An Ultimate Guide to Mononykus: The One Claw

Leave a comment / / Updated on: 22nd October 2023

Name Meaning“One claw”Height0.4-0.5 meters (1.3-1.6 feet)
PronunciationMo-noh-nee-kusLength1-1.2 meters (3.3-3.9 feet)
EraMesozoicLate CretaceousWeight3.5 kilograms (7.7 pounds)
ClassificationDinosauria, Saurischia & Theropoda LocationMongolia (Asia)

Mononykus Pictures

Mononykus was a theropod dinosaur that lived in Mongolia during the Cretaceous Period | CoreyFord via Getty Images

The Mononykus

Gage Beasley Prehistoric's Mononykus Concept
Gage Beasley Prehistoric’s Mononykus Concept

The discovery of the Mononykus raised multiple questions among scientists, particularly how closely related it is to modern birds.

No wonder the genus is now the main subject of multiple research papers which aim at describing it and outlining its link to modern birds.

The Mononykus was a small theropod that roamed prehistoric Mongolia.

More precisely, it lived about 70 million years ago during the Late Cretaceous.

This theropod may have had a feathered body, long, thin legs, and a specialized claw on each short forelimb, indicating it was an insectivore that fed by opening insect colonies.

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Physical Characteristics

Gage Beasley Prehistoric's Mononykus Concept
Gage Beasley Prehistoric’s Mononykus Concept

The Mononykus was a small alvarezsaurid theropod.

It measured only 1-1.2 meters (3.3-3.9 feet) long and weighed approximately 3.5 kilograms (7.7 pounds).

It was probably 0.4 meters (1.3 feet) tall at the hips.

Although this may come as a surprise, the Mononykus is among the largest members of the Alvarezsauridae family.

Many of its relatives are much smaller, not exceeding 50 centimeters (20 inches) long.

The Linhenykus, for example, was 50 centimeters (20 inches) long, weighed 500 grams (18 ounces), and had a femur length of only 7 centimeters (2.8 inches).

The Shuvuuia was slightly bigger but still smaller than the Mononykus, measuring 1 meter (3.3 feet) long.

However, although smaller, it weighed roughly the same – 3.5 kilograms (7.7 pounds).

Mononykus | Elenarts108 via Getty Images

The type species of the Alvarezsauridae family was a bit larger than the Mononykus, reaching 1.4 meters (4.6 feet) long.

Despite this, it was not as heavy, as it weighed only 3 kilograms (6.6 pounds).

The Mononykus can be distinguished from its close relatives by one pubic bone with a triangular cross-section, which is only one of its unique characteristics.

This small dinosaur had a long, elongated snout and small teeth.

Its hindlimbs were long, while the forelimbs were highly reduced, almost nonexistent.

Life Restoration of the Mononykus | PaleoNeolitic via Wikipedia (CC BY 4.0)

However, despite being extremely short, scientists say the forelimbs were unusually robust, and each bore a distinctive claw.

In fact, the members of the Alvarezsauroidea superfamily are known to have undergone significant modifications of hand morphology.

These changes can likely be associated with digging adaptations, and they may have been of help in searching for insects beyond the tree bark.

A study shows that the enlarged first digit known from the Mononykus is a major indicator that this theropod is a close relative of extant birds.

A close relative is known to have been feathered, and while paleontological discoveries didn’t confirm this aspect for the Mononykus, specialists argue that this may be a characteristic of other members of this group.

Habitat and Distribution

The holotype specimen was discovered in the Nemegt Formation; it was unearthed from the Bügiin Tsav locality.

However, although its fossils were found only in this location, we cannot rule out the possibility that the Mononykus was actually widespread across Asia or at least throughout the areas surrounding the Bügiin Tsav locality.

The Nemegt Formation is located in the Mongolian Gobi Desert, and it is thought to have been a wet environment featuring a forest cover.

It was likely filled with shallow lakes, streams, and floodplains where sandstones and mudstones were deposited.

Aerial view of the Bayanzag flaming cliffs at sunset in Mongolia, found in the Gobi Desert | Mik122 via Getty Images

The Mononykus lived sometime between the end of the Campanian and the beginning of the Maastrichtian.

A high sea level and a warm and humid climate characterize the Campanian.

During the Maastrichtian, however, the world started to shift to an arid and colder climate. 

Fossil evidence shows that the Nemegt Formation supported the growth of araucarians (coniferous trees), duckweeds (flowering aquatic plants), and pondweeds (freshwater plants).

Behavior and Diet

Mononykus dinosaur hunting an insect in the desert | Mik122 via Getty Images

The Mononykus was a bipedal theropod, and while its forelimbs weren’t used for walking, they helped it get the required amount of food to survive.

The limbs had one long claw, which measured approximately 7.5 centimeters (3 inches) long.

A study on the function of the Mononykus forelimbs indicates that they were not specialized in either grasping prey or digging burrows.

Instead, they were excellent for hook-and-pull movements or scratch-digging.

Mounted Mononykus holotype at the Giga Dinosaur Exhibition 2017, Japan | Kumiko via Flickr (CC BY-SA 2.0)

As such, it has been suggested that the Mononykus was an insectivore that filled the same ecological niche as pangolins and anteaters.

This makes it even more bizarre because such an ecological niche is unusual in dinosaurs.

It may have also used its claws to crack open the eggshells discovered in oviraptorid nests.

Studies on the Shuvuuia revealed that it may have been nocturnal, and although this hasn’t been confirmed, we cannot rule out the possibility of a nocturnal lifestyle since the two were close relatives. 

Life Cycle

Mononykus | CoreyFord via Getty Images

Like all dinosaurs and modern birds, the Mononykus reproduced by laying eggs.

Females likely had two functional oviducts, so they probably laid eggs in pairs.

Apart from this, very little is known about the life cycle and reproductive behavior of the Mynonykus.

Since no fossilized nests or eggs were discovered, scientists know little about its nesting and incubation behavior.

Moreover, while it is known that many dinosaur hatchlings were precocial, meaning they were born quite developed and could feed themselves, it is unknown whether this is also valid for the Mononykus.

Evolution and History

Mononykus dinosaur walking in the desert next to tamaris trees | Elenarts108 via Getty Images

The earliest theropods were the Eodromaeus carnivores and the herrerasaurids (Herrerasauridae).

The Eodromaeus was alive 231.4-229 million years ago during the Late Triassic and roamed the territory we now call Argentina.

The herrerasaurids are thought to have appeared approximately 233 million years ago and gone extinct 228 million years ago.

Today, scientists are still debating which of the two was the earliest.

Alvarezsaurs are widely recognized as the most basal group of the Maniraptora clade of the Theropoda group.

Mononykus dinosaur running by night surrounded with cycadeodia plants | Elenarts108 via Getty Images

The Mononykus is now classified in the Mononykini tribe of the Alvarezsauridae family, and it is the second-described genus of the family after the Alvarezsaurus.

As such, while the Alvarezsaurus is considered a primitive (basal) member, the Mononykus is considered an advanced (derived) member.

The first and only Mononykus fossils were recovered in 1987 in the Mongolian Gobi Desert, consisting of a partial skeleton.

The creature was first named and described in 1993, and the genus was named Mononychus.

Mononykus dinosaur standing in white background- 3D render | Elenarts108 via Getty Images

However, shortly after, it was renamed Mononykus, as Mononychus was already taken by a beetle.

Over the years, paleontologists discovered other fossils attributed to it, which were later reassigned to the Shuvuuia genus.

Another specimen that had been recovered years before the discovery of the holotype may belong to the Mononykus, and it is now in the collection of the American Museum of Natural History.

Nevertheless, considering many fossils were mistakenly attributed to it, scientists aren’t sure this bird-like specimen belongs to the genus.

Interactions with Other Species

Oviraptosaur surrounded with small Mononykus dinosaurs in the mountain | Elenarts108 via Getty Images

The Nemegt Formation is a rich fossil site, indicating that the creatures living there were likely never bored, as they had enough company!

Here’s a comprehensive list of the creatures the Mononykus may have shared its habitat with:

  • Amphibians like Altanulia
  • Crocodylomorphs like Paralligator
  • Various fish
  • Invertebrates like Candona, Cyclocypris, Limnocythere, and Nemegtia
  • Mammals like Buginbaatar
  • Pterosaurs like azhdarchids
  • Turtles
  • Ankylosaurs like Tarchia
  • Other alvarezsaurs like Nemegtonykus
  • Birds like Brodavis, Judinornis, and Teviornis
  • Dromaeosaurs like Adasaurus
  • Ornitomimosaurs like Deinocheirus and Gallimimus
  • Oviraptorosaurus like Avimimus, Elmisaurus, and Gobiraptor
  • Pachycephalosaurs like Homalocephale
  • Sauropods like Brontopodus, Nemegtosaurus, and Opisthocoelicaudia
  • Tyrannosaurs like Alioramus, Raptorex, and Tarbosaurus

The degree to which the Mononykus interacted with other creatures in its ecosystem remains unknown.

A group of Mononykus | CoreyFord via Getty Images

However, we may suppose that the Mononykus may have served as prey for carnivorous dinosaurs, at least for some of them, like the famous Tarbosaurus, which was almost as strong as the T-Rex.

Still, no evidence shows that the Tarbosaurus preyed on dinosaurs like the Mononykus.

Moreover, it may have been a scavenger, not an active predator.

Cultural Significance

Mononykus skeleton, AMNH | Thomas Cowart via Flickr (CC BY 2.0)

Many traits observed in the Mononykus show that it is more closely related to extant birds than the Archaeopteryx.

As such, its discovery marks a significant event in the universe of paleontology, as it carries important information about the evolution of birds.

Some studies label it as a transitional genus between primitive maniraptorans and modern birds.

It is no wonder that the Mononykus is now of major interest to paleontologists.

On the other hand, despite its popularity in the world of science and prehistory, it is not a frequent appearance in the media, indicating that many dinosaur enthusiasts may not yet be acquainted with this bizarre creature.


The Mononykus, otherwise known as the one claw, lived in the Mongolian Gobi Desert 70 million years ago.

It shared its habitat with many other prehistoric creatures.

This small dinosaur was an alvarezsaurid theropod known for having highly reduced forelimbs bearing a large claw likely used to open termite mounds or ant colonies.

The Mononykus probably had an elongated snout, small teeth, and long hind limbs that may have helped it move quickly.

This ancient creature is now an important genus in the Theropoda clade, carrying essential information about bird evolution.


Is Mononykus a bird?

The Mononykus is a dinosaur closely related to modern birds.

However, it is not a bird.

Is the Mononykus related to the anteater?

The Mononykus is not related to the anteater, but it is thought to have filled the same ecological niche during the Late Cretaceous.


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