B is for Big

Holy cow! Or, maybe I should say Holy Brachiosaurus … or Holy Argentinasaurus…. or Holy Breviparopus….

These dudes got big!

In today’s dinosaur B-themed post, I’m going to share a little bit (and it’s already three days late and I haven’t much time, so not too much) on what, how, and why about these big-a@@ed creatures.

How Big Was Big?

Think almost half the length of a football field (American or European). The longest and largest dinosaur where much of the skeleton was discovered is either Argentinosaurus huinculensis or Patagotitan mayorum. Both of them were in a group labeled “Titanosaurs” and both were identified from bones discovered in — yep — Argentina. They ranged in length from 30 to 40 meters… about 45 yards and may have weighed around 80 tons.

As soon as you get measurements, of course, you start wondering, well, how much is that? Football fields are handy just because many people have seen them. For reference, a 757 aircraft weighs around 100 tons and is about 40 m, so visualize a living, stalking creature that looks like a giant airplane. Walking around on a football field, waving its intensely long neck around and wondering where all the veggies went. Forty meters is also the world record (officially Guinness WR) for flinging a Frisbee, so imagine throwing a Frisbee as long as a dinosaur!

The largest land creatures that lived, these dinosaurs, were part of a group called sauropods. You see saur a lot in dinosaur names, and it simply means lizard.

(Dinosaur means “terrible + lizard.” But that is a matter of perspective, isn’t it? Maybe they were “wonderful lizards,” like bonosaurs or something. Well, they were made of bone. Anyway.)

Sauropod or lizard foot referred to these giant creatures with giant feet. One of the biggest footprints ever found is in Australia–almost six feet! The feet had to be big to support giant leg bones, hip bones, bodies, neck and tail. In the earliest days of discovering dinosaur bones, they theorized that these creatures would be massive, but it was hard to visualize. Many of the earliest drawings had the big dinosaurs dragging their tail on the ground — how could they possibly support the weight — but, of course, that made no sense.

Scientists now know that the neck bones and tail bones of sauropods were relatively light weight, not quite hollow, but much lighter than comparative necks of reptiles today. The size of the footprints and leg bones also suggest solid hip bones supported by feet. That’s why today we know that dinos were not belly-crawling slitherers like salamanders or crocodiles, but instead walked upright. The meat-eaters ran around on two legs, but the sauropods had four legs, supporting them upright. It’s thought they could even rear up on their massive hind legs to reach the tops of trees, which them even taller. But not as tall as say …

But Not That Big

Here’s another reference point — Godzilla. The Godzilla that picks up subway trains and walks through power lines was about 50 m tall, which is what these sauropods might be when they stretched their neck up. The newer Godzilla that fights King Kong is twice as big, so sauropods were smaller apparently than the CGI version of Godzilla. In other words, sauropods were giant animals as tall as a city building from the 1950s and would dominate the average Main Street, but they still would be hidden when they walked through New York City. Until they started flicking the tail around through the buildings. But you’ve probably seen the Avengers movies, so you can visualize that.

One of the obvious things to note when you ask a question like “what’s the biggest dinosaur” is that there isn’t agreement. It’s controversial. Do you mean by weight? Big by height? Tail? Bone? I quickly found huge arguments on Reddit and in WordPress about the size of these dinosaurs. The good thing is that they were passionate sciency arguments, with people being not making nasty personal comments as they do when arguing about the engines on the Millennium Falcon, etc., (it made the Kessel run in 12 parsecs, you numbskull!) …but using facts to bolster their claims.

One passionate Internet science guy shared the above comparative diagram, and it seemed to be the most comprehensive of the many, many comparatives out there, so I posted it. But Breviparopus on the far right is probably wrong. They had some footprints, but not enough and found more… long story. They didn’t find any actual bones, and you do need bones. The big titanosaurs were closer to the dinosaurs in the middle there.

But note tiny, tiny human on one side, and that T rex and his meat-eating friends were quite a bit smaller than these sauropods. The meat eaters probably didn’t go after them on their own, in the same way that a lioness can’t on its own bring down an elephant. But there were plenty of babies and other smaller critters for T rex to run down.

Grow Little Dinosaur, Grow!

The next question might be how did they “get” so big? Against, that’s not quite precise enough for the scientists. One interpretation is how did they evolve to become 50 m tall? Several sites which cover this topic say it was the available of ample vegetation in the Jurassic and Cretaceous period. Very swampy, humid, lots of carbon dioxide, so plants were thriving. Yet having a lot of plants wouldn’t really make dinosaurs grow physically giant, but just provide an opportunity for the population as a whole to thrive.

The better thought is to think about that Darwin “natural selection” thing for both plants and dinosaurs. The plants competed for carbon dioxide, for space, and for sunlight. One way to compete with other plants is to grow taller and closer to the sun. That means more tall plants, which would mean the taller animals–like Brachiosaurus– could have the tasty tall trees all to themselves.

But the other way to think about growth is physically. This might be the time to mention Kristi Curry Rogers, one of the foremost experts on dinosaurs in the U.S., and in particular an expert on sauropods. In fact, I was inspired to do this series because I checked out her Great Course on “Dinosaurs,” which may be available for free at an online library near you.

In Roger’s Guidebook–cause of course there’s a guidebook and of course I have it handy for this exercise–she talks about trying to learn about how fast dinosaurs grow. Even the sauropods came out of eggs the size of “soccer balls.” How do you get from that to half a soccer field? The conventional wisdom, before Rogers and her ilk started looking in microscopes, was that sauropods might take 70 to 100 years to grow that big. But that’s not the case.

Paleontologists can look at shavings off bone and analyze these things called osteoblasts and osteoclasts, which have primary and secondary growth patterns. Visualize tree rings–that’s not what the growth looks like–but think of the ability to see speed and pattern of growth. These scientists were able to look at the bone growth markers of dinosaurs and compare them with modern animals. They could pick out which modern animals had similar-looking bone growth markers. It’s not reptiles.

The sauropods specifically had bone growth markers that were closer to birds or slow-growing mammals. Not every dinosaur grows the same way, naturally, and not even every sauropods grows the same way. Large sauropods, said Rogers, were closer to animals that grew quickly. They might put on 50 pounds a day when they’re young; they grow 50 times faster than modern reptiles. That’s how something the size of a soccer ball would be hitting the three-story ceiling of the Museum of Natural History by the time it was about 20.

Actually, the bigger takeaway from that may not be how fast the sauropods grew, but that scientists can use microscopic views of 200 million-year-old bone structures to match the characteristics of modern animals. Not just what they look like on the outside, but what they look like on the inside. That lets them draw all sorts of conclusions about what they ate, how they walked, where they lived. and how they should be categorized.

Categories are a big deal, as I’ll talk about in the next letter.