Description and Classification

Velocisaurus was a relatively small dinosaur, estimated to be about 1.2 to 1.5 meters (4 to 5 feet) in length and very lightly built. Its most notable features are found in its slender hind limbs, particularly the foot, which suggest it was well-adapted for running. The tibia (shin bone) was long, which is common in animals built for speed. Due to the incomplete nature of its fossils (only parts of the hind limb are known), its full appearance is somewhat speculative, but it would have been a bipedal carnivore, walking and running on its two hind legs.

Velocisaurus belongs to the group Theropoda, which includes most carnivorous dinosaurs. More specifically, it is classified within the family Noasauridae. Noasaurids were a diverse group of ceratosaurian theropods that lived primarily in the Southern Hemisphere (Gondwana) during the Cretaceous period. Other members of this family include Noasaurus, which had a distinctive claw on its foot, and Masiakasaurus from Madagascar, known for its unusual forward-pointing teeth. The features of Velocisaurus‘s foot bones are key to its placement within Noasauridae and help scientists understand the variety of body types within this group.

Distinguishing Features

Velocisaurus can be identified by several unique characteristics of its hind limb, especially its foot:

• Its metatarsals (the long bones in the foot that connect the ankle to the toes) were specialized for running. The middle metatarsal (metatarsal III) was significantly larger and more robust than the second and fourth metatarsals which were very slender. This indicates that the third toe bore most of the animal’s weight, a feature seen in fast-running animals.
• The upper end of the third metatarsal had a distinct, somewhat triangular shape in cross-section.
• The tibia (shin bone) was long and slender, contributing to a long stride length relative to its body size.
• Overall, its hind limb structure points to a cursorial (running-adapted) lifestyle.

Paleoenvironment and Diet

The fossils of Velocisaurus were discovered in the Bajo de la Carpa Formation of Neuquén Province, Argentina. During the Late Cretaceous, this area was a semi-arid environment with seasonal rivers and floodplains. Velocisaurus shared this habitat with a variety of other dinosaurs, including large sauropods like Bonitasaura, abelisaurid theropods such as Aucasaurus, and other small theropods and reptiles. The presence of a fast-running dinosaur like Velocisaurus suggests an ecosystem with open spaces where speed would be an advantage for hunting or escaping predators.

As a theropod, Velocisaurus was a carnivore. Given its small size and gracile build, it likely preyed on small animals such as lizards, early mammals, insects, and perhaps the young of other dinosaurs. Its speed would have allowed it to chase down agile prey effectively. It was not a large predator and would have occupied a different ecological niche than the larger abelisaurids in its environment.

Significance and Ongoing Research

Velocisaurus is significant because it provides important information about the diversity of small theropod dinosaurs in South America during the Late Cretaceous. Its specialized foot structure is a key example of how different dinosaur groups evolved adaptations for running and locomotion. It helps paleontologists understand the evolutionary relationships and adaptations within the Noasauridae family, showing that some members were slender, fast runners.

Ongoing research on Velocisaurus is limited by the scarcity of its fossil remains. The discovery of more complete skeletons would be invaluable for understanding its full anatomy, proportions, and how it lived. Paleontologists continue to study the known fossils, comparing them with new discoveries of related noasaurids like Berthasaura, to refine its classification and shed more light on the evolution and paleobiogeography of these fascinating Gondwanan theropods. Further biomechanical studies on its foot structure could also provide more precise details about its running capabilities.