Average Animal Size vs Time

No. They were similar in size to today. They were far larger before the evolution of the dinosaurs.

Is there any reason to think it hasn't? We're talking about animals here, also. Average size fluctuates over extinction boundaries.

That is ontogeny, not descent with modification.

 

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GeoffP has anticipated my responses. I would add on the 'microscopic' question, we have found baterial fossils and as far as I am aware there is no sdiscernible size difference. You may recall that one of the interesting things about the possible fossils found in the Martian meteorite was that they were much smaller than comparable Earth finds.

 

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Bacteria aren't animals- not even close. They don't even make anyone ponder "huh, what is an animal, anyway?" They're very clearly their own clade, and have been that way for a very long time.

Protozoa are a little more animal like (though not really- they lack the organizing Hox homologs that animals have), and fossils from the early Cambrian suggest that some Foraminifera (amoebas in calcium carbonate tests) reached 15 cm in size, as opposed to the largest of protozoa now, which are about 9 mm.

As for size changing over time, I'd think it would have to do with how big continents were. Subdivision leads to smaller habitable area, especially in the case of North-South continents, since there's further subdivision by latitude.

 

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I wasn't clear in my post. I was seeking to demonstrate that if we can detect fossil bacteria in archean rocks and even smaller putative bacteria in meteorites, then identifying microscopic animals would not be an issue. Having re-read what I wrote again, I have no idea how I expected anyone to extract that meaning from my words.

 

I've been told an animal is any member of animalia.

 

So you would agree then that the average size of insects plotted over time would be a bell curve?

 

Insects were large during the times of high oxygen, but dinosaurs were fucking titanic during times of oxygen concentrations half that of today!

 

I don't know why you're so caught up with oxygen levels. Yes, they explain body sizes for organisms whose respiratory systems operate (largely) by passive diffusion. But with a well developed, pressurized vascular system, it's not nearly as important.

 

Well if your asking why insect were large in the past now you have your answer.

 

Are dinosaurs insects?

 

dinosaurs (probably) had unidirectional air-sac lungs the most efficient from to respiration to have evolved, and of course oxygen-carrying blood, insects have nothing but air pores.

 

Average size of an evolutionary lineage will usually increase with evolutionary time simply because the most likely original being in any given new line is small.

On top of the other considerations.

 

Anyone here believe gravity had something to do with the size of dinosaurs?

Because if gravity was the same then as it is now, dinosaurs would not be able to operate efficiently, especially the predators. They would be simply to big to move faster than a few miles per hour, especially the T-Rex, who needed to move fast to catch preys.

If we accept the Earth Expansion theory, and accept that earth was 1/4 the size of earth now (in the time of the dinosaurs), gravity would have been 1/4 of what it is now also. Which means dinosaurs would be able to operate like animals presently. Dinosaurs grew big because the environment allowed them to grow big, and gravity played an important role.

 

you got a reference on that?

 

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The size of animals has decreased over time because, since the Earth is growing, there is no gravitational constant (G).

See Hurrel, S.: http://www.dinox.org/

Attempts to find and solve for G have been an utter failure, which is to say it's a myth.

Gillies, G.T., et al., The Newtonian gravitational constant: recent measurements and related studies, Reports on Progress in Physics, Volume 60, Pages 151-225, 1997

Gundlach, J,.H., and Merkowitz, S.M., Measurement of Newton's Constant Using a Torsion Balance with Angular Acceleration Feedback, General Relativity and Quantum Cosmology, 2000

"It is important to note that all the periods [Earth's orbit and year] were likely of different duration in the geological past." -- Mazumder and Arima, 2004

"This implies that slow Earth expansion might have occured if G varies (Runcorn 1964, pg. 825)." -- Mazumder and Arima, 2004

Muzumder, R., and Arima, M., Tidal Rhythmites and their Implications, Earth Science Reviews, 69, Pages 79-95, 2004

Fixler, J.B., et al., Atom Interferometer Measurement of the Newtonian Constant of Gravity, Science, Volume 315, Number 5808, Pages 74-77, 2007

 

Man Oil, you got the researching part down.

 

Thank you. I wish the opposition did. It would make things more interesting.

 

Don't tease him Scyents

 

We have no idea of the average animal size of past era's. I guess we can make a pretty accurate estimation of todays though.