Geoscience Reference
In-Depth Information
were adhered to plant roots; mineral supplements, such as for calcium or trace ele-
ments; or used as separators for keeping fibrous food from bunching in their stom-
achs.
Nonetheless, the disproving of one explanation for gastroliths in sauropods
doesn'tmeantheysuddenlyvanished.Forexample,onespecimenoftheLateJuras-
sic sauropod
Diplodocus hallorum
(formerly named “
Seismosaurus hallorum
”) of
northern New Mexico had more than 200 gastroliths, which were carefully mapped
inside and around its former body cavity. These gastroliths were all igneous and
metamorphic rocks with varying degrees of polish to them, and most were about 2
to 8 cm (<1-3 in) wide. An assemblage of 115 gastroliths, totaling about 7 kg (15.4
lbs), was also packed into a small area within a skeleton of the Early Cretaceous
sauropod
Cedarosaurus
from Utah. Other sauropods with gastroliths directly asso-
ciatedwiththeirbonesinclude:
Apatosaurus
,
Barosaurus
,and
Camarasaurus
ofthe
western U.S., as well as
Dinheirosaurus
of Portugal (all Late Jurassic sauropods),
and the Early Cretaceous
Rebbachisaurus
from Morocco. In one instance, 14 gast-
roliths were directly associated with the remains of a juvenile
Camarasaurus
scav-
engedby
Allosaurus
,thelatterindicatedbytracks,toothmarks,anddislodgedteeth.
Several specimens of a Late Triassic prosauropod from South Africa,
Massospon-
dylus
—the same dinosaur affiliated with nests, eggs, and babies mentioned in a
previous chapter—had gastroliths too. Moreover, the skeleton of another prosauro-
pod, the Early Jurassic
Ammosaurus
of North America, had gastroliths. In short, al-
though gastroliths are relatively rare, having been found in less than 4% of all saur-
opodskeletons,thesetracefossilsareabundantenoughinthemthattheyshouldnot
be ignored, either.
Soimagineyouarea20-tonsauropodandwalkingalongastreambankduring
the Late Jurassic. At some point during your stroll, you get a serious hankering for
some geo-gastroliths, and you don't know why, because your brain is smaller than
that of a 0.075-ton (150 lbs) human. How do you pick the right rocks? The cerebral
processingneededtodiscriminatebetween“good”rocks(solidsilica-richones)and
