Gallimimus
Name:
Gallimimus
(Chicken mimic).
Phonetic: Gal-lee-mime-us.
Named By: Halszka Osm�lska, Ewa Roniewics
& Rinchen Barsbold - 1972.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Ornithomimidae.
Species: G. bullatus (type).
Diet: Uncertain but possible omnivore.
Size: Holotype individual about 6 meters long.
Isolated fossils suggest that some individuals may have grown larger.
Known locations: Mongolia - Nemegt Formation.
Time period: Maastrichtian of the Cretaceous.
Fossil representation: Numerous individuals
including juveniles.
Although
discovered in 1972, Gallimimus was a relatively
little known
dinosaur until its appearance in the 1993 movie blockbuster
Jurassic Park. In one of the more famous scenes of
this film a whole
herd of Gallimimus gets chased by the Tyrannosaurus
before one slips and
is killed by this predator. Although science fiction, this scene
might not be too far off the mark as a tyrannosaur
named Tarbosaurus
did roam Mongolia at the same time as Gallimimus
and there has been
speculation that Tarbosaurus might actually
represent an Asian species
of Tyrannosaurus.
Gallimimus
is what is called an ornithomimid
dinosaur, a group of specially
adapted lightweight theropods that became one of the more common
dinosaur types towards the end of the Cretaceous period. Of these
Gallimius was one of if not the biggest of the
group, often credited
at being six meters long but with other fossil material indicating a
larger size of up to eight meters long. Mongolia seems to have had
the right conditions for freak giant dinosaur genera with another
example being Gigantoraptor,
a giant oviraptorid when compared to
other dinosaurs of its kind. To date the only other contenders for an
even larger ornithomimids are Beishanlong
and Deinocheirus.
Key
to the survival strategy of Gallimimus, and other
ornithomimids,
was speed. The legs especially the lower portions were long and
capable of covering a lot of ground with each stride. The bones like
in all theropods were hollow in order to reduce the overall weight of
the body so that less energy was required to move and faster running
speeds could be maintained. The main body however was proportionately
longer than other related genera, and this may have had an impact
upon how tight Gallimimus could turn. This may
not have been so
much of a hindrance however as much of Mongolia during the Cretaceous
was open arid plain and realistically all Gallimimus
would have to do
to survive would be to outpace their potential predators.
Like
with all ornithomimids, there is no universal agreement upon what
Gallimimus actually ate. The overall size of the
skull is small in
proportion to the body, but the snout is still longer than most other
ornithomimids. The jaws were fashioned into a toothless keratinous
beak, and without teeth of a certain kind, it is impossible to
establish what Gallimimus ate without the evidence
of stomach remains
to give further clues. One thing that can be established is that the
‘beak’ could have been used to either pick out plant parts, or
even pick up small animals. The size of the skull while small was
still large enough to pick up small lizards, snakes and even mammals
that realistically would have had to be swallowed whole since there
were no teeth to process the bodies. Additionally the point of
articulation in the jaws was so rigid that Gallimimus
could do little
more than open and close its mouth. If Gallimimus
and other
ornithomimids did indeed hunt small animals then they may have killed
them by picking them up and throwing them hard against the ground in a
similar way to how South American seriema birds do today (which are
also seen to being analogous to the phorusrachid
terror birds that
lived after the dinosaurs). A final dietary option for Gallimimus
would be to raid the nests of other dinosaurs for eggs.
Gallimimus
also had long arms and fingers, features that could have been used
for raking up plants from the ground or perhaps even grasping other
things such as eggs so that Gallimimus could run
and eat away from the
attentions of angry parents. One possible counter against the
predatory hypothesis is that Gallimimus had eyes
that faced out to
either side rather than forwards. This means that Gallimimus
had a
very wide field of view with which it would have had an easier time
spotting threats, but lacked the detailed depth perception that is a
hallmark of specialised predatory animals. Despite this however,
the nearest living analogy, birds, often have this eye arrangement
yet are still capable of hunting other small animals and invertebrates.
Because
juvenile Gallimimus have been found, it is
possible to get an idea of
how this genus and other ornithomimids as a group developed over
different life stages. It now also seems that Gallimimus
and
ornithomimds in general may have had primitive downy feathers that
insulated their bodies, however it is still uncertain if fully grown
adult Gallimimus retained feathers, as the larger
an animal gets,
the less it needs hair or feather to the point where the presence of
these features may actually become a hindrance.
A
second species of Gallimimus (G.
mongoliensis) was suggested
by Rinchen Barsbold in 1996, but in 2006 Barsbold changed
his mind and declared the remains to be an as yet unknown ornithomimid
dinosaur.
Further reading
- A new dinosaur, Gallimimus bullatus n. gen., n.
sp. (Ornithomimidae)
from the Upper Cretaceous of Mongolia. - Palaeontologia Polonica 27:
103-143. - H. Osm�lska, E. Roniewicz & R. Barsbold - 1972.
- X-ray microanalysis of fossil dinosaur bone: age differences in the
calcium and phosphorus content of Gallimimus bullatus bones. - Folia
Histochemica et Cytobiologica. 25 (3–4): 241–244. - R. Pawlicki
& P. Bolechała - 1987.- X-ray microanalysis of fossil dinosaur
bone: age differences in lead, iron, and magnesium content. - Folia
Histochemica et Cytobiologica. 29 (2): 81–83. - R. Pawlicki &
P. Bolechała - 1991.
- Lower jaw of Gallimimus bullatus, by J. Hurum. -
In, Mesozoic
Vertebrate Life. Bloomington: Indiana University Press. pp. 34–41. - D.
H. Tanke, K. Carpenter & M. W. Skrepnick (eds.) - 2001.
- Ornithomimids from the Nemegt Formation of Mongolia. - Journal of the
Paleontological Society of Korea. 22 (1): 195–207. - Yoshitsugu
Kobayashi & Rinchen Barsbold - 2006.
- Theropod trackways associated with a Gallimimus
foot skeleton from
the Nemegt Formation, Mongolia. Palaeogeography, Palaeoclimatology,
Palaeoecology. 494: 160–167. - Hang-Jae Lee, Yuong-Nam Lee, Thomas L.
Adams, Philip J. Currie, Yoshitsugu Kobayashi, Louis L. Jacobs
& Eva B..Koppelhus - 2018.
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