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• Theirproportions,suchasratiosoflengthsandwidths,werealmostidentic-
al to those of gastroliths described from the Early Cretaceous sauropod
Cedarosaurus .
• Nearly all were rounded, with few angular corners.
• All had some degree of polish to them, and over their entire surfaces.
• Their colors ranged from dark yellow to yellow-orange to brown to dark
red.
• Their surfaces had plenty of pits and gashes in between polished surfaces,
details revealed through a closer look with an SEM.
Do any of these traits sound familiar? Yes, they should. The paleontologists
further concluded that the gastroliths were likely used as gastric mills, helping to
mix and wear down food in gizzard-like organs. So these stones were good can-
didates as dinosaur gastroliths. Still, the paleontologists had a few more questions:
Which dinosaurs carried these rocks in their bellies, where did they get them, and
how far did they travel from their source area?
The answer to the first question was simple: prosauropods. This was based on
the size of the gastroliths—the largest of which could only have been in relatively
big animals—and their resemblance to gastroliths in the sauropod Cedarosaurus .
However, sauropods were rare in the Late Triassic and did not become more wide-
spread until the Middle Jurassic Period. So the closest ecological analog to these in
the Late Triassic would have been the largest herbivores at that time, which were
prosauropods. Furthermore, the size range of the gastroliths (2-5 cm wide) com-
pares well to that of gastroliths in the Early Jurassic prosauropod Massospondylus .
Unfortunately,thebodyfossilrecordforLateTriassicprosauropodsinNorthAmer-
ica is quite scanty, with no bones or teeth known from the eastern U.S., and only
a few prosauropod tracks. These trackmakers might have been the same gastrolith-
bearing dinosaurs that lived in the area of the present-day Bull Run Formation, or
at least been related to them. But with so little other evidence for prosauropods, to
say anything more would require some great speculative leaps. Nevertheless, these
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