Why the hell did Dinosaurs get so big? How could they? Wouldn’t it be impossible given Galileo’s square-cube law?
In what has become known as the dinosaur paradox, a few key issues have plagued scientists.
- Inadequate bone strength to support the largest dinosaurs
- Inadequate muscle strength to lift and move the largest dinosaurs
- Unacceptable high blood pressure and stress on the heart of the tallest dinosaurs
- Aerodynamics principles showing that the pterosaurs should not have flown
I’m only going to focus on number two, as this is the most relevant to what we do here on this blog. (If you want to read more about why dinosaurs were able to get so big, you can read my post at my other blog: sapien games.)
Sometimes (often) in science, something that at first appears to be a “paradox” is in fact not one at all. Instead, the original facts of that case were simply misunderstood. And once the facts become clear, the one-time paradox fades away.
In worst cases, these facts were misunderstood simply because scientists in different fields don’t pay nearly any attention to what others scientists are doing in other fields. Something of that sort is happening here.
Here is a paragraph from the article on the dinosaur paradox at dinosaurtheory.com:
The relative bone strength and the relative muscle strength are grouped together because they are similar scaling problems. For both, strength is function of the cross-sectional area. If we look at the longest length of a bone or muscle and then imagined cutting this length in half, the newly exposed area is the cross-sectional area. The strength of either a bone or a muscle is directly proportional to this cross-sectional area, so both bone and muscle strength are two dimensional attributes. Yet body mass is a function of volume, a three dimensional attribute. In accordance to the Square-Cube, as we look at increasing larger animals the mass of each animal increases at a faster rate than the cross-sectional areas of either the bone or the muscle. Thus, larger animals have less relative muscle strength and less relative bone strength than that of smaller animals.
The bold is mine – these statements are false.
Any undergrad in exercise science would know that strength is NOT directly proportional to muscle cross-sectional area, but a professional paleontologist might not. This is not to disparage the paleontologist (there is plenty of info in their field that exercise sci people wouldn’t know). But, sometimes this lack of understanding can lead to paradoxes that aren’t paradoxes.
To most people, when they see a big bodybuilder, they assume that they must be one of the strongest men on the planet. After all, they LOOK strong. They are so big; they have so much muscle. The top pro bodybuilders are literally the most muscular men to have ever walked the earth. But, they are decidedly NOT the strongest.
The cold-hard truth is that the size of muscle is NOT directly proportional to strength and is therefore not a 2-dimensional attribute. (That is, when size goes up strength goes up and vice versa – think of a simple Cartesian graph.) It IS true that as mass goes up it becomes harder to be as relatively strong. But, does that mean that dinosaurs weren’t strong enough to hold themselves up? No.
When it comes to building strength, we can call muscle size (it’s cross sectional area) the “weak” force. And we can call motor unit activation and fiber types the “strong” forces. All of which are more complex than you might expect.
The statements above are predicated on a single fallacy of both science and logic. It goes something like this:
Statement A: Strength goes up if and only if muscle size goes up
This statement is really the conjunction of two statements:
A1: If Strength goes up, then muscle size goes up.
A2: If muscle size goes up, then strength goes up.
Let’s start with A2.
It IS true in a weak sense that if muscle size goes up, then strength goes up. But, not as much as one would think.
The size of muscle is dictated by a lot of things, among them being contractile proteins and sarcoplasm. Contractile proteins are the little guys that actually do the mechanical work of moving your body around. The sarcoplasm is the fluid in your muscle cells. Believe it or not, the size of your muscle has as much to do with how much “water weight” you’re carrying as it does with how many contractile proteins you have. Yes, more sarcoplasm does correlate with more strength, but not as highly as with more contractile proteins.
Even with a “maximum” amount of both of these, this still doesn’t mean you will be as strong as someone half your size.
Which leads me to A1.
The first of the strong forces is much more complicated, and it is at least part of what accounts for the fact that top middleweight powerlifters and olympic weightlifters are SIGNIFICANTLY stronger than the worlds top bodybuilders, in spite of the fact that they are half their size.
Just because you have (for the sake of argument) 10 muscle fibers, doesn’t mean that you use all 10 every time you do something. In fact, most people won’t be able to activate all 10 even in their moments of greatest need (like when lifting a really heavy weight). The reason is that the body is all about efficiency. Using all of your muscle fibers all at once is taxing as hell. This is why the more advanced you get in strength sports, the longer your rest periods have to become, because you’ve literally worked harder than someone who is just beginning can possibly work.
What we’re saying here is that it is perfectly possible to get a whole lot stronger without ever getting much bigger, simply by training your muscles to actually work at the top of their capacity.
OK … is that it? Nope.
We also have the difference in fiber types. There are lots of them (and the list seems to get bigger every decade), but to keep things simple as all hell, we’ll just go with two groupings of them: fast twitch fibers and slow twitch fibers.
The fast twitch fibers are the ones you use when you want to go … fast (surprised?), and the slow twitch fibers are better at going the distance. The fast ones are more efficient at bursts of energy that result in both speed and strength. The slow twitch ones are more efficient at avoiding burnout.
So if you go for a long hike up a mountain, you’d better hope you have an abundance of slow twitch fibers in your legs so that it doesn’t burn the whole way! (Trust me, I hate hiking for a reason …)
Now imagine two ladies, each with identical cross-sectional area of muscle in their thighs. But one has an over abundance of fast twitch fibers and the other has an over abundance of slow twitch fibers. They are the same size, but the first is going to be a ton stronger.
There’s more to all of this, of course, including the neuromuscular coordination problem and the importance of leverage as dictated by limb-length, tendon and ligament attachment points, etc; but, I’m not even going to get into that.
The “paradox” regarding dinosaur size includes statements about the lack of muscle strength adequate enough to support their weight. But, this assessment is based solely on the myth of Statement A, above. Clearly, that statement is false.
OK, I know what you’re thinking, “Nick, for heaven’s sake! You’re talking about mammals, and humans particularly. The author above is talking about dinosaurs! OMG!”
But, hear me out.
We have NO fossilized evidence of what the muscles of dinosaurs were like. So, speculation based upon available current animals is all we have. Further, we DO know that dinosaurs are closest related to modern-day birds, and bird muscles function in the same way as ours. That is, among animals, a muscle is a muscle in the broad sense, and species “pick” which configuration they can most use from the available options (as discussed above). (Well, natural and sexual selections “pick” for them.)
We also know that these beasts DID exist, and they WERE huge. So, clearly they were able to stand up and hold their own weight. Part of the many reasons (see here for more) that they were able to do this is likely because of a muscle-configuration-distribution that made that possible. We know that Statement A is false with regards to mammals, and by Occam’s Razor, it was probably false for dinosaurs.
They had big legs, but they also must have had strong legs – not the same thing.