Posts Tagged 'mass'

The unconsidered fatness of dinosaurs

I am always interested in ways of measuring or estimating the mass of organisms. While estimates are generally given as a range rather than an exact figure (which makes sense of course) the range is generally there to provide for possible errors in the methodology – were the animals good runners so the legs should have a bit more musculature, was the tail a bit longer, were the neural spines a bit longer? But there is also a further component that is rarely considered (or at least not discussed) – how robust (or lets face it, fat) is the animal?

Now I am not going to criticise estimates for not considering fat tyrannosaurs (though John Hutchinson for example does work with ‘gracile’ and ‘robust’ morphs which accounts for the possible variation present), but those working from them (for e.g. mechanical analyses) should give them a little more thought in my opinion. While it is easy to look at a human population and spot, shall we say, some highly robust morphs, that is a result of excess food being available, not just changes in form or build. While at London Zoo, I worked with a pair of female giraffe where one was probably half a meter taller than the other, but a fraction of the girth – the latter (while a guesstimate) was probably 10% heavier despite a difference in height (measured) of around 7%, with the shorter animal being the heavier. At a more familiar level, while discussing mass estimates in Munich, my fellow pterosaur researcher Mark Witton revealed that he weighs just 65 kg, compared to my then (to my shame, and I desperately point out, after a major sports injury that had prevented any real exercise for months) almost 100 kg, despite the fact that we are near identical heights and similar in build (well, broad shouldered). Even at my more normal ‘fit’ weight of about 85 kg there is clearly a big difference between us despite our similar height (and build actually, at least in terms of shoulder width). Mark is simply far more gracile than me for want of a better term, despite an apparently similar osteology. Either of us would probably be considered well within the normal range of humans, (and perhaps for other animals – i.e. about 20% for a given size) but it is really quite dramatic.

Assuming (i.e. not checking) this is normal, even a near perfect estimate that gave T. rex a mass of say 8 tons, means that for a given skeleton, anything from 6.4 – 9 t might be in the normal, let alone extreme range for the species. That is a big range and can have a considerable effect on wider analyses (such as running speed, ecological biomass etc.). Again, it might be difficult if not impossible to include this realistically into mass estimates (you are looking to get a narrow range after all for practical work, not be left with a hugely unworkable range that encompasses every concievable extreme) but it is worth keeping in mind what kind of variation is possible. Yes our hypothetical 8 ton rex might be a perfect estimate for that specimen when it was alive, but it could have been much bigger or smaller. Perhaps a very gracile form was normal, and rexes of that size rarely got above 6.5 t in which case an analysis of their food requirements for example could be severely affected. If the results come out for some ecological analysis for example suggesting that at an average of 8 t, Tyrannosaurs was badly overpopulated compared to the amount of prey, remember that he might not be quite the giant you think…

This is a revised Mk.1. post, to see the original with comments etc., go here.

How many elephants?

I do so love The Onion – for those who have missed it, it’s a satirical newspaper in the US that also has a very good online section. I spotted this recently (see it here) and while it raises a good chuckle as a concept, it does also highlight a point about science communication (yes, *that* again, or even, yes, that *again*).

I appreciate then when reporting these kinds of things (how big some new dinosaur is, how deep a new cave goes or whatever) it is incredibly useful to give people a frame of reference. Just how tall is 13 m? What does 50 tons look like? These are tricky concepts for people who are not used to dealing with things like that, so relating them to a familiar concept or everyday physical object will really help to get the point across.

However, the problem comes from the non-standard units being used. OK, so in the UK at least buses are pretty much uniform, but we are forever getting weights in elephants and heights in stories and these are hardly standard measures! I am looking out of a 7th storey windown into one that is on the tenth floor of the building opposite. Oh. So a putative dinosaur that could stretch to the 10th floor could be horrifying visitors in the hotel opposite, or I would be staring at the middle of its neck while it savaged (or not) people about 8 or 10 metres above me. Hmmm. And elephants. Adult female Indian elephants weight about half that of big African bulls. So if this dinosaur weighted the same as 30 elepahnts – which? I could double or halve its weight at a stroke….

Now I know this might seem pedantic (how unlike me), but this does seem to undercut the point of the comparison. The idea is to give people a frame of reference, but instead all it does is add ambiguity. Thirty metres is thirty metres whether Joe Public gets it or not, 10 storeys is not an SI unit. Ok, so it is also unreasonable to ask the press to say “weighed as much a 7 adult bull African elephants” instead of “weighed as much a 7 elephants”, as they just won’t do it, but they could at least find a better comparison. The Times is expecially good at this, using buses, football pitches (which while non standard, vary only a little in length / width) or well known buildings and landmarks like Nelson’s column, so it is certainly possible.

It is handy to get people to appreciate some of the numbers that science throws up, not everyone is au fait with light years, millions of years, tons, kph and the rest, either as absolutes or just concepts. Finding a way of expressing that is useful, it makes science more accessible. But it tends to be at the expense of actually communcating the figures in the first place. What’s the point of trying to show the public what ’30 m’ means if you use a highly variable reference point like the height of a house that leaves people with a frame of reference that could be twice the intended number?

This is a revised Mk.1 post, to see the original with comments etc., go here.

Estimating Dinosaur Sizes

One repeating theme of my research is the evolution of gigantism. Not just why or how some animals got to huge sizes but also answering questions about how they functioned. But what concerns me here is estimating the size of an animal based on what is frequently a little more than a few fragmentary remains. It’s something I think is rarely taken into account.

Of couse we first have to establish what we mean by ‘size’. Lets take a fairly obvious example – Brachiosaurus. We can talk about how big he was in 3 main ways – length, height, and weight (mass).

Although Brachiosaurus was a tall animal, no-one really uses height nowadays as a serious measure of overall size. After all, many dinosaurs were long but relativly ‘short’ in comparison to Brachiosaurus, like a typical *Mamenchisaurus*. Allthough height is, of course, it is still usefull for comparing some animals – notably hominids, but also for determining what browsing competitors Brachiosaurus is likely to have. So already we are down to two, but now it all starts to get a bit serious.
Continue reading ‘Estimating Dinosaur Sizes’

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