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| Jlhopgood, CC BY-ND 2.0 (adjusted). |
Birds evolved from dinosaurs 165 million to 150 million years ago. Of all the birds in the world, the one that shares the most DNA with the ancestor of all birds is…the chicken! This means that the closest living relative of the dinosaurs is the chicken.
But that doesn’t mean Tyrannosaurus rexes tasted like chicken, which is unfortunate since the Kentucky-fried drumstick would have been larger than you are. Taste is determined by other factors, such as what the animal ate and how much fat is in the meat. Those using their muscles slowly for extended periods (like cows and most larger animals) have red meat, while those who used them twitchily for short periods (like cheetahs, chickens and most smaller animals) would have white meat. Contrary to popular opinion, pigs and humans have red meat. But more to the point, predators, and scavengers tend to taste gamey. T. Rex was both, so would have had very strong-tasting red meat. But some smaller vegetarian dinos may have tasted like chicken.
The chicken or the egg?
Also, if anyone asks you which came first, the chicken or the egg, say “the egg”. Eggs have been around for about 600 million years, while chickens have only existed for about 10,000 years. All female vertebrates have eggs. The earliest external eggs with shells evolved in diapsids, an ancestor of reptiles, roughly 350 million years ago. Our synapsid ancestor split off not long before this from the shared ancestor of mammals, reptiles, and birds. All of the subsequent dinosaurs laid eggs, so the egg came before them as well.
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| Fossilized dinosaur eggs. Gary Todd. |
Hard-shell eggs are important because it allows reptiles and birds to live completely on land, while the older amphibians are still tied to water for laying their eggs. It’s the same for the few fish that are able to live out of the water, like mudskippers.
Looking at the question from the point of view of an individual chicken, then again that chicken’s egg came first. If you look at it metaphorically, this conundrum is intended to point out the futility of trying to determine the cause of self-perpetuating cycles. It can be puzzling at first, but ultimately fails because the cause can be determined.
If you change the question to, “which came first, the chicken or the chicken egg?” then it becomes a bit tricky because you can’t have a chicken egg unless you have a chicken. The problem then becomes was there a first chicken? Animals are constantly evolving, going through intermediate stages before they gain the set of features that taxonomists use to determine whether an animal is a new species.
It’s all a bit messy because taxonomy tries to force animals into artificial categories. Before the chicken, there was a bird classified as something else, and as it evolved into a chicken there would have proto-chickens, or those who were partially ancestor and partially chicken. There isn’t a clean break between the two. You don’t have a situation where the parent is not a chicken, but the offspring are.
But for the sake of argument, let’s just say there was one particular feature that suddenly evolved that made one individual a chicken. Then its egg would have come from a non-chicken, but it’s the egg that the chicken embryo developed in, so which would it be? Either the non-chicken laid a chicken egg or the chicken developed in a non-chicken egg. The answer depends on the features of that particular egg, so we’ll never know. It would have had to have been caused by a single DNA mutation, but evolution usually works gradually over the course of many mutations, so there probably a first chicken.
To explain this in another way, there are salamanders in California that live around most of a lake. They live on the north and south sides and are one continuous community that connects along one side of the lake. Those in the north look different from those in the south and the two won’t breed with each other, but the community breeds all the way along the lake.[1]
Are they two species or one? Or are they in the process of becoming two species? Because of the connection along the side, they’re still considered to be one species, but if that connection is broken, the middle salamanders will become one or the other and there will be two. It’s isolation that usually causes a species to gradually separate into two, but the key is “gradually”. It doesn’t usually happen overnight.
Taxonomy is a very useful tool, but it has its flaws and you can’t fit nature into pigeonholes. The flaws become much more apparent when you look back in time, since lineages of animals blend into one another, which is why looking for “missing links” doesn’t make sense. All animals are links on the way to becoming something else—unless they go extinct. What that something else is will depend on how taxonomists decide to pigeonhole animals in the future.
Getting back to chickens and dinosaurs: While chickens are the dinosaurs’ closest living relatives, the few available fossils suggest the earliest birds looked more like a loon, but honked like geese.[2]
And one last thing, there are now 22 billion chickens on the planet, so they outnumber us three to one. On the other hand, people are working hard to eat as many of them as we can.
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[1] Robert A. Wallace, Jack L. King, and Gerald P. Sanders, Biology: The Science of Life, Glenview, IL: Scott, Foresman & Co., 1981, pp. 388-90.
[2] Jeff Hecht, “Goose-like birds survived the dino wipeout”, New Scientist, no. 3149, October 28, 2017, p. 9, and a longer version as “Geese-like birds seem to have survived the dinosaur extinction”, https://www.newscientist.com/article/2151059-geese-like-birds-seem-to-have-survived-the-dinosaur-extinction/, citing Federico L. Agnolín, Federico Brissón Egli, Sankar Chatterjee, Jordi Alexis Garcia Marsà, and Fernando E. Novas, “Vegaviidae, a new clade of southern diving birds that survived the K/T boundary”, The Science of Nature, vol. 104, p. 87, October 7, 2017, https://dx.doi.org/10.1007/s00114-017-1508-y.
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