Description and Classification

Patagonykus was a relatively small, two-legged dinosaur, estimated to be about 1 to 2 meters (3.3 to 6.6 feet) long and lightly built. It had long legs, suggesting it was a quick runner. One of its most striking features was its very short but strong arms. Each hand had a single, very large, and powerful claw on its thumb. The other fingers were tiny or might have been missing altogether. While some of its relatives had breastbones with a keel (a ridge for muscle attachment like in modern birds), the breastbone found for Patagonykus was flat, suggesting it was somewhat more primitive in this aspect within its group, though its arms were still built for strong movements.

Patagonykus belongs to the family Alvarezsauridae. Alvarezsaurids are a strange group of small, bird-like theropod dinosaurs known for their long legs and highly specialized arms. These dinosaurs are part of a larger group called Maniraptora, which includes birds and other dinosaurs closely related to birds, such as Velociraptor and Oviraptor. Other alvarezsaurid dinosaurs include Mononykus and Shuvuuia from Asia, and Alvarezsaurus, also from Argentina.

Distinguishing Features

Patagonykus can be identified by several key characteristics that set it apart from many other dinosaurs:

• Extremely short but very muscular forelimbs.
• A single, large, and sturdy claw on the first digit (the thumb) of each hand, while the other fingers were greatly reduced.
• Long, slender hind limbs adapted for fast running, with features in the foot bones that are common in running animals.
• A relatively long neck and a small head with likely small teeth (though the skull is not fully known for Patagonykus itself, this is inferred from its relatives).
• A somewhat stiffened tail, which could have helped with balance while running.

Paleoenvironment and Diet

Patagonykus lived in what is now the Patagonia region of Argentina, in an environment represented by the Portezuelo Formation. During the Late Cretaceous, this area was likely a semi-dry landscape with seasonal rivers and open plains. It shared this habitat with various other dinosaurs, including large sauropods like titanosaurs, meat-eating abelisaurids, and other small theropods.

The unique arms and large claw of Patagonykus and other alvarezsaurids strongly suggest a specialized diet. Scientists believe these dinosaurs were insectivores, meaning they ate insects. The powerful single claw might have been used like a pickaxe to break into termite mounds, ant nests, or to rip bark off trees to uncover insects and their larvae. Their small teeth, inferred from related species, would have been good for grabbing small, wriggling prey but not for tearing large pieces of meat.

Significance and Ongoing Research

The discovery of Patagonykus and its relatives has been very important for understanding the diversity of theropod dinosaurs. Alvarezsaurids showcase a unique evolutionary path with highly specialized bodies that are quite different from other meat-eating dinosaurs. They help scientists understand how varied dinosaur adaptations could be, particularly for finding food. Patagonykus also adds to our knowledge of the types of dinosaurs that lived in South America during the Late Cretaceous.

Ongoing research on alvarezsaurids like Patagonykus continues to explore their exact diet and how they used their strange arms and claws. Scientists are also working to better understand their evolutionary relationships with other theropods, especially their connection to the bird lineage. Finding more complete fossils of Patagonykus, especially skull material, would help confirm details about its diet and appearance. The study of these animals also sheds light on how different dinosaur groups adapted to various ecological niches before the mass extinction event that ended the Cretaceous period.