Why Were Dinosaurs So Large and Why Don't Animals of That Scale Exist Today?

iStock.com/Kirkikis
iStock.com/Kirkikis

Untorne Nislav:

Before we start, what you need to realize is that dinosaurs were definitely large, but not so large. You probably know the numbers: the largest land mammals ever are around 6–8 meters long (19-26 feet), while the largest dinosaurs were … is it 40 meters (131 feet)?

Damn, what a number!

However, numbers can be veeeery misleading. Look at the second-largest land mammal ever, Indricotherium, and one of the largest dinosaurs, Brachiosaurus, here.

The difference seems to be incomparable …

However …

Those are two entirely different body shapes: most of the brachiosaur's length is used up by its enormous neck and tail. To make it fair, I want you to use your two thumbs: place one over the dinosaur’s neck, and the other over the tail (hopefully, you are not reading this from a touchscreen).

And suddenly, enormous becomes quite … normous. Obviously, Brachiosaurus is still larger than Indricotherium, but it's not four times larger like the numbers would suggest. The real, fair difference between the two is roughly the same as the difference between an elephant and a hippo:

An elephant behind a number of hippos near the water.
iStock.com/JurgaR

Moral of the story: don't let the body shape mislead you.

So here's the answer to the "so large" part of your question: because they weren't.

However, there is still some "true" difference in size to account for. And at least two factors could've contributed to it:

1) Different rules of herbivory.

In the age of mammals, the most effective strategy of herbivory is grazing.

A large herd of wildebeests in a field.
iStock.com/WLDavies

Grasslands are super-effective. The two most productive mammal-dominated ecosystems ever are savannas and (now gone) mammoth steppes: both can feed enormous numbers of huge mammals. With grasses growing at insane rates everywhere, no other food source on Earth can provide for such high mammalian biomasses.

Moral of the story: if you want to grow up big and full, eat grasses.

However, it wasn't always so. In times of dinosaurs, grasses didn't exist. So, the largest animals then were forced to resort to the second-best herbivory strategy: browsing.

image of a brachiosaurus eating leaves from a tree
iStock.com/MR1805

Tree foliage doesn't grow like grasses, yet still there's usually a considerable amount of it per area unit, because it overlaps vertically many times.

Dinosaurs that fed from canopies could afford to grow large: for thermoregulation or defense from predators—usual reasons.

However …

Any animal that grows too big inevitably experiences difficulties with food. At present, any herbivore that became too large would likely just move onto grasses. But dinosaurs couldn't. Hence, the only solution that they had was to grow necks even longer to get even more foliage. But if you grow a larger neck, you also need a larger tail (for balance). Then, you also need broader and thicker bones for all those muscles to attach, stronger legs to support the extra tons of weight, and so on and so on.

Effectively, it was a dead loop: dinosaurs became large, then they grew longer necks to support the growing need for food, which in turn made them become even larger, which in turn further increased their need for food. Browsing herbivory was likely the driving force of sauropod size, and in the end, the only limiting factor was probably the height of the highest canopy.

2) Reproductive limitations

This one doesn't really answer the "why sauropods were large?," but the "why mammals aren't that large?".

A typical sauropod was, effectively, a reproductive frog. It laid dozens if not hundreds of small eggs that hatched into very small babies that had little to do with adults: they occupied very different niches and fed on different food. For sauropods, it killed two problems: firstly, it made pregnancies easy and unnoticeable (which is a factor when you weighed 60 metric tons), and secondly, it removed competition for food between adults and babies.

In other words, sauropods could afford to become as large as necessary without worrying much about how it would affect their pregnancy and reproduction.

On the contrary, being a pregnant 60-tonne (66-ton) mammal is a nightmare—of a real and deadly kind.

All (placental) mammals bear relatively large offspring. However, if you weighed 60 tonnes, that would be … what, 2 tonnes (4400 pounds) heavy offspring? Carrying extra 10 kilograms (22 pounds) of weight at the peak of pregnancy is difficult enough for humans, but having to carry 10 extra tonnes (22,000 pounds) is just impossible, unless you are a whale and swim.

Not to mention that it would be a very long pregnancy.

Not to mention that pregnant females require even more food.

Not to mention that the young must be fed, only to grow up to compete with you for the same food later.

Moral of the story: children are expensive … unless you are a frog or a sauropod.

Q: How about livebearing smaller babies?

There are two problems with this. Firstly, it just doesn't happen. There are relatively small newborns in some placental mammals, but nothing like the difference between sauropod adults and babies.

Secondly, if babies are too small, then they become unavailable for social interactions: in fact, they are better to stay away from parents immediately to avoid being stomped on. Social behavior and learning are the backbone of mammalian success. Trying to get rid of it just isn't worth it.

So in the end, dinosaurs that weren't so large were large because they bred like frogs and because their kitchen was … a little underrepresented.

This post originally appeared on Quora. Click here to view.

In What Field Was Dr. Martin Luther King Jr. a Doctor?

Express Newspapers/Getty Images
Express Newspapers/Getty Images

Martin Luther King Jr. earned a doctorate in systematic theology from Boston University in 1955. He’d previously earned a Bachelor of Arts from Morehouse College and a Bachelor of Divinity from Crozer Theological Seminary. His dissertation, “A Comparison of the Conception of God in the Thinking of Paul Tillich and Henry Nelson Wieman,” examined the two religious philosophers’ views of God in comparison to each other, and to King’s own concept of a "knowable and personal" God.

In 1989, some three decades after King had earned his doctorate, archivists working with The Martin Luther King Papers Project discovered that King’s dissertation suffered from what they called a “problematic use of sources.” King, they learned, had taken a large amount of material verbatim from other scholars and sources and used it in his work without full or proper attribution, and sometimes no attribution at all.

In 1991, a Boston University investigatory committee concluded that King had indeed plagiarized parts of his dissertation, but found that it was “impractical to reach, on the available evidence, any conclusions about Dr. King's reasons for failing to attribute some, but not all, of his sources.” That is, it could have been anything from malicious intent to simple forgetfulness—no one can determine for sure today. They did not recommend a posthumous revocation of his degree, but instead suggested that a letter be attached to the dissertation in the university library noting the passages lacked quotations and citations.

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Who Is 'The Real McCoy'?

Inventor Elijah McCoy is may or may not be "The Real McCoy."
Inventor Elijah McCoy is may or may not be "The Real McCoy."
Ypsilanti Historical Society, CC BY-SA 4.0 via Wikimedia Commons

After taking a cool, carbonated sip of champagne from the Champagne region of France, you might say, “Ah, now that’s the real McCoy.” Sparkling wine from anywhere else is technically just sparkling wine.

The phrase “the real McCoy,” which can be used to describe any genuine version of something, has several possible origin stories. And while none of them mention champagne, a few do involve other types of alcohol.

According to HowStuffWorks, the earliest known recorded instance of the saying was an 1856 reference to whisky in the Scottish National Dictionary—"A drappie [drop] o' the real MacKay”—and by 1870, a pair of whisky distillers by the name of McKay had adopted the slogan “the real McKay” for their products. As the theory goes, the phrase made its long journey across the pond, where it eventually evolved into the Americanized “McCoy.”

Another theory suggests “the real McCoy” originated in the United States during Prohibition. In 1920, Florida-based rum runner Bill McCoy was the first enterprising individual to stock a ship with alcohol in the Caribbean, sail to New York, and idle at least three miles offshore, where he could sell his wares legally in what was then considered international waters. Since McCoy didn’t water down his alcohol with substances like prune juice, wood alcohol, and even turpentine, people believe his customers started calling his top-notch product “the real McCoy.” There’s no definitive proof that this origin story is true, but The Real McCoy rum distillery was founded on the notion.

There are also a couple other leading theories that have nothing to do with alcohol. In 1872, inventor Elijah McCoy patented a self-regulating machine that lubricated parts of a steam engine without the need for manual maintenance, allowing trains to run continuously for much longer distances. According to Snopes, the invention’s success spawned a plethora of poor-quality imitations, which led railroad personnel to refer to McCoy’s machines as “the real McCoy.”

Elijah McCoy’s invention modernized the transportation industry, but he wasn’t the only 19th-century McCoy who packed a punch. The other was welterweight champion Norman Selby, better known as Kid McCoy. In one story, McCoy decked a drunken bar patron to prove that he really was the famous boxer, prompting others to christen him “the real McCoy.” In another, his alleged penchant for throwing fights caused the press to start calling him “the real McCoy” to acknowledge when he was actually trying to win. And yet another simply suggests that the boxer’s popularity birthed so many McCoy-wannabes that Selby started to specify that he was, in fact, the real McCoy.

So which “the real McCoy” origin story is the real McCoy? The 1856 Scottish mention of “the real MacKay” came before Elijah McCoy’s railroad invention, Kid McCoy’s boxing career, and Bill McCoy’s rum-running escapades, but it’s possible that the phrase just gained popularity in different spheres at different times.

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