Description and Classification

Notohypsilophodon was a relatively small herbivorous dinosaur, estimated to have been about 1.3 to 1.5 meters (approximately 4 to 5 feet) in length and lightly built. Like other ornithopods of its kind, it walked on its two hind legs and was likely a quick and agile runner, which would have helped it escape from predators. Its forelimbs were shorter and probably used for grasping vegetation or for support when resting.

Notohypsilophodon belongs to the group Ornithopoda, which includes a diverse range of plant-eating dinosaurs such as duck-billed hadrosaurs and iguanodontians. More specifically, Notohypsilophodon is considered a basal (or primitive) member of this group. Its exact placement within Ornithopoda is still subject to some scientific discussion, but it shares characteristics with other early ornithopods. It is significant for representing a type of small herbivore present in Gondwana (the ancient southern supercontinent) during the Late Cretaceous.

Distinguishing Features

While the fossil remains of Notohypsilophodon are incomplete, consisting of parts of the vertebral column, limbs, and pelvis, scientists can identify several features:

• Relatively small size, typical of basal ornithopods.
• Bipedal posture, meaning it primarily walked and ran on its hind legs.
• Slender hind limbs adapted for swift movement.
• Specific anatomical details in its femur (thigh bone) and other limb bones, such as the shape and placement of muscle attachment points, help distinguish it from other related dinosaurs.
• Like other ornithopods, it would have possessed a horny beak for cropping plants and cheek teeth for grinding them, although skull material for Notohypsilophodon itself has not been extensively described.

Paleoenvironment and Diet

Notohypsilophodon lived in what is now Patagonia, Argentina, during the Late Cretaceous period. The fossils were found in the Bajo Barreal Formation, which indicates an environment of coastal plains and river systems with a relatively warm climate. This area would have supported a variety of plant life, forming the diet of Notohypsilophodon. As an herbivore, it likely fed on low-growing vegetation such as ferns, cycads, and early flowering plants.

It shared its environment with a diverse range of other dinosaurs. These included large sauropods like Sarmientosaurus and Epachthosaurus, which were also found in the Bajo Barreal Formation, as well as various predatory theropod dinosaurs such as abelisaurids and potentially megaraptorans that would have posed a threat to smaller animals like Notohypsilophodon.

Significance and Ongoing Research

The discovery of Notohypsilophodon is important because it adds to our understanding of ornithopod diversity in the Southern Hemisphere during the Cretaceous period. Small ornithopods are not as commonly found in Gondwanan fossil sites as they are in Laurasia (the northern supercontinent), making each discovery valuable. Notohypsilophodon provides evidence that these types of dinosaurs were present and part of the ecosystems in ancient South America.

Ongoing research focuses on better understanding its anatomy and its evolutionary relationships to other ornithopods, particularly other Gondwanan forms such as Gasparinisaura and Anabisetia. More complete fossil discoveries, especially of the skull, would greatly help to clarify its features and its place within the ornithopod family tree. Studying dinosaurs like Notohypsilophodon helps paleontologists piece together a more complete picture of the complex prehistoric world and how different dinosaur groups evolved and spread across the globe.