Category Archives: Dinosaur

Giants in a Giant World: Why Were Dino’s So Darned Big?

Brontosaurus-Triceratops

Dinosaurs were big, some of them were monstrous.  But, how is that even possible?  Aren’t there natural constraints on size that prevent our own big mammals from getting to the size of buildings?

There are a few key problems that have contributed to what is known as the Dinosaur Paradox.

Cromercrox tries to hash it out:

First, the digestion …

Sauropods swallowed enormous amounts of low-quality food that simply composted in their enormous bodies. The food wasn´t processed in the complex ways seen in ruminants or rabbits – it just went in the thin end, down to the thick middle, and took a long time to digest. As every gardener knows, the best and most efficient compost heaps are also the largest, so large gut volume combined with an active microflora and long retention times means an emphasis on size. Sauropods were gigantic walking compost heaps. (And I bet they farted like anything).

But wait, there´s more.

Indeed there is.  As I mentioned in an early article on whether dinosaurs were warm blooded, the lungs that these beasts had are quite different than ours (and other mammals).  Basically, they have the lungs of birds – air sac lungs.  These would have aided in the expelling of the enormous amount of heat generated by the fermentation process we talked about above.

Unlike mammals, which have a simple set of lungs that pulls air in and expels carbon dioxide, birds have a complex series of air sacs, accessory to the lungs, which penetrate many parts of the body, including the bones. At least some dinosaurs are known to have similar arrangements. The apposition of air sacs to the surfaces of the gut in sauropod dinosaurs would have allowed for the transfer of terrific amounts of excess heat, dumped through to the wet surfaces of air-sac membranes and converted into water vapour. Another constraint on size, lifted.

The last reason sited for their excessive size is reproduction.  Unlike the modern form of large animals like elephants and hippos, dinosaurs laid eggs.  This meant that it was easy to create new ones.

Sauropods were hard to kill not just because they were big, but because replacing them was relatively easy  – just lay a pile more eggs and bury them, the work of a moment, rather than incurring the energetic and temporal costs and life-historical limitations of gestation. Another constraint lifted – sauropods could grow bigger in a given environment, because making more of them was easier; they fed full-time on low-quality browse which they took time to digest (another incentive to grow larger) without having to chew it (ditto) and because of their bird-like structure, they were good at dissipating excess heat (the same) and were relatively lightly constructed (the same again, with a bag of crisps, please).

Bada-bing, bada-boom!  You get big-ole dino’s roaming the earth.

What he didn’t mention was that the earth had a far thicker atmosphere during this time.  In fact, during the time of the Mesozoic it is often compared to the thickness of water! Sure, it would feel different because air is not water. But, the thickness would be similar. While this could not account for all of the size issues (as even with the buoyancy of water, the shear size of these guys was still ridiculous), when combined with the above data, it helps to explain how the biggest of the biggest got so darn big.

Bloggosaurus vs. the Science-TV Megalodon


Just this last week, the Discovery Channel was playing a documentary called “Clash of the Dinosaurs.”  I was too busy to watch it, but now it looks like I should wait to get it off Netflix when the DVD comes out. Why? Read on …

Carl Zimmer relays a heartening story about a little science-blogger that could. 

Matt Wedel, a paleontologist, has been blogging about his experience with a television show on the Discovery Channel called Clash of the Dinosaurs. It didn’t go well. The producers edited Wedel’s interviews to turn his words around 180 degrees. For example, remember that old notion of big dinosaurs having a second brain along their spinal column? Not true! Wedel explained this, but if you tune into the show, you see Wedel essenitally saying, True!

Thankfully the show eventually responded favorably.  But, Unfortunately, only after the show had aired.  Apparently the DVD version will contain more actual facts, and not just hype.

Science shows are getting better and better in a few ways.  And they are getting very bad in others.  On the one hand the image quality, and excitement level, is through the roof.  And the CGI is amazing (dino’s really do look like dino’s … I think).  This is all good, since getting people excited about science has been a major struggle since the days when Plato was forced to use puppets to keep Aristotle entertained.  (OK, I made that up.  But, I wouldn’t put it past him!)

The bad thing is that science TV shows have become so mainstream that they are now forced to deal with what every other TV show has had to deal with:  advertising dollars.  These shows are getting more expensive to produce, and they have bills to pay.  They have to make sure that people will be excited enough to keep watching.  So, accuracy is degraded, or completely dumped. 

But today the story has another ending. Wedel now reports that someone from the Discovery Channel called him up and is going to make things right. I can only guess that blogs do actually make a difference some of the time. Or maybe just this once.

Probably just this once.  But, I am not that worried about it all.  In the end, we can’t be relying on entertainment TV to educate the public.  All it can do is wet the appetite. 

Chinese Brachiosaurs

Everything Dinosaur has a post on the Chinese cousin of the American and African Brachiosaur.

In a paper published in the scientific journal Proceedings of the Royal Society Biology, the Chinese researchers describe the fossilised remains of a member of the Brachiosauridae family.  The fossils were found in the Yujingzi Basin in northwestern Gansu Province, in strata dated to the mid Cretaceous, approximately 100 million years ago.  The Chinese team comment on the notion that many palaeontologists believe that the Sauropods went into relative decline during the Cretaceous, after their heyday in the Jurassic with the Ornithopods becoming more diverse and numerous.  However, a number of new Sauropod species have been discovered in Cretaceous sediments, so perhaps this particular type of dinosaur was more common in the Cretaceous than previously thought.

The animal has been named Qiaowanlong kangxii (we think the name is pronounced something like chi-oh-wan-long kang-zee), it was relatively small for a Brachiosaur with an estimated length of 12 metres, standing 3 metres tall and weighing perhaps as much as a bull African elephant.  The name refers to the Qing Dynasty emperor called Kangxi but also includes the Chinese for “bridge”, “bend in a stream” and “dragon” references to the fossil site and a dream the emperor is supposed to have had.

Dino Growth Rates on Predation

From Paleoblog:

With long limbs and a soft body, the duck-billed hadrosaur had few defenses against predators such as tyrannosaurs. But new research on the bones of this plant-eating dinosaur suggests that it had at least one advantage: It grew to adulthood much faster than its predators, giving it superiority in size.

Hungry Hungry T-Rex!

Lord knows if there are two things I love, it’s dinosaurs and eating meat!  Thankfully, over at Afarensis they’ve brought the two together for me with a post on the Taxonomy of Carnivorous Dinosaurs.

Were Dinosaurs Warm Blooded?

During the 1990’s there was a lot of discussion (yelling?) over the question of whether or not Dinosaurs were endothermic, that is, warm blooded. In the regular media there is still a pretty solid leaning toward the idea that they were.

I’m inclined to say they weren’t. Here are two reasons why:

Turbinate Bones

Endothermic (warm blooded) animals have a problem: water loss. In an effort to maintain a constant body temperature (in contrast to cold blooded animals who “go with the flow” of the ambient temperature outside), their metabolisms (the sum total of all chemical reactions in an organism) must run at a breakneck speed nearly all the time–at least in contrast to cold blooded animals (elephants have a rather low metabolism for a mammal, but still higher than a croc). One biproduct of this is water, H2O. Why?

6CH^2O + 6O^2 \rightarrow 6H^2O + 6CO^2 + Energy

The above equation is a basic cellular respiration equation (metabolism). If you put in six Carbohydrates and six Oxygens you get out six water molecules plus six molecules of Carbondioxyde plus energy (usually in the form of heat and ATP, the energy molecule).

The CO2 loss isn’t a big deal, you just breath it out. Much of the water you lose is through your urine, but you lose some water through breathing out also. This is how you can fog up your windows in the winter.

A Turbinate bone is used to reduce this water loss through your nose. How does it work? Well, in short, it is covered in specialized tissues that are responsible for humidifying, filtering, and heating the air you breath. (it does much more, but we’ll leave it at that for now).

[As a side note, if you sleep with your mouth open, thereby bypassing your turbinate bone in your nose for breathing, you’ll dehydrate more during sleep than if you sleep with your mouth closed–of course, there is the snoring problem].

Mammals and Birds both have these bones. All warmblooded species alive today infact, that have been studied for such things, have a turbinate bone to prevent excessive water loss.

Did dinosaurs have a turbinate bone? No. None of the fossils that have been collected have had them. This is strong evidence against the likelyhood of endothermy.

Climate

The second piece of evidence is in the climate of the era during which dinosaurs lived and evolved. Particularly two things: Oxygen levels and temperature. The late Triassic and Jurassic periods were both warmer (by a lot) than today and had much lower oxygen levels. We’ll cover the temperature problem first since it’s the key.

Being an endotherm in a hot environment is not easy. It’s even harder for a large creature like a big dinosaur because of a quirk of physics called the volume to surface-area ratio.

If you’re small, like a mouse, you have a large surface area relative to your overall volume. This makes heat transfer to and from the environment easy. Too easy sometimes! Rats and mice have blazing fast metabolisms because they need massive amounts of heat to be generated to maintain body temperature (remember that in the above equation, heat was a byproduct).

A lizard doesn’t have to worry about such things. He’s an ectoderm (coldblooded), so he doesn’t need to maintain the same temperature all the time. Instead he just lets himself cool down or heat up with the outside temperature. Once it’s warm enough, he can get going and catch some food. (The correspondingly low metabolism also helps explain why reptiles can go so long between feedings. A rat, in contrast, has to eat like an elephant to stay alive!)

On the other side of the scale, an elephant, a very large warmblooded mammal, has a much much larger volume than it does surface area. since heat transfer happens only at the surface (the skin), this means the elephant can maintain its temperature rather easily and doesn’t need to worry too much about losing heat. This is great if you’re a mastodon in the snow. However, cooling off in a hot temperature environment becomes a huge pain when you’re huge. As a point of interest, most desert animals are lanky to decrease their volume and increase their surface area. In contrast, cold weather creatures are often more “rounded out” to decrease surface area and increase volume, thereby decreasing heat-loss.

If we think of it that way, a warm-blooded, huge bodied dinosaur in a super hot environment makes little sense. From much of the morphological evidence, many dinosaurs appeared to be quite active. We know they were big. But, if they were big and active, that is they would be increasing their metabolic rate during activity (thereby heat) even higher than baseline we have a problem for an endoderm! Especially if they didn’t have a turbinate bone to decrease water loss!

It is more likely that dinosaurs were cold-blooded (or at least not warmblooded; there is some speculation about gray areas in these matters). A cold blooded animal in a hot environment can be quite active. And they don’t run the serious risk of overheating the way that warmblooded creatures do. Tuna are a good example.

The last thing is a side issue about oxygen levels. Oxygen levels were quite low during the period of time that the dinosaurs rose to power. But, there is mounting evidence that dinosaurs (at least the saurischians) had a specialized kind of air-sac lung system, the same kind that modern birds have (who likely evolved from this subset of dinosaur). This type of lung is FAR more efficient than the one hanging out in your chest (or any chest of a mammal). It’s why birds can fly at altitute and still be so active (they’re flying for heaven sakes!), and we need oxygen masks.

A coldblooded dinosaur with an air-sac lung could have thrived in an environment that was hot and oxygen poor.

FOLLOW UP:

The debate on this topic is far from over.  I tend to side with the idea that Saurischian Dinosaurs were ectotherms, but there are plenty of arguments to throw around.

For more on the topic, here’s a site at Berkeley about it.

And the top five hypothesis:

  1. Dinosaurs were complete endotherms, just like birds, their descendants.
  2. Some or all dinosaurs had some intermediate type of physiology between endothermy and ectothermy.
  3. We know too little about dinosaurs to hazard a guess at what their physiology was like.
  4. Dinosaurs were mostly inertial homeotherms; they were ectothermic but maintained a constant body temperature by growing large. Small dinosaurs were typical ectotherms, maybe with a slightly elevated metabolic rate.
  5. All dinosaurs were simple ectotherms, enjoying the warm Mesozoic climate. But that’s okay; many ectotherms are quite active, so dinosaurs could be active, too.

I’m diggin’ on number 4, with a nod to number 5.

Slime-Bag Dinosaur: What Science Is, What It Isn’t

Carl Zimmer discusses his new piece in Science.  It’s about the 2005 discovery of potential blood vessels from none other than T-Rex.  The trouble is that now there are a few scientists who aren’t all that convinced, instead saying that the vessels are in fact just a bunch of bacterial goo!

That’s all fine and dandy, but what I liked was this comment by one of the original authors, Mary Schweitzer

Something that is not fully appreciated by the outsider is that science is a process. One makes an observation, forms a testable hypothesis about the observation, gathers data, and the data either support or refute the hypothesis. It is then refined and retested. If the hypothesis is tested multiple times, it is strengthened, and eventually moves to become a theory, one of the strongest statements in science.

If one chooses to challenge a hypothesis and the data put forth by another researcher to support it, one is under the obligation to 1. form a hypothesis that provides an alternative to the first; 2. reinterpret the original data presented in such a way that it __better supports__ the new hypothesis than the original, and 3. produce new data that, in addition to the original, more strongly supports the alternative hypothesis than the original. That is the progression of science. Hypotheses are continually being reformulated in this way, because science IS a process, and undergoes revision as new data become available.

A good friend of mine recently complained to me that he didn’t bother reading science information (in the popular media) because it’s “always changing”.  There is a common perception about this,  particularly in medical and health sciences (of which he was speaking directly).  One day we’re not supposed to eat eggs, the next we are.  We should be able to talk while doing cardio, the next it’s interval training.

But, the hard truth is that the popular science media grossly distorts the reality of what actually happens in science, and how exactly people come to decide that eating eggs actually isn’t bad for you.  Science is slow, tedious, and sometimes downright boring.  One new study that looks promising and exciting (and therefor gets tons of media attention) doesn’t mean jack shit.  It has to be repeated, over and over, and shown to be consistently true.

This happened with eggs.  At first a number of studies noticed that eggs had a lot of fat and cholesterol.  Bad.  So the media flips out!  Never eat eggs.  Ever.  The heavens above will rain lava upon you!

But, over the years, study after study has clarified that the composition of the cholesterol and fat in eggs is such that it evens itself out, with a slight nod towards being good for you.  In fact most people who don’t already have high cholesterol would be wise to eat them.  The quality of protein in eggs is ridiculously high, they are packed with nutrients, and they’re relatively cheap.  In addition, there are many brands that are filled with omega-3’s.  Heavens be damned.

Fossil hunting suffers the same fate in the media.  One new fossil can be exciting, “we’ve discovered the missing link” (whatever THAT is).  But, that one fossil doesn’t tell a whole story.  It rarely can give us more than peeked interest to further investigate, or fill in a small gap that leads to another gap.  Multiple fossils, corroborating data from other fields, etc is needed before any conclusions can be reached.

This is going on in science all the time, of course, but you’d have to read the professional journals to know it.  Since most people don’t (hard to blame them, the writing is grotesquely dry), they must rely on the popular media to filter the information.  That wouldn’t be so bad if the media did a good job, reporting regularly on those scientific answers that have the most abundance of backing.  But, they don’t.  They do the opposite!

The media constantly goes after what’s new and exciting, the opposite of what makes science tick.  New is interesting, but tried and true is … well, true … usually.

Solution?  There likely isn’t an easy one.  But, for all my bashing of media science writing, there are a number of very good science writers who try hard to put things in perspective (Carl Zimmer among them).  You just have look for them and be your own filter.