The skull of a titanosaur
has been reconstructed.
The largest animals known to have walked the earth, sauropods were common in North America during the middle of the dinosaur era but were thought to have been pushed to extinction by more specialized plant-eaters at the end of that era. New discoveries, however, are showing that one lineage of sauropods diversified at the end of the dinosaur era, University of Michigan paleontologist Jeffrey Wilson says.
Wilson's recent restudy and reconstruction of the skull of a Mongolian sauropod adds to a growing body of evidence for sauropod diversity at the end of the dinosaur era. Wilson described the reconstruction and the conclusions he drew from it in a paper published Aug. 24 in the Journal of Systematic Palaeontology.
The reconstruction is important for several reasons:
"Most animals walk with a narrow gauge, with their feet close to the midline, because it's energetically more efficient to walk that way. But some sauropod trackways tell us that a group of sauropods were walking with a new wide-gauge stance. We can identify characteristics of titanosaurs that would have allowed that stance, and we can tie the appearance of those features with the proliferation of wide gauge tracks everywhere in the fossil record at the end of the dinosaur era." Wilson wonders if the change in locomotion—from typical sauropod narrow-gauge walking to titanosaur wide-gauge walking—corresponded to lifestyle changes, such as different feeding habits. But without skulls to study, it has been hard to draw conclusions about how and what titanosaurs ate.
One feature of the skulls is particularly intriguing. "They have elongate, sort of horse-like skulls with many openings and grooves on the outer surface of their snouts," said Wilson, who worked closely with U-M Museum of Paleontology artist Bonnie Miljour over the course of a year preparing the paper's many illustrations of the skull reconstruction. "Blood vessels and nerves passed through these holes and may suggest an especially sensitive snout. This probably had some role in feeding, but we haven't investigated it at all."
Oddly, a group of distantly related sauropods evolved a similarly grooved snout. "Apparently, these two different branches of sauropods gravitated toward similar anatomical structures, perhaps because they were specialized for eating certain types of vegetation."
Titanosaurs are found in widely scattered locations from Patagonia to Madagascar to Mongolia and have yeilded some interesting insight into dinosaur evolution. For example this find (first picture above) in Madagascar allowed the resolution of an interesting issue:
The discovery of the skull of Rapetosaurus showed Curry Rogers and Forster that two enigmatic sauropods from Mongolia (Nemegtosaurus and Quaesitosaurus) are actually titanosaurs, and not, as theorized, more closely related to other sauropod families. Rapetosaurus was key in this resolution, since it provides both a skull and skeleton for comparing titanosaurs (previously only known from skeletons) to these two Mongolian dinosaurs (known only from skulls).
