> Hello Aine, There is a fair deal of evidence to
> suggest that catastrophism may be the norm rather
> than uniformitarianism on the planet. Immanuel
> Velikovsky and others have suggested this.
> Megafauna and dinosaurs may have thrived because
> of different atmospheric conditions that may have
> occurred rapidly over and over in the past.
> Evidence points to Native Americans in this
> country being the ones who are claimed to have had
> very large rulers. Although there are many Native
> traditions of an ancient enemy that was portrayed
> as Giant, malevolent and Caucasian, physical
> evidence is scant. Is it possible that royal
> bloodlines were kept in place and eventually died
> out? This is what many Native people would say.
> Comparative mythology paints a different picture
> of the past that includes Giants, Little people,
> ancient floods and cataclysms and an advanced
> ancient civilization. We investigate these ideas
> and I must say that Graham's new book Magicians of
> the Gods makes a very sane and reasonable case for
> some of these notions having a basis in reality.
> W. J. Holland was a paleo-anthropologist and head
> of the prehistoric anthropology department for the
> Carnegie at the turn of the century, he reported
> unearthing an 8 to 9 foot skeleton at the Mckees
> Rocks mound site I believe in the 1890's. I would
> like to see if Holland made any specific
> measurements or took photos. Thanks for the reply
I don't mind Catastrophism at all...but not Velikovsky. Let's leave him out of it, shall we?
You're asking the wrong question. The question isn't how atmospheric conditions affect size...it's how it affects metabolism. Modern atmospheric conditions could support animals as large as dinosaurs. It already supports very large plant life even in a CO2 starved world. I assume you're talking about oxygen. Oxygen didn't drive size although it would have made it easier to get big if you're warm blooded AND develop an efficient O2 transport system. (The addition of O2 to the atmosphere via cyanobacteria led to the first Great Dying, but also allowed for multi-cellular organisms and greater energy available to become mobile.) Warm blooded animals must expend a great deal of energy to stay warm, and to do that must consume a lot of O2 and have efficient O2 transport. Large warm blooded animals need even more, so it may be that being warm-blooded outweighed the advantage of size.
Most dinosaurs were small, and even the modern elephant would give dinosaurs a run for their money in the size department. Dinosaurs appeared in the Triassic, when O2 was at 16% (less than today). Atmospheric O2 levels have been relatively stable for 600 million years. The blue whale is the 2nd largest animal to EVER live on Earth, and it does it at modern O2 levels. The average blue whale is growing, by the way, thanks to an abundant food supply.
Take people who live at altitude as an example. There's simply not enough O2 to feed cells, tissues and organs. The ribs and chest enlarge to accommodate the increase in lung size and hemoglobin is unsaturated. The effects on people not acclimated to it can be deadly as climbers know all too well. Above a certain level, women can't carry babies to full term.
More abundant O2 would have helped critters with more inefficient O2 transport mechanisms...such as insects, which are cold blooded and don't need as much O2 because they don't expend as much energy. Competition for resources drove size. For example, a dinosaur that could reach high leaves had an advantage over those that couldn't. It's obviously easier to defend yourself against predators if you're bigger.
You can see this in your plants if you have a garden. For every plant, especially those close together, it's a contest for adequate sunlight in order to photosynthesize. So they all try to outdo each other by growing taller. Try it at home and you'll see. Competition drives size. See also lignin.
Unless you're not talking about oxygen.
Edit: The McKees Rocks mound site? I know where that is. People are still trying to get the bones returned for reburial there. There's a group that wants to create a park out of the mound. No mention of a 9 footer than I can find, though.
Edited 2 time(s). Last edit at 13-Nov-15 18:00 by Aine.