Walking With Dinosaurs, the 1999 documentary, featured herds of Diplodocus with their heads held basically parallel to the ground, reflecting some paleontologists' supposition that for the beasts to raise them much higher would have been an unbearable strain, requiring blood pressure too high for their hearts to bear. The SV-POW! team has weighed in with a strong argument to the contrary, based on the evidence provided by living animals - a fantastic summary is available here. Rather than a straight horizontal line, they argue that it made more sense for sauropods like Diplodocus and Apatosaurus to hold their heads at a gentle curve, with the heads well above their bodies.
Examining the Chinese early Cretaceous sauropod Euhelopus, Andreas Christian from the University of Flensberg has concluded that it was especially adapted for high browsing, a conclusion that likely bears true for similar sauropods, notably the ever-popular Brachiosaurus.
Euhelopus, via wikimedia commons.
As you can see in the above reconstruction, Euhelopus is similar to Brachiosaurus in its marked differences from the standard-issue, Flintstones-style "brontosaur." The front legs are longer than the back, and the tail is shorter. In all, the profile is more giraffe-like. Christian's paper suggests that this posture, while requiring considerable effort to pump blood up through the neck, was less expensive than grazing over a broader area - holding its head at a 90 degree angle from the horizontal for five minutes required only about half of the energy expenditure as walking a hundred meters. He also found that the stresses on the neck vertebra were lower in as Euhelopus held its neck more erect. Christian concludes that "raising the neck... may have been less expensive for a sauropod like Euhelopus or Brachiosaurus than walking a long distance. During a food shortage, raising the neck was probably even essential for surviving: it is better to get little than nothing at all." Not an earth-shattering discovery, but one that adds to our understanding of how such a magnificent adaptation made sense for these animals.
