Gallimimus

Astonishing Speed and Anatomy

Among ornithomimosaurs, Gallimimus is a large species, second only to Deinocheirus. It measured 4 to 6 meters (13.1 to 19.7 feet) in length, and when standing, its head reached over 2 meters (6.6 feet) high.
While its body size was more than double that of an ostrich, its skeletal structure was lightweight, giving it an estimated weight of only about 400 kg (880 lbs).

The Secret of Its Swiftness

True to its agile appearance, Gallimimus was a highly fleet-footed dinosaur.
With a light body and powerfully developed hind limbs, there are various theories about its top speed. It is estimated to have run at speeds of 45 to over 60 km/h (28 to over 37 mph), with some theories even suggesting it reached 110 km/h (68 mph), matching the speed of a cheetah.
This is a speed comparable to a passenger car driving on a standard road.

The secret to this astonishing speed lies in its unique foot structure.

Flexible Feet

Compared to its ancestral species, the three bones making up the instep of its foot were of different thicknesses.
This structure provided flexibility to the foot and served to cushion the impact when running.

Characteristics of Fast Animals

It possessed the anatomical features of fast-running animals, such as the length of its tibia (shinbone) relative to its body proportions.

A Balancer

Its long tail, which made up more than half of its body length, is believed to have served as a balancer while running.

Its long tail is believed to have served as a balancer while running.

Physical Characteristics and Alert Behavior

Gallimimus had a very small head and a long, slender neck and limbs, much like a bird.
However, among ostrich dinosaurs, it is noted for having a relatively long torso and comparatively shorter forelimbs.

Field of Vision

A 1988 study suggested that Gallimimus’s eyeballs did not move much within their sockets.
Like modern herbivores, its laterally positioned eyes provided a wide field of vision, but it was poor at seeing things in three dimensions (binocular vision).
Therefore, it could not survey its surroundings without moving its neck. It may have constantly bobbed and turned its head around to watch out for predators, much like an ostrich or a pigeon.

Intelligence

Fossilized skulls reveal that it had a large brain, leading researchers to believe that Gallimimus was a relatively intelligent dinosaur.

Life in a Herd

Because individuals of various growth stages have been found clustered together, it is highly likely that Gallimimus formed herds composed of members of different ages and lived collectively.
The scene in the movie “Jurassic Park” where a flock of them flees in a panic from a Tyrannosaurus is iconic, but no conclusive evidence has yet been found to prove that they actually ran around in herds all the time.

A Diet Shrouded in Mystery

Although classified as a theropod, Gallimimus was not a ferocious carnivorous hunter.
Its most defining feature was its mouth; its face was shaped like that of a modern duck, and it had absolutely no teeth in its mouth.

Its face was shaped like a duck’s, and it had absolutely no teeth in its mouth.

Because of this, its exact diet has been the subject of long-standing debate.

The Omnivore Theory (Currently Mainstream)

Today, many researchers lean toward the idea that it was “omnivorous”—meaning it was not specialized for one specific food type, but rather ate primarily plants while opportunistically consuming insects and small animals when available.

Beak and Forelimbs

Its mouth was covered by a toothless keratinous beak that was thin and sharp, a shape well-suited for catching insects, other small animals, lizards, and mammals.
It would also have been ideal for pecking open the eggs of other dinosaurs to drink the contents.

The Role of the Arms

Its arms were long, allowing it to easily grab plants growing on the ground, as well as mammals, lizards, and other small prey.
Its fingertips were unusually well-developed, and it is thought to have been dexterous enough to use its hands like hooks to pull tall grasses and branches toward itself to eat.

The Herbivore Theory

The discovery of what appear to be gastroliths (stomach stones) used for grinding plant matter in its stomach region also supports the possibility that it was a herbivore.
Since it lacked teeth, it is believed to have swallowed foods like nuts and seeds whole, digesting them with the help of the gastroliths in its stomach.

The Filter-Feeding Theory

In a 2001 study, it was suggested that its beak was equipped with a comb-like filter (slits)—the first such discovery in a dinosaur.
This led to the “liquid diet theory” gaining major attention, proposing that it filtered aquatic organisms and microbes in lakes and ponds, feeding much like a flamingo.
However, there are counterarguments based on examples like its close relative Struthiomimus, which was much larger than a waterfowl. Critics argue that filtering aquatic cyanobacteria and small animals alone would not have provided sufficient nutritional volume.

The Discovery of Feathers and “Wings”

For a long time, Gallimimus was depicted as being covered in scales, just as it appeared in the movie “Jurassic Park.”
However, recent research has completely transformed that image.

Traces of Feathers

While traces of feathers have not been found directly on Gallimimus fossils, they have been discovered on its very close relative, Ornithomimus.

The Existence of “Wings”

Most surprisingly, it was revealed that adult Ornithomimus possessed “wings” on their forelimbs made of fully developed feathers with central shafts (quills).
These wings were not for flying, but are thought to have been used for courtship displays or for keeping eggs warm.

Based on this discovery, it is now the scientific standard to believe that as Gallimimus grew, its body became covered in feathers like an ostrich, and it developed wings on its forelimbs.

Additionally, two species of Gallimimus have been identified: *Gallimimus bullatus* and *Gallimimus mongoliensis*.