Geoscience Reference
In-Depth Information
lection must have favored theropods with the visual acuity to pick out the right
rocks(onesthatwererichinsilica)andthementalabilitytothink“Musteatrocks,”
as those rocks would then help them with digestion and overall good health.
The gastrolith connection between non-avian feathered theropods with gastro-
liths in early birds was bolstered by the discovery of gastroliths in the Early Creta-
ceous bird
Yanornis martini
of China. These gastroliths, mostly composed of sand-
and gravel-sized quartz particles, were in exactly the same place where the bird's
gizzard should have been. Another insight provided by this avian rock collection
washowanabsenceofgastrolithsinotherspecimensof
Y. martini
,butthepresence
of fish remains in one, implied that this species might have been switching its diet
seasonally. Some modern shorebirds do the same, eating seeds and insects in the
spring through fall, but chowing down on seafood during the winter. So this Early
Cretaceous bird may have died before the winter while its gizzard was still full of
gastroliths, which it would have needed to fully digest and process fibrous seeds
and insects.
Other theropods with gastroliths include a few species of ornithomimids. In
1890,nearlyahundredyearsbeforethetheropod-birdconnectionwasfirmlyestab-
lished,O.C.Marshnamedonedinosaur
Ornithomimus velox
;bonesofanotherspe-
cies,
O. edmontonicus
, are the most common Late Cretaceous theropods in North
America, and Asian ornithomimids are not exactly rare either. Because “ornitho-
mimid” means “ostrich mimic,” it seems only appropriate now that some of these
dinosaurs, like modern ostriches, also had gastroliths. Ornithomimids with gast-
roliths include the Early Cretaceous
Sinornithomimus
, the Late Cretaceous
Shen-
zhousaurus
, and a dozen specimens of an unnamed species, all from China. The
mostrecent,andoneofthemostexcitingexamplesofgastrolithsinanornithomim-
id, was reported in 2013. More than a thousand rocks, all relatively small, were in
a skeleton of the Late Cretaceous
Deinocheirus mirificus
of Mongolia. The hun-
dreds of gastroliths from the dozen unidentified ornithomimids ranged from sand-
to gravel-sized and were angular to rounded, affirming how gastroliths are the most
