Sauropod Vertebra Picture of the Week

I was contacted recently by David Goldenberg (dgoldenberg@gmail.com), a journalist who’s putting together a piece on the biggest dinosaurs. He asked me a few questions, and since I’d taken the time to write answers I thought I may as well post them here.

1) Do you think that we will ever know what the largest dinosaur (by mass) was?

In principle, we can never know that we’ve found the largest dinosaur. All we can know (and we probably can’t really know even this, as we’ll see below) is that we’ve found the largest so far. If we were dealing with animals where there’s a good sample size, there would be statistical techniques that we could use to figure out the likely size-range. But most giant dinosaur species are known only a handful of specimens — sometimes only a single one. How big did Puertasaurus get? We can’t possibly say: the best we can do is estimate how big the one known specimen of Puertasaurus was.

That said, we can sort of get a feel for size classes. There are quite a few sauropods that seem to come in at around 30-40 tonnes — Brachiosaurus, Giraffatitan, Supersaurus, Dreadnoughtus — which suggests there might be some kind of a limit there. But there are bigger titanosaurs (Argentinosaurus, Puertasaurus, Futalognkosaurus) which show that if the barrier exists at all, it’s a “soft” one. And of course the tantalising hints of super-giant sauropods.

There are at least three of these: Amphicoelias fragillimus, a diplodocid known from a drawing of a vertebral arch which has since been lost or destroyed, which could well have massed 100 tonnes. Bruhathkayosaurus, a giant titanosaur known from a two-meter tibia, since destroyed, which could conceivably have massed twice that; and the Broome Sandstone track-maker, known only from footprints, which might have been somewhere in between.

Any one of those, we might write off and say it’s too good to be true — all three stories are pretty vague as to evidence and require a lot of guesswork in the inferences. But the fact that we have all three of these makes me feel pretty certain that there were indeed sauropods out there in the 100-200 tonne range (i.e. the size of big whales). I only hope we find solid, verifiable, curated evidence for them some time soon.

2) What bones do you need to have before you can make an accurate measurement?

You can’t ever make an accurate measurement. Consider even a really well represented, essentially complete specimen such as MB.R.2181 (previously known as HM S II), the giant mounted skeleton in the Museum für Naturkunde Berlin. Peer-reviewed published estimates of the mass of that one individual have varied between 13,618 and 78,258 kg — a factor of 5.75. Even if you discard these obvious outlier estimates, recent and credible estimates vary from 23,337 to 38,000 kg, which is still a factor of 1.63.

And this is not completely crazy. Two humans with essentially identical skeletons can weigh 70 and 114 kg, after all. Soft tissue is essentially impossible to predict.

3) What do you make of the fact that so many different species have been given the title? Is that the fault of the media or scientists or what?

A big part of is that it depends on what you count. That Berlin brachiosaur is the biggest dinosaur known from an essentially complete skeleton, so Giraffatitan is a legitimate holder of the crown. (Confusing matters further, it used to be thought to be a species of Brachiosaurus). But there were definitely bigger sauropods than that — just not known from such complete specimens. Argentinosaurus was certainly bigger, for example. But there’s no way to put a meaningful whole-body mass estimate on it.

But yes, there is also an understandable tendency towards sensationalism, both from scientists and the press. There have been plenty of new discoveries that can legitimately be described as “could be the biggest yet”.