In the question posed by Andrew Murphy, April 8/94, he asked about the size of dinosaurs, and posited that gravity may have been a factor. Though the question was poorly worded, the gravity part wasn’t answered in Cecil’s reply, and I am curious if there is any serious scientific merit to the idea that gravity was less strong during the time of the dinosaurs. I have read that the largest land animals, elephants, are at the upper limit of the possible size a land animal could be and still move around effectively; and the largest flying birds, the eagle, can’t grow much bigger than 25lbs (I think, maybe it was kg?) and still be able to fly, so how otherwise could a creature attain the size and shape of a dinosaur like the apatosaurus? (I may have gotten the bird species wrong)
Hi, scule, and welcome to the SDMB.
Just for future reference, it’s customary to provide a link to the column you are referring to.
It appears to be this one:
http://www.straightdope.com/classics/a4_088.html
The question about gravity was accurately and fully answered, although in typical Cecil fashion. You do have to be looney tunes to take it seriously (or the notion that the earth was spinning fast enough to counteract gravity).
There is not the slightest evidence in the geologic record that would support such any such thing.
Obviously, whoever told you that elephants were the largest possible land animals had it wrong. Large dinosaurs have been shown to be elegantly constructed animals, well-adapted to their environments. The true supersized ones probably didn’t move very quickly but they would have to be nomadic to support their enormous food needs and so they moved whenever they needed to.
The biggest winged dinosaurs had enormous wingspans with small, light bodies. I’m not sure they were ever capable of true flight. If they were mainly gliders than they could support larger wings than true flying modern birds.
A surprising amount has been learned about dinosaurs even since 1994. I’d check around the library for a good and new book about them.
There are many dinosaur lovers around here who will be sure to come by in a moment.
Of course, those of us who have read Robert J. Sawyer’s book End of an Era know the real reason dinosaurs were able to get so big: Gravity-suppressor satellites built by Martian virus-blobs to make Earth habitable for them.
Welcome to the SDMB, and thank you for posting your comment.
Please include a link to Cecil’s column if it’s on the Straight Dope web site.
To include a link, it can be as simple as including the web page location in your post (make sure there is a space before and after the text of the URL).
Cecil’s column can be found on-line at the link provided by Exapno Mapcase, our russian marxist brother.
The column (including Slug Signorino’s illustration) can also be found on pages 88-90 of Cecil Adams’ book «The Straight Dope Tells All (1998)».
moderator, «Comments on Cecil’s Columns»
I knew there was a reason I don’t read Robert Sawyer.
Heh heh … it’s actually a lot less corny than it sounds. Robert Sawyer is one of my top three favorite sci-fi authors of all time. I highly recommend Calculating God and The Terminal Experiment for new readers of his books.
The classic answer was that dinosaurs were “cold blooded” (actually ectothermic, or heated from without) and that they became large to retain heat better. Many now doubt this.
Another slightly off the wall theory (but nowhere near as radical as suggesting that gravity has altered) was that in the Mesozoic, the Earth’s atmosphere was richer in oxygen than it is today, boosting the energy available to allow creatures to grow larger. But most geologists insist that the oxygen content of the atmosphere has remained nearly constant.
Of course you could also ask why not just dinosaurs, but lots of other prehistoric animals were very large. Indiritherium (also known as Baluchitherium) was larger than any mammoth or elephant that ever lived, as big as some sauropod dinosaurs. And fossils of giant dragonflies and other insects date from early times.
Probably there are several reasons why so many prehistoric creatures were larger than any comparable specimen today:
-Lack of competition/ predation: Giant dragonflies existed before birds, bats and other flying insect eaters had appeared. They would be at a disadvantage today. Giant tortoises used to grow as big as small cars, because they were effectively immune to predation; that is, until a certain primate developed the spear.
-Available ecospace: animals have to maintain a certain minimum viable population. The larger each animal is, the more food and room the species needs to sustain itself. There’s a strong link between the total habitat available to a species and the maximum size the members of it can attain. In the Mesozoic the Atlantic had not yet split the Americas from Africa and Asia, so the dinosaurs had an enormous unified landmass to inhabit.
-Recent extinctions: The ice ages of the last million years were extremely rough on animal life in the northern hemisphere. Gigantism is a specialization that tends to appear when the climate has remained stable and dependable for many millions of years. A die off about 10,000 years ago finished off the mammoths, saber-tooth cats, giant ground sloths, and many others. This could have been caused by climate change associated with the end of the last glacial period, the expansion of humans, or both. What we see today in the animal kingdom are the survivors of the last extinction, and in rough times small and fecund tends to survive better than bigger but fewer.
Large animals have advantages over smaller ones: They can take food away from competitors, they can take mates away from competitors, they can fight off predators. They are more likely to survive and have offspring. Animals will grow as large as their particular environmental niche allows.
By the way, the largest animals ever are the great whales.
Mammals were well on their way to following the dinosaur’s gigantism until that pesky ape came along and learned how to kill even the largest animals. Even the whales.
Thanks for the replies. I’ll admit, my interests generally lie along public health and human history lines, as opposed to animal biology or dinosaurs, but I had heard the argument about dinosaur sizes before used as a tool of creationists - which I am NOT - to explain why science is wrong. (As an aside, I just love the way they try to use science to explain why science is wrong). I just wanted to make sure I got the right facts (and I know the blue whle is the largest animal ever, but I was referring to land animals)
Dinosaurs got so big from eating so much junk fast-food. The dinosaur governments and doctors all put out warnings about how dinosaurs were getting obese, but did they listen? Oh, no, not when there were McDino’s and Kentucky Fried Pterosaur and Burger T-Rex and all the rest of them fast-food chains.
How did pterosaurs get off the ground? Were they SOL if they landed anywhere but near a cliffside?
-k