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 You are here: Social Behaviour > Foraging > Sauropodomorpha
 
Sauropodomorpha
Ornithischia
      Stegosauria
      Ankylosauria
      Pachycephalosauria
      Ceratopsia
      Ornithopoda

Saurischia
      Sauropodomorpha
      Theropoda

As evident from their size, it is likely that sauropodomorphs fed from the crowns of trees. Unlike other herbivorous dinosaurs (most of which are Ornithischians), the sauropods had much less developed skulls; relatively small and light, with little room for jaw muscles, as well as simple crowns; triangular, spatulate, or slender and pencil-like despite some having ventrally offset jaw joint in sauropods such as Plateosaurus, Coloradisaurus, Apatosaurus, and even Camarasaurus.

P.M. Barrett and G.R. Upchurch have studied in great detail the evolutionary pattern of sauropod feeding by linking various aspects of jaw mechanics and body form with phylogeny. They observed that sauropods lengthened their forelimbs over the primitive condition seen in prosauropods and other saurischians. Not far from the base of the sauropod evolutionary tree is an increase in body size and the development of spatulate teeth, the latter viewed as a means for cropping coarser vegetation.

By the time we reach more derived sauropods, the snout broadens, the lower jaw strengthens, and wear indicating front and rearward movement of the jaws is found on the teeth. Several major changes in the jaw system can be identified with further sauropod evolution. Among neosauropods (which include camarasaurs, brachiosaurs and titanosauroids), and diplodocoids on the other, the skull shows additional strengthening (closure of the antorbital fenestra). Camarasauromorphs generally show a shortening and elevation of the skull, indicating a more powerful biting force, but otherwise retain the feeding features seen in other, more primitive neosauropods. In contrast, the peg-like teeth arranged at the front of the jaws (forming a tooth comb), apical tooth wear (instead of longitudinal), and elongation of the snout in diplodocoids indicate an abandoning of fore-aft jaw movement and a shift to exploitation of a more delicate food source in these animals.

In sum, sauropods evolved a variety of ways to grab onto, and begin to prepare, food in the mouth. Tooth form and especially tooth wear indicate that these gigantic herbivores either nipped and stripped foliage, unceremoniously delivering a succulent bolus to the gullet without much modification in the mouth. It is doubtful that many of these animals fed selectively, given the size of the jaws, the nature of the dentition, and body size, although diplodocoids may have been relatively more selectively than other sauropods.

Swallowing sped the bolus down its long travel along the esophageal canal, whereupon it entered the abdomen, and in particular the gizzard. This muscular chamber, sitting just ahead of the glandular part of the stomach, is thought to have been developed in both prosauropods and sauropods; enclosed within it would have been a collection of gastroliths, rather large and smoothly polished stones that acted as a gastric mill. Conteaction of the walls of the gizzard churned the gastroliths, thereby aiding in the mechanical breakdown of food as it passes further along in the gut.. Gastroliths are known – albeit rarely – in both prosauropods and sauropods (including the discovery of in-place gastropods with the skeleton of Seismosaurus).

In all sauropodomorhs, the gut must have been capacious, even considering the forward projecting pubis (in contrast to all ornithischians, which rotated the pubis rearward to accommodate an enlarged gut). J.O. Farlow envisioned these animals as having an exceptionally large fermentation chamber in the hindgut that would have housed endosymbionts, which would have chemically broken down the cell walls of the plant food, thereby liberating their nutritious contents. Considering the size of the abdominal cavity in sauropodomorphs, these animals probably fed on low-quality food items; perhaps they also had low rates of passage of food through the gut in order to ensure a high level of nutrient extraction from such low-quality food. Still, these huge animals with their comparatively small mouths must have been constant feeders to acquire enough nutrition to maintain themselves. The digestive tract of a sauropods had to have been a non-stop - if slow-speed –conveyor belt.

Being the tallest browsers for the their time - and for all time in many cases - Prosauropods like Euskelosaurus and Plateosaurus were able to feed at up to 3m above the ground, particularly if they assumed a tripodal posture. This was tall for the Late Triassic and Early Jurassic. Likewise, some later sauropods may have been able to do so as well, at least until they felt faint. And the elongate necks seen in all members of Sauropodomorpha certainly extended vertical feeding ranges. Such ranges have been estimated to have been up to four or five stories. In sauropodomorphs capable of rearing up on their hindlimbs to feed, it is likely that the hand manipulated leaves and branches to the mouth or possibly assisted in balancing while the animal craned for foliage just out of reach.

From their anatomy, we have good reason to suspect that sauropodomorphs browsed at high levels. After all, the Late Triassic had plenty of gigantic fern, conifers, cycads and ginkgoes for the likes of Plateosaurus and Massospondylus to feed on, while Jurassic consisted of great variety of conifers, as well as limited ginkgoes, cycads, ferns as well as horsetails for Omeisaurus, Diplodocus and Seismosaurus. And for the Cretaceous sauropodomorphs such as Saltasaurus, Quesitosaurus and Alamosaurus, there were the emergent angiosperms, some of which probably reached tall-tree height before the end of the period.

However, beyond recognizing this potential link between sauropodomorphs and their fodder, we have very little direct evidence of their diets. It has been suggested that a pile of carbonaceous material, old stems, bits of leaves and other plant material collected from the abdominal region of a sauropod skeleton found in the Morrison Formation of Wyoming consituties fossilized gut contents. Interestingly, this skeleton also had a packet of gastroliths in its belly region. Another potential example comes to us from the Upper Jurassic of Utah. Consisting of sections of small twigs and branches, it contains neither leaves nor carbonized residues. If either of these collections of plant hash are to be believed as stomach contents, they give the impression that sauropod digesta was rather coarse and fibrous.

 

References;
Fastovsky, D.E. & Weishampel, D.B (2005) The Evolution and Extinction of the Dinosaurs(2nd Ed.), Cambridge University Press: Cambridge, UK.

 

 
 

 
 
     
© 2008 Earth Sciences, University of Bristol