Dinosaurs were lighter than previously thought, new study shows

Jun 05, 2012

Scientists have developed a new technique to accurately measure the weight and size of dinosaurs and discovered they are not as heavy as previously thought.

University of Manchester used lasers to measure the minimum amount of skin required to wrap around the skeletons of modern-day , including reindeer, , giraffes and .

They discovered that the had almost exactly 21% more than the minimum skeletal 'skin and bone' wrap volume, and applied this to a giant Brachiosaur in Berlin's Museum für Naturkunde.

Previous estimates of this Brachiosaur's weight have varied, with estimates as high as 80 tonnes, but the Manchester team's calculations – published in the journal Biology Letters – reduced that figure to just 23 tonnes. The team says the new technique will apply to all dinosaur weight measurements.

Brachiosaurus scan

Lead author Dr Bill Sellers said: "One of the most important things palaeobiologists need to know about fossilised animals is how much they weighed. This is surprisingly difficult, so we have been testing a new approach. We laser scanned various large mammal skeletons, including polar bear, giraffe and elephant, and calculated the minimum wrapping volume of the main skeletal sections.

"We showed that the actual volume is reliably 21% more than this value, so we then scanned the Berlin Brachiosaur, Giraffatitan brancai, calculating the skin and bone wrapping volume and added 21%. We found that the giant herbivore weighed 23 tonnes, supporting the view that these animals were much lighter than traditionally thought.

Dr Sellers, based in Manchester's Faculty of Life Sciences, explained that body mass was a critical parameter used to constrain biomechanical and physiological traits of organisms.

He said: "Volumetric methods are becoming more common as techniques for estimating the body masses of fossil vertebrates but they are often accused of excessive subjective input when estimating the thickness of missing soft tissue.

"Here, we demonstrate an alternative approach where a minimum convex hull is derived mathematically from the point cloud generated by laser-scanning mounted skeletons. This has the advantage of requiring minimal user intervention and is therefore more objective and far quicker.

"We tested this method on 14 large-bodied mammalian skeletons and demonstrated that it consistently underestimated body mass by 21%. We suggest that this is a robust method of estimating body mass where a mounted skeletal reconstruction is available and demonstrate its usage to predict the body mass of one of the largest, relatively complete sauropod dinosaurs, Giraffatitan brancai, as 23,200 kg.

"The value we got for Giraffatitan is at the low range of previous estimates; although it is still huge, some of the enormous estimates of the past – 80 tonnes in 1962 – are exaggerated. Our method provides a much more accurate measure and shows , while still huge, are not as big as previously thought."

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More information: Images: WI Sellers & PL Manning

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HannesAlfven
1.3 / 5 (16) Jun 05, 2012
There is great motivation to show that dinosaurs were not as heavy as they superficially seem they must have been. We should expect that papers which somehow demonstrate that dinosaurs were lighter than they seem will tend to get published, for it solves this problem.

But, notice that few people seem to ask how it is that the dinosaurs were so large, to begin with, without making any assumptions about what the world was like back then. Our current gravity appears to preclude the sizes we see, and the land-based mammals tend not to exceed elephants today. I've seen press releases here on physorg which seem to indicate that the models have been difficult to work, for some of these beasts, given today's conditions.

What should be happening -- but, which isn't -- is inferences without assumptions. The inferential step should always include a wider consideration of inferences than simply those offered by the scientific framework itself -- or we can expect confirmation bias.
Sonhouse
5 / 5 (7) Jun 05, 2012
Hannes, one thing you may be forgetting is the amount of oxygen in the atmosphere at that time, which was considerably higher than today.
jsdarkdestruction
2.3 / 5 (6) Jun 05, 2012
alright hannes, what do you think? is it based off your electric universe idea(note i didnt say theory or hypothesis)?
Urgelt
5 / 5 (4) Jun 05, 2012
Oxygen has been shown to be very important in setting upper boundaries for animal mass.

There is a case, though, that defies this correlation. Up until about 150 million years ago, insect size and atmospheric O2 concentrations tracked closely. Then the correlation dissolved; insects became smaller despite oxygen trending, which remained high for tens of millions of years.

Just recently, a paper was published to solve this conundrum. Insects began to shrink at the same time birds diversified and acquired modern bird-like traits. At that point, selective pressure for agility became critical in insects.
Shabs42
5 / 5 (5) Jun 05, 2012
measure the minimum amount of skin required to wrap around the skeletons of modern-day mammals


Any reason they didn't use modern-day reptiles?
CardacianNeverid
5 / 5 (4) Jun 06, 2012
That's a great new tool. I wonder whether the correlation holds over all sizes, for example for smaller, lighter animals like cats, mice, etc, or for aquatic animals.
antialias_physorg
5 / 5 (4) Jun 06, 2012
It would be interesting to look at the bone structure and see if we can get a derived weight bearing capacity from that.

The thickness and density of trabeculae within the bone (or whether the overall morphology is platelike or rodlike) is related to how much weigh the bone has to support. We have a lot of data on this from studies of osteoporotic patients.
Especially the point where osteoporotic breaks occur (i.e. where a bone breaks, like the hip or a vertebra, without any external cause in osteoporitc patients) would give us a lower limit to the weight of dinosaurs.

Any reason they didn't use modern-day reptiles?

There are few reptiles that had a similar gait to the large dinsoaurs. Posture determines how your skin stretches, where fat deposits lie, etc.
Origin
2 / 5 (6) Jun 06, 2012
It's possible, the (skeletons of) fossilized animals are systematically more squashed, than those (of) living ones, which leads into underestimation of their weight,
Megapixel
1 / 5 (11) Jun 06, 2012
The Gravity Theory of Mass Extinction (www.dinoextinct.com) explains why many dinosaurs reached gigantic proportions; it was reduced surface gravity. Reduced surface gravity was not the result of an expanding Earth or the accumulation of cosmic debris.

The theory explains how surface gravity approached current levels around 251 Mya and 65 Mya, playing a dominant role in extinctions at those two times, but was much lower during most of the Phanerozoic Eon.
Shelgeyr
2.8 / 5 (9) Jun 06, 2012
Scientists have developed a new technique to accurately measure the weight and size of dinosaurs...


No. No they haven't. "Accurately measure" is the wrong phrase to use here. They've developed a new technique to ESTIMATE the weight and size of dinosaurs - one that strikes me as pretty clever and likely more accurate (if such a thing could ever be determined) than previous methods, but it is NOT a method to "accurately measure" their subject absent having a real example to compare to. Using modern mammals to calibrate may be the best available option, but it is no confirmation of accuracy.

Still, sounds like good work.
HannesAlfven
1.4 / 5 (9) Jun 07, 2012
Re: "alright hannes, what do you think? is it based off your electric universe idea(note i didnt say theory or hypothesis)?"

This is speculative science here. The models will say whatever it is that the researchers want the models to say. There are typically enough fudge factors to convey any intended result. People who work in marketing will tell you just as much.

Uncertainty plays an important role in our culture: Among many other things, it encourages people to keep an open mind for alternatives. It also helps kids to justify an interest in science: If we present science as an assortment of facts, all figured out already, kids will not surprisingly simply move on to an area where they can still make a difference.

There are important ramifications to the widespread practice of overplaying the results of computer simulations. There are risks here which nobody seems to care or talk about.
HannesAlfven
1.4 / 5 (9) Jun 07, 2012
Re: "Hannes, one thing you may be forgetting is the amount of oxygen in the atmosphere at that time, which was considerably higher than today."

If we always settle on the first or most popular explanation which we can conceive, it only serves to make us more collectively ignorant about the alternatives. Any professor with the proper credentials and access to machines and grad students can create a simulation which validates some aspect of conventional wisdom. And it will likely get published.

But, what about this pertains to the process of critical thinking and creative problem-solving? At what point do we ever question the assumptions which go into these models? It seems to me that the answer to this is essentially never. To the extent that alternative scientific frameworks are ignored, we really have no idea what a competing inference should look like.

And so I feel the need to stress to those who want to ridicule the Electric Universe: Please turn your brain back on.
jsdarkdestruction
3 / 5 (6) Jun 09, 2012
"all figured out already,"
bullshit, NO ONE but you and your kind say that. get back into reality and back on the meds bro. you'll find life is more enjoyable without the paranoid delusional thoughts running through your head all the time. your brain may be "on" but it's not operating correctly. my brain is always on, thats why i dont give a word you say any credence, i can see the massive flaws in your typings pretty easy. you are not convincing anyone here so why do you waste your and more importantly our time posting here?
Shakescene21
2.6 / 5 (5) Jun 10, 2012
Very interesting, but I wish they had measured hippos and rhinos in addition to elephants, giraffes, reindeer, and polar bears. In particular, the reindeer and polar bear have a very different habitats and lifestyles from a Brontosaur. It would be especially interesting to learn if a hippo conforms to the 21% rule.
This conclusion that dinosaurs were probably slimmer than we believed is consistent with previous studies which concluded that dinosaurs were probably faster and more nimble than was previously believed.
antialias_physorg
5 / 5 (2) Jun 10, 2012
Very interesting, but I wish they had measured hippos and rhinos in addition to elephants, giraffes, reindeer, and polar bears.

The point was probably to take very disparate animals to show that the 21 percent value holds a wide range of animals - and is not just an arbitrary value fit to some specific subset.
Shabs42
5 / 5 (2) Jun 12, 2012
The point was probably to take very disparate animals to show that the 21 percent value holds a wide range of animals - and is not just an arbitrary value fit to some specific subset.


I still think they should have at least thrown in a crocodile, alligator, or komodo dragon. At least see if reptiles give some wildly different number.
antialias_physorg
5 / 5 (2) Jun 12, 2012
If I were to hazard a guess then the scales (especially with crocodiles and alligators) would throw off the results.

For smallish animals the scales add to the structural stability of the skin and so can increase the suported volume. With largish creatures (like dinosaurs) the skin stretches over the bones in a minimal energy configuration (sort of like a soap skin will stretch over a scaffold). Only exceedingly large scales would detract from that (not that there weren't some dinosaurs that didn't have large scales - if memory of my childhood books on dinosaurs serves)