How do you make a really big dinosaur?

Euhelopus, showing the elevated neck posture. Art by DiBgd, image from Wikipedia.

Euhelopus, showing the elevated neck posture. Art by DiBgd, image from Wikipedia.

To me, one of the best ways to read about science isn’t to read about what they know, but to read about what they’re trying to figure out.

We all grew up with pictures like this — unbelievably huge dinosaurs with impossibly long necks. For a kid, a big part of the attractiveness of dinosaurs is their sheer bigness. Not all dinosaurs were large, of course, but from a kid’s perspective, the bigger and weirder the better.

One thing I never considered is how the biology actually works at that size. There’s a problem of scale. If you’re trying to pump blood from a heart up the fifty-foot neck of a Supersaurus, wouldn’t you have to have a massive heart, incredibly high blood pressure, or maybe some sort of auxiliary pumping mechanism to make it work?

Turns out, paleontologists have a lot to say about this. It’s a mystery they haven’t quite unraveled yet. A few months ago Brian Switek posted a fascinating article about this at his “Laelaps” blog at National Geographic. I’ve been meaning to post about it ever since.

Switek writes of a team of scientists who argued that sauropods must have kept their necks low:

After calculating the pressure that a sauropod such as the approximately 80-foot-long Barosaurus would have required for blood to reach the dinosaur’s head (estimated at 700mmHg), Seymour and Lillywhite wrote that the left ventricle of the dinosaur’s heart alone would have weighed two tons, or about fifteen times heavier than the left ventricle of an equally-long fin whale. And even if such an enormous heart existed, the researchers reasoned, the organ would have been grossly inefficient. Such a monstrous heart seemed unlikely.

Other scientists argue that sauropod bone structure indicates that some species that kept their heads elevated — some as much as twenty-six feet above their hearts. So that points toward big hearts and exceptionally high blood pressure, but the anatomy is speculative at this point. What’s more, we don’t know how these huge creatures kept blood from pooling in their extremities or how they avoided a fatal head rush when lowering their heads — but in this case, looking at present-day animals like giraffes and horses provide some clues of how it could have happened.

In many ways, we’re still only getting to know these giants. Paleontologists are assembling a more refined look at sauropods than has ever been possible before, yet it’s the questions -– the persistent mysteries –- that keeps sending scientists to pore over bone and wonder about long-lost soft tissues.

Yes, that’s it. What gets scientists excited is the knowledge that’s waiting just beyond the frontier of the known.

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