[spindritf]

So what's their secret? How did they manage to feed themselves? Were they living sparsely? Was bioshpere denser then? Were they capable of eating just about anything?

And how was such massive size selected for? Is it just a matter of warmer climate and a feedback loop with larger and larger predators?

[Dn_Ab]

The short answer for why dinosaurs got so large is because they could. That might seem a flippant answer but they had much less constraints than most animals left living today:

Air sacs not only allowed more efficient breathing but were also within skeletal structure, allowing for light weight strength. They also laid lots of small eggs so less reproductive investment per chick. Small heads on long necks with a sturdy body allowed long range eating without moving. With small heads and no chewing the disadvantages of long necks are well handled. For much more depth I encourage reading:

http://phenomena.nationalgeographic.com/2013/02/25/dinosaur-...

<speculative As a non-expert my own guess would be some kind of food-weight advantage feedback cycle. The larger ones were not just more protected from predation but with longer reach came wider access to edible plant material. However, the larger sauropod size, coupled with no chewing and low grade of food (and probably not stones users) required larger and larger (fermenting?) stomachs to get enough energy to support their size. (not directly related but, reasoning from whales they might have even been cancer resistant. And if you consider that their size strongly suggests a 'cold blooded' like metabolism, then given their size, sauropods could well have lived a couple hundred years) />

[givan]

I don't know what was different before but also humans were bigger http://en.wikipedia.org/wiki/Giant_of_Castelnau

[eponeponepon]

Nothing was different. The "Giant of Castelnau", even if he/she was actually as tall as the discoverer conjectured, wasn't wildly outwith the recorded range of human height - Robert Wadlow was 8'11" (2.72m) when he died, and was only 22. It's completely plausible to me that someone afflicted by the same disorder as Wadlow could've reached 3.5m just by being lucky enough to live longer, and it's also completely plausible to me that it could've happened more than once in the vast, vast swathe of human history about which we know next to nothing.

Scant evidence that a human was once very large certainly isn't evidence that "humans were bigger", and that in turn wouldn't be much evidence that a difference in the environment was causing it.

[learc83]

>It's completely plausible to me that someone afflicted by the same disorder as Wadlow could've reached 3.5m just by being lucky enough to live longer,

That's not plausible at all. Robert Wadlow as at the very limits of human height. He already numerous medical problems caused by his height and needed leg braces just to walk.

There is no way a bronze age man with access to bronze age medical care was able to live long enough to grow nearly 3 feet taller than Wadlow.

Since weight doesn't scale linearly with height, a 12' tall man would be enormous. Robert wadlow weighed nearly 500 pounds. A 12' tall man would weigh much much more than that.

I think there are only 2 real possibilities to explain the giant. Either he wasn't really as tall as the discoverer thought, or something was different to allow him to get that tall.

[daniel-cussen]

I know little about the subject, but I'm sure there are differences between the limits of human height and the limits of biped primate height. If the giant of Castelnau were, as claimed, part of a "race of giants," it is not unreasonable to think this group explored the limits of biped height more profoundly, as a group, given that they could eliminate some (but not all) of the problems that height suggested.

On the latter point:

"There is no way a bronze age man with access to bronze age medical care was able to live long enough to grow nearly 3 feet taller than Wadlow."

You don't know that. Even in antiquity, with Iron Age medical care, men commonly lived to 100 years, with the absolute limit, as placed by the Etruscans, at 110 years, thus defining the Etruscan century at this number. Now, perhaps if the man in question was a giant there would be intrinsic difficulties in being gigantic, but natural selection within his tall genetic group could, as a group, overcome many of them. This is a very different situation that Robert Wadlow's, who did not come from exceptionally tall parents. If a group has selective pressure to become tall, it's an entirely different matter from an individual accidentally becoming tall.

Keep in mind there have been around 60 billion Homo Sapiens Sapiens, most of them outside historical record, and in prehistory, very isolated. This can commonly lead to vast phenotype differences. I would have to see stronger evidence to rule out that an adapted giant biped cannot reach 15 feet.

[learc83]

>I would have to see stronger evidence to rule out that an adapted giant biped cannot reach 15 feet.

I didn't say an adapted biped can't reach 15 feet, but a modern human with a pituitary tumor cannot. Which is what the OP suggested. There are too many health problems associated with 9' giants of Wadlow's type for bronze age medicine to overcome, much less 12' or 15' giants.

>You don't know that. Even in antiquity, with Iron Age medical care, men commonly lived to 100 years, with the absolute limit, as placed by the Etruscans, at 110 years

I'm not talking about the lifespan of a normal human who happens not to develop any terminal illnesses, I'm talking about the lifespan of a giant with a pituitary tumor. At the extremes they have too many medical problems to live anywhere near a normal lifespan. Wadlow could barely walk, he couldn't feel his legs so he constantly developed blisters (this is what eventually killed him by the way), and like all extreme giants he had heart problems because his heart was enlarged and couldn't handle his pumping blood throughout his enormous frame.

Keep in mind these are the problems with a 9' giant. Now imagine the medical problems of a 12' giant. He would be a third taller and probably at least 2 times heavier. There is no way someone like that is going to survive in the bronze age, unless he is either of a subspecies that is adapted to growing that tall, or conditions were somehow different.

[eponeponepon]

> At the extremes they have too many medical problems to live anywhere near a normal lifespan.

Absolutely, yes - and, given that the normal lifespan has been three score and ten for about as far back as we can see, and given that Wadlow managed only one score and two, what're the odds that nobody with Wadlow's afflictions ever managed longer?

My point is, Wadlow's death was effectively a matter of poor luck - a blister popped up and went septic that he didn't notice soon enough, but others had previously been spotted and dealt with. Who's to say that no Iron Age 20 year old could possibly do better?

[mcv]

> "Even in antiquity, with Iron Age medical care, men commonly lived to 100 years,"

But that's not remotely comparable to someone growing 3.5 meters tall. Nowadays there are also plenty of people who live more than 100 years, and not all of them need extensive medical care.

Growing to 3.5 m is more comparable to finding someone who lived to 200 years.

[mcv]

"There were giants in the Earth in those days..."

I don't mean to suggest credibility for the antediluvian weirdness in Genesis, or Greek stories about titans for that matter, but this kind of stuff certainly makes you think.

[guelo]

That was not before, that was now. Those human bones are 10,000 years old while the dinosaur bones are 100 million years old.

[noselasd]

No. One man was big. Or it might have been a fraud.