THE FACE OF DIPLODOCUS: Nostril Placement in Sauropod Dinosaurs

In writing and illustrating our 2016 Johns Hopkins University Press book, The Sauropod Dinosaurs: Life in the Age of Giants, my coauthor Matthew J. Wedel and I sought to explain the most current ideas about the paleobiology and ecology of this enigmatic dinosaur group.

- Mark Hallett 2020

Besides the often contested issue of how sauropods held their necks and whether they could bipedally or tripodally reach high to browse, one topic we touched on was breathing. Here we discuss not the remarkable system of oxygen and carbon dioxide exchange in the sauropods’ birdlike unidirectional lungs, but the simple aspiration of air and the basic question of where the fleshy external nostrils (external nares) were placed on their heads. This obviously makes a huge difference in the appearance of the animals, and also has a direct relationship to a basic problem for sauropods when they became really huge: how to keep breathing while you have to drink.

At this time we still don’t know how whether sauropods, as with some extant giant mammals such as elephants, were heavily dependent on liquid water or, like some species of mammalian herbivores such as macropodid kangaroos, could obtain whatever water they needed from the plants they browsed. Because sauropods didn’t chew their plant food like other dinosaurian herbivores (Hallett, Wedel 2016), they would have to have been dependent on massive amounts of saliva to help the esophagus’ (food tube’s) muscular contractions sluice the fibrous material down their long throats. To create this a lot of moisture was constantly needed, probably to some degree in the form of free water from ponds, rivers or lakes. For sauropod species like Camarasaurus, Barosaurus, Diplodocus, Brachiosaurus and others that lived in seasonally arid environments like the Late Jurassic western US, an efficient system of water retention from browse would certainly have been adaptive, but the huge creatures may have also habitually migrated to local or more long-distance free water sources if these were available.