Description and Classification

Nemegtonykus was a small, lightly built theropod dinosaur, estimated to be about 1 meter (3.3 feet) in length and weighing only a few kilograms. Like other members of the Alvarezsauria group, it had a slender body, long legs adapted for running, and very short but strong arms. The most notable feature of its forelimbs was a single, large, robust claw on what would be equivalent to a thumb or second finger, while its other fingers were tiny. It is widely believed that Nemegtonykus, similar to other coelurosaurian dinosaurs such as Compsognathus or Sinosauropteryx, was likely covered in feathers. However, direct fossil evidence of feathers has not yet been found for this specific genus.

In terms of scientific classification, Nemegtonykus belongs to Alvarezsauria, a peculiar family of small, long-legged, and short-armed theropods. Within this group, it is placed in the subfamily Parvicursorinae, which includes other advanced alvarezsaurids. Its closest known relatives likely include other Asian alvarezsaurids such as Mononykus, which was also found in the Nemegt Formation, and Shuvuuia. These dinosaurs represent a specialized branch of theropods that developed unique features, especially in their forelimbs.

Distinguishing Features

Nemegtonykus can be identified by several key characteristics, many of which it shares with other parvicursorine alvarezsaurids, though with unique combinations or slight differences:

• Extremely short forelimbs that possessed only one functional, enlarged claw on the innermost digit (digit I, or the “thumb” if compared to a human hand, though it’s considered digit II by some paleontologists based on its development). The other digits on the hand were significantly reduced.
• The functional claw was robust and strong, suggesting it was used for powerful actions like digging or tearing, possibly to get into insect nests.
• Slender hind limbs with elongated foot bones (metatarsals), indicating adaptations for swift running. The foot structure is described as subarctometatarsalian, where the upper part of the middle metatarsal bone is somewhat compressed by the bones on either side, a feature often linked to fast movement.
• While the skull of Nemegtonykus is not known from the original fossil specimen, related alvarezsaurids like Shuvuuia had small skulls with many tiny, peg-like teeth. This suggests that Nemegtonykus also likely had such teeth, suited for a diet of small prey items.

Paleoenvironment and Diet

Nemegtonykus lived in the environment that is now preserved as the Nemegt Formation, dating to the Maastrichtian stage of the Late Cretaceous. This area of ancient Mongolia featured a wetter climate than other Gobi Desert environments of the time, with a landscape of river channels, floodplains, and lakes, supporting relatively lush vegetation. This rich ecosystem was home to a diverse array of dinosaurs. Nemegtonykus would have shared its habitat with giant plant-eating sauropods like Nemegtosaurus, large duck-billed hadrosaurs such as Saurolophus and Barsboldia, and the fearsome apex predator Tarbosaurus, a close relative of Tyrannosaurus rex. Other contemporaries included swift ostrich-mimic dinosaurs like Gallimimus, the giant and unusual Deinocheirus, as well as various oviraptorosaurs like Nemegtomaia, dome-headed pachycephalosaurs like Homalocephale, and armored ankylosaurs such as Tarchia.

The specialized anatomy of Nemegtonykus, especially its single-clawed hand, strongly suggests it had a diet primarily consisting of insects. Paleontologists believe that alvarezsaurids were myrmecophagous, meaning they likely fed on social insects like ants and termites. The strong, single claw could have been an effective tool to rip open termite mounds, tear bark from trees to expose insect colonies, or dig into the ground for larvae. The presumed small, weak teeth (based on those of its relatives) would have been suitable for consuming such small invertebrates rather than larger prey.

Significance and Ongoing Research

The discovery of Nemegtonykus is important because it adds to the known diversity of alvarezsaurian dinosaurs, particularly from the well-studied fossil beds of the Nemegt Formation. It helps paleontologists better understand the evolutionary spread and ecological roles of these unique theropods during the final stages of the dinosaur era in Asia. The original fossil specimen, even though incomplete, provides valuable information about its anatomy, especially its limbs, which helps in clarifying the relationships between different members of the Alvarezsauria group.

Ongoing research on Nemegtonykus and its kin focuses on several areas. Scientists continue to analyze its skeletal features to gain more insights into how it moved and what its feeding mechanics might have been. Comparing Nemegtonykus with other alvarezsaurids, such as its contemporary Mononykus or the slightly older Shuvuuia and Parvicursor, helps to reveal patterns in alvarezsaur evolution and how different species might have coexisted or specialized in different food sources within the same environment. The search for more complete fossil material of Nemegtonykus, particularly a skull, remains a key goal, as this would provide a much fuller understanding of this dinosaur. Future research will also aim to pinpoint its exact position in the alvarezsaur family tree and to better understand its role in the complex Nemegt ecosystem.