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.

Is There An International Standard Governing Scientific Naming Conventions?

iStock/Grafissimo
iStock/Grafissimo

Jelle Zijlstra:

There are lots of different systems of scientific names with different conventions or rules governing them: chemicals, genes, stars, archeological cultures, and so on. But the one I'm familiar with is the naming system for animals.

The modern naming system for animals derives from the works of the 18th-century Swedish naturalist Carl von Linné (Latinized to Carolus Linnaeus). Linnaeus introduced the system of binominal nomenclature, where animals have names composed of two parts, like Homo sapiens. Linnaeus wrote in Latin and most his names were of Latin origin, although a few were derived from Greek, like Rhinoceros for rhinos, or from other languages, like Sus babyrussa for the babirusa (from Malay).

Other people also started using Linnaeus's system, and a system of rules was developed and eventually codified into what is now called the International Code of Zoological Nomenclature (ICZN). In this case, therefore, there is indeed an international standard governing naming conventions. However, it does not put very strict requirements on the derivation of names: they are merely required to be in the Latin alphabet.

In practice a lot of well-known scientific names are derived from Greek. This is especially true for genus names: Tyrannosaurus, Macropus (kangaroos), Drosophila (fruit flies), Caenorhabditis (nematode worms), Peromyscus (deermice), and so on. Species names are more likely to be derived from Latin (e.g., T. rex, C. elegans, P. maniculatus, but Drosophila melanogaster is Greek again).

One interesting pattern I've noticed in mammals is that even when Linnaeus named the first genus in a group by a Latin name, usually most later names for related genera use Greek roots instead. For example, Linnaeus gave the name Mus to mice, and that is still the genus name for the house mouse, but most related genera use compounds of the Greek-derived root -mys (from μῦς), which also means "mouse." Similarly, bats for Linnaeus were Vespertilio, but there are many more compounds of the Greek root -nycteris (νυκτερίς); pigs are Sus, but compounds usually use Greek -choerus (χοῖρος) or -hys/-hyus (ὗς); weasels are Mustela but compounds usually use -gale or -galea (γαλέη); horses are Equus but compounds use -hippus (ἵππος).

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

Can Soap Get Dirty?

iStock/vintagerobot
iStock/vintagerobot

When you see lovely little bars of lemon-thyme or lavender hand soaps on the rim of a sink, you know they are there to make you feel as fresh as a gardenia-scented daisy. We all know washing our hands is important, but, like washcloths and towels, can the bars of hand soap we use to clean ourselves become dirty as well?

Soaps are simply mixtures of sodium or potassium salts derived from fatty acids and alkali solutions during a process called saponification. Each soap molecule is made of a long, non-polar, hydrophobic (repelled by water) hydrocarbon chain (the "tail") capped by a polar, hydrophilic (water-soluble) "salt" head. Because soap molecules have both polar and non-polar properties, they're great emulsifiers, which means they can disperse one liquid into another.

When you wash your dirty hands with soap and water, the tails of the soap molecules are repelled by water and attracted to oils, which attract dirt. The tails cluster together and form structures called micelles, trapping the dirt and oils. The micelles are negatively charged and soluble in water, so they repel each other and remain dispersed in water—and can easily be washed away.

So, yes, soap does indeed get dirty. That's sort of how it gets your hands clean: by latching onto grease, dirt and oil more strongly than your skin does. Of course, when you're using soap, you're washing all those loose, dirt-trapping, dirty soap molecules away, but a bar of soap sitting on the bathroom counter or liquid soap in a bottle can also be contaminated with microorganisms.

This doesn't seem to be much of a problem, though. In the few studies that have been done on the matter, test subjects were given bars of soap laden with E. coli and other bacteria and instructed to wash up. None of the studies found any evidence of bacteria transfer from the soap to the subjects' hands. (It should be noted that two of these studies were conducted by Procter & Gamble and the Dial Corp., though no contradictory evidence has been found.)

Dirty soap can't clean itself, though. A contaminated bar of soap gets cleaned via the same mechanical action that helps clean you up when you wash your hands: good ol' fashioned scrubbing. The friction from rubbing your hands against the soap, as well as the flushing action of running water, removes any harmful microorganisms from both your hands and the soap and sends them down the drain.

This story was updated in 2019.

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