April 4, 2022 Scott Kraus

Avimimus was a Bird-like Theropod from the Cretaceous

Avimimus (pronounced AH-vee-MIME-us) was a feathered theropod dinosaur that lived about 95 million years ago during the late Cretaceous period in what is now Mongolia. It’s name comes from the Greek words meaning “bird mimic” because of its distinction as the first discovered dinosaur, with so many features like modern day birds, but still having enough theropod characteristics to be more dinosaur than bird. The Avimimus could be seen as an intermediary link between avian and dinosaur evolution. When originally discovered in the 1970s, the Avimimus was considered to be a descendant of the Archaeopteryx, but this was later disproved by evidence pointing to Avimimus’ more primitive bone composition and structure, making him part of a new class of bird-like dinosaur, the oviraptor family.

Quick Facts

What did Avimimus Look Like?

Avimimus was an interesting creature, like a modern ostrich or roadrunner. It was a two-legged feathered theropod, capable of running from predators, but not flight. The dinosaur was smaller than an ostrich, at only 3 to 4 feet tall. It is known from remains excavated from Mongolia that the Avimimus had a short rounded beak, placed on a relatively large head for its size. It also had abnormally large eyes, presumably to be able to detect predators or possibly insects as prey.  It supported its head on a long slender neck and used its feathered tail to balance itself when running.

Physical Characteristics of Avimimus

Not being able to fly might seem a disadvantage when compared to other dinosaurs, but the Avimimus  had some useful adaptions of its own.  First of all it was smart, scientists at least know that the brain of the Avimimus  was very large relative to its size, and that it was well protected by a bony skull.  Avimimus would need these smarts to evade predators and catch prey on the ground.  The legs of the Avimimus were longer than its other relatives in the Avimimidae family, indicating that it was a flightless bird long enough to evolve specialist running limbs. It ran on three toed feet, a characteristic known as digigrade.

What Kind of Environment Did Avimimus Live In?

The area where paleontologists found Avimimus was much different at the time they found the dinosaur than it would have been when it lived. The unique habitat of the late Cretaceous period was starkly different from both the time before, when its Oviraptor relatives lived and in the time after. The long clawed toes on the legs of Avimimus are just one indication to scientists that its habitat was something of a wet, marshy forested region. Evidence that Avimimus lived in large flocks also suggests of a wetlands environment. Gregarious birds, and indeed all animals, love to gather around water such as ponds and marshes.

What did Avimimus Eat?

Avimimus has variously been labeled as herbivore, omnivore, and insectivore. Scientists haven’t been able to infer very much about an Avimimus diet from the fossil records except for what they know from other Oviraptors, the larger category Avimimus belongs to of bird-like theropods from Mongolia. Like other Oviraptors, Avimimus was probably an omnivore. Its mouth was a toothless beak that could have been used to scavenge for a variety of food. Sergei Kurzanov, the scientist who first described Avimimus speculated that, since the upper portion of its beak had a serrated edge, there was a good chance that it ate insects. It would have also been useful for tearing into vegetation. Another idea for its diet is that it stole the eggs of other animals. This theory comes from its status as an Oviraptor, which actually means “egg stealer”. The consensus among paleontologists is usually that Avimimus is an omnivore.

How did Avimimus Move?

With its similarity to the modern roadrunner, Avimimus was likely capable of fast and extended running. It was a bipedal with two very long slender legs. The proportions of the thigh bones also indicate that it was fast. The skeletons show that the shin bones were proportionately longer than the thighs, which is just like modern cursorial birds that spend most, to all, of their time running along the ground. Muscle scars found on leg bones also indicate that Avimimus specialized in running.

Avimimus Did Not Fly much, if at All

Kurzanov believed that Avimimus was capable of weak flight. Feathers had not been found on the specimens that he wrote about, but quill knobs were present. The hand bones were fused together like modern birds and he interpreted a ridge on the lower arm bone as having had feathers attached to it. He also pointed out that the joints of the skeletons were exactly like birds, but other features indicated that the wings were too short to sustain flight. He called it a cursorial bipedal theropod and compared it’s ability to fly to that of a chicken, only  employing weak flight occasionally for hunting or when in danger. Today however, many paleontologists don’t believe it was capable of any flight at all. Morphological evidence of Avimimus tends to indicate that the dinosaur was adapted for moving along the ground.

Disagreement on Feathers and a Tail

Although paleontologists did not agree with Sergei Kurzanov about whether Avimimus could fly, there is consensus that it did have feathers. They were probably used for either insulation or perhaps a colorful plumage in mating. He was shown to be mistaken about believing Avimimus had no tail, though. At the time of his description of the dinosaur, there was no evidence of a tail, but since then fossil evidence of a short tail has been discovered.

The Discovery of Avimimus

During the summer of 1973, the Joint Soviet-Mongolian paleontological expedition found a mostly complete specimen of the new genus and species Avimimus portentosus. They found the theropod skeleton at Udan-Sayr in the southern Gobi of Mongolia. This was a major discovery due to the fact that it was the first dinosaur found with distinctive and significant amounts of bird-like features. It was also the first theropod with its particular hip structure. These new features caused the paleontologists to create a new family to categorize it, the Avimimidae family.

An Amazing Bird-like Dinosaur

Sergei Kurzanov, a Russian paleontologist who was part of the expedition, described the dinosaur in 1981. Upon it’s initial discovery, it was thought to be a bird until further study and subsequent fossil discoveries later in the 70s indicated that it was really a theropod with bird features. He named it Avimimus portensosus, which translates to “portentous bird mimic”. Portentous means to elicit amazement, but the meaning of the root word “portent” is also apt. Portent is a sign of things to come, just like Avimimus was only the beginning of discoveries of dinosaurs with strikingly bird-like features.

Avimimus Bone Bed Discovery

An exhibition of Mongolian, Canadian, and American paleontologists reported that they found a gathering of at least 10 Avimimus skeletons in one spot, also called a bone bed. The discovery was significant not just because of the sheer number of specimens but because of what it tells us about how the dinosaur lived. Since there was little variation in the size of the specimens, it indicates that they were gregarious creatures, or flocked together. There was also muscle scarring on the leg bones, providing evidence that the dinosaur was capable of fast and prolonged running.

The Importance of Avimimus

The discovery of Avimimus signaled a breakthrough in paleontologists understanding of dinosaurs and their connection with birds. It was the first dinosaur to show such distinctively bird-like features and in such large numbers. In the years since it was first discovered it has been a challenge for paleontologists to categorize, showing similarities to birds and multiple categories of dinosaur. Usually Avimimus is considered an Oviraptor and an important link between dinosaurs and birds.