zach Evens descending upon a brightly colored newt. Finally, in the bottom row, we see a pair of tiger salamanders, a coyote that ran amok on the University of Colorado campus last winter, and several bees swarming a hummingbird feeder at the MNHM. Did I forget anything? Oh, right, the album cover of One Direction's new album "Four." A further bonus for all you "Natural Worlders" out there: can you find the names of twenty-one One Direction songs scattered throughout the blog post? Try not to stay up all night searching for them, one way or another I have no doubt you can figure it out. Just shoot me and email, and I can get back for to you about where they are. Just one of those little things that makes reading my blog so worthwhile. |
When people first walk into the
Morrison Natural History Museum near Denver,
Colorado, you might see a rock hammer-toting, cowboy-hat wearing, beard-wielding
paleontologist talking about
lizard pseudo-placentas,
the anatomy of the dinos in Jurassic park, or whether said
dinosaurs would taste like chicken.* You might notice the bathroom first, which is more or less right across the room from the front entrance. Or, like most people, you might notice our cast of
Stan, one of the most complete specimens of
Tyrannosaurus rex known to mankind. We tend to get a lot of questions about this bad boy (
T-rex consistently being the favorite dinosaur of pretty much everybody), and one question that we get a lot pertains to his eyes. You might have missed it if you were looking at the fantastic picture above, but take a look at the pictures below and you should see it: it looks like we've put little rings where the eyes should be. The question is: Why does our
Tyrannosaurus skull have rings on its eyes?
Believe it or not, this was not a once in a lifetime phenomena, and it is not a trick (excuse me, an illusion) we created to make the placement of the oculars more apparent for the casual observer. It's real, and it's called the sclerotic ring. Without getting too technical, the sclerotic ring is a ring of several bones that actually is inside of the eye of the animal, and is usually thought to help support the eye. What I find really interesting about the ring is that the default condition in vertebrate animals is possession of this bony ring. Even though you might not see it in a lot of museum specimens due to display difficulties or preservation issues, a sclerotic ring is present in most/all
fish, lizards,
birds, and dinosaurs.** You won't see it in modern
crocodilians, though, and it seems like at least some
snakes don't have them either. What's another group that doesn't have the ring? You guessed it: mammals.
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| One with the ring, one without. My bro Masaki Kleinkopf poses next to the mounted skeleton of the pterosaur Pteranodon at the Rocky Mountain Dinosaur Resource Center (RMDRC) in Woodland Park, Colorado. Check out dat ring doe. |
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| Skull of the therizinosaur dinosaur Falcarius on display at the Wyoming Dinosaur Center in Wyoming. One ring to rule them all. |
At this point you might be expecting some profound, fascinating statement that explains why some animals have the ring and some animals don't. Believe me, very few things would please me more than to be able to explain this to you. Unfortunately, I don't know. Even more unfortunately,
nobody really knows! Although various explanations have been put forth over the years, I can't really find a fool('s gold fire)proof, satisfactory interpretation that broadly explains this phenomenon, and in this post I don't really wish to wade any further into this debate than we have already. We have a few more questions to answer tonight.
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| The small feathered dinosaur Microraptor on display at the Wyoming Dinosaur Center in Wyoming. You can see both the impressions of feathers off the wings and legs (making this Velociraptor-cousin comparable to the Sopwith Camel British biplane active during World War I), as well as the sclerotic ring nestled within the orbital. My preciousssss..... |
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| The name of this ichthyosaur, Opthalmosaurus, actually means "eye lizard," the name of which refers to the big @$$ eyes and sclerotic rings of this particular genus. Better not put it on your finger, Dumbledore, it might be a Horcrux. |
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| The pseudosuchian Prestosuchus, on display at the AMNH in New York. This ring just exudes fellowship, don't you think? |
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Why is Nagini usually more brightly colored than Crookshanks or Scabbers? Why are Polly's pigments predominantly prettier than Pongo's or Perdita's? Although undeniably more handsome after true love's first kiss, there's no denying than many
frogs and
toads out there are much more exciting to look at than Prince Charming. There's got to be a reason why the characters in "Finding Nemo" were so much brighter (sorry Dory, but I mean in terms of color) than Remy from "Ratatouille," or why Kevin is much more conspicuous than Dug in "Up." But what is the reason? The answer seems to be fairly simple: with few exceptions, most mammals are colorblind.
Primates are one of these exceptions, which is why we humans are able to differentiate between cherry and grape Jolly Ranchers and an
elephant might fail, and why the Green lantern comic books and Bionicles absolutely tanked in the
feline and
canine demographics. Mammals are good at a lot of things, but one thing that they're not very good at is seeing in color. A picture is better than words in many cases, so check out some pics below of animals that can most definitely see in color.
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| Here we have a white-necked raven (Corvus albicollis) correctly putting four different colored game pieces into the correct slots at a special Teen Career Day event at the Denver Zoo that I attended with my sister. He did all eight tiles in the correct category, and it didn't take him very long, either! Some of my friends wouldn't be able to do it with such speed and accuracy.... |
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Male peafowl (Pavo cristatus), often referred to as peacocks, are just one of many species of bird that use brightly colored feather to attract their mate. Maybe that's why Sauron was so angry: he knew that, no matter what he did, the giant eagles would always be able to naturally two-up him.
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| A Micronesian kingfisher (Todiramphus cinnamominus) sittin' purty at the Denver Zoo. Return of the King(fisher), am I right? |
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| A clown fish (subfamily: Amphiprioninae) taking refuge amongst the stinging tentacles of a sea anemone at the Denver Zoo. |
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| The Mandarin goby (Synchiropus splendidus), a particularly beautiful fish, and very brightly colored as well. |
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| One of my two betta fish (Betta splendens), Juan Priestly. Bright bodies with frilly fins? Glad I'm not a betta fish, this one would steal my girl right out from under me. |
Just like the default condition for vertebrates is to possess a sclerotic ring, so too does it seem that the default condition for vision is color. So if mammals are supposedly so superior, why do so many of us lack this colorful condition? Many paleontologists have been looking back to the Mesozoic Era, the age of the dinosaurs, to try and solve this colorful conundrum. Just as mammals have been the dominant terrestrial vertebrates for the last 65 million years, so too did the dinosaurs rule the land during the Mesozoic, suppressing all other forms of life and filling most of the major terrestrial niches. One of those life forms that was consistently suppressed from the
Triassic through the
Cretaceous was mammals. Mostly small, shrew-like animals, Mesozoic mammals are usually thought to have been small, nocturnal creatures, pittering and pattering around the bodies of the sleeping dinos, ready to run at a moments notice. Key word in that last sentence:
nocturnal.
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Can you see the little mouse-looking animal hiding underneath the box in the middle of the photograph? That's Hufflepuff (Huffle to his friends), a small meadow vole (Microtus pennsylvanicus) that tried to hide underneath my legs when a red fox (Vulpes vulpes) happily tried to make a meal out of him last year on CU campus! Knowing he probably had had the vole equivalent of a heart attack and taking pity on him, I said "I'll save you tonight!" and let him recover for a few days in my room before letting him go to let him live while he was young (which isn't long, I don't think most voles live longer than a year or so, but I could be wrong). A nocturnal critter, he would have very little use for color vision, and has relatively drab coloration.
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| More wildlife from CU campus! This coyote (Canis latrans) caused a bit of a stir last winter when it decided to crash on Farrand Field for a few hours, right in the middle of CU campus. Although not exclusively nocturnal, coyotes are often active at night, but are quite adaptable, as was evidenced by this particular coyote's behavior, alive and well in the middle of campus! Note the relatively drab coloration. |
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I have a friend who is partially colorblind, about as colorblind as an elephant according to some recent studies. If you see him outside, he's going to be wearing sunglasses (unless he's done something to piss off Poseidon).*** Is he doing it just to look cool? Well, yes, I suppose that's at least partially the case. But for him, and for many other people who suffer from color blindness, it seems like they make up for it with above average night vision. Essentially, an imbalance of rods (a photoreceptor that is not sensitive to color but is sensitive to light and dark conditions and aids in night vision) and cones (a photoreceptor that is sensitive to color and less sensitive to light/dark conditions) leads to many who are color blind reporting better than average ability to see what's going on in low-lighting conditions.
When all of these seemingly disparate ideas are regarded holistically, it seems to make sense. By default, most vertebrates enjoy a wide range of color vision (sometimes even a wider range than humans!). However, during the Mesozoic dinosaurian domination, some groups of vertebrates such as the mammals were forced to take up residence during the night. For millions of years, these little creatures lived a nocturnal existence, and it seems like being able to see in color no longer proved to be a competitive advantage for them. Following the extinction of the dinosaurs and the subsequent radiation of mammals, it appears that the possession of color vision was unnecessary for them to survive and thrive. Many mammals are still largely nocturnal today (think of your kitty at home and all of her midnight memories), which might have something to do with this disparity between their rods and cones. All in all, it would appear that changes of the night can have some pretty profound effects on your ability to see across the color spectrum.
*You will probably come across them doing some serious work as well, but dinosaur taste-testing can be pretty important.
**I thought that Dr. Bakker, who I talked to a lot about this, mentioned that most or all frogs had the sclerotic ring, but I have been unable to confirm or deny this with a quick search through the resources I have at my disposal.
***Twice.
Works Cited:
Allis, T. (1849). On the Sclerotic Ring of the Eyes of Birds and Reptiles. "Proceedings" of the Yorkshire Philosophical Society. Retrieved December 4, 2014, from https://archive.org/stream/onscleroticringo00allirich/onscleroticringo00allirich_djvu.txt
Curtis, Elizabeth L., & Miller, Robert C. (1938). The Sclerotic Ring in North American Birds. The Auk, 55(2), 225-243. Retrieved December 4, 2014, from http://www.jstor.org/discover/10.2307/4078198?uid=3739568&uid=2&uid=4&uid=3739256&sid=21105375434903
Yokoyama, S. (2005). Elephants and Human Color-Blind Deuteranopes Have Identical Sets of Visual Pigments. Genetics, 335-344. Retrieved December 5, 2014, from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1449733/
I enjoyed this article, my vision at night is good, but i weak in daylight, i need to wear something to blunt the light of the sun, both my color dif sharp too, i love to draw and color my works
ReplyDeletethank so much