Description and Classification

Zephyrosaurus was a relatively small, bipedal herbivore. It is estimated to have been about 1.8 meters (6 feet) long and may have weighed around 20 to 30 kilograms (44 to 66 pounds). It walked and ran on its two hind legs, using its long tail for balance. Like other ornithopods, it had a beak for cropping vegetation and teeth further back in its jaws for chewing.

The classification of Zephyrosaurus places it within the group Ornithischia (bird-hipped dinosaurs) and specifically within Ornithopoda. Ornithopods were a diverse group of plant-eating dinosaurs that included well-known genera like Iguanodon and the hadrosaurs or “duck-billed” dinosaurs. Zephyrosaurus is considered a more basal, or early-diverging, member of this group. It was initially thought to be part of the Hypsilophodontidae family, but this group is now considered by many scientists to be an unnatural grouping. More recently, Zephyrosaurus has been linked to the Thescelosauridae family, which includes other small North American ornithopods like Thescelosaurus and its close relative, Orodromeus. Some studies suggest it might be part of a group known as Orodrominae, alongside Orodromeus and the burrowing dinosaur Oryctodromeus.

Distinguishing Features

Zephyrosaurus possessed several unique characteristics that help paleontologists identify it:

• A prominent, somewhat triangular boss (a raised, roughened area of bone) on the jugal bone, which is the cheekbone located below the eye. The exact function of this boss is not fully understood but might have been for display, species recognition, or related to jaw muscle attachments.
• A steeply angled face when viewed from the side.
• Possible adaptations for digging or burrowing, suggested by the robust nature of some of its bones and its close relationship to Oryctodromeus, a known burrower. However, direct fossil evidence of burrows associated with Zephyrosaurus has not yet been found.
• Relatively long lower leg bones, indicating it was likely a swift runner capable of evading predators.

Paleoenvironment and Diet

Zephyrosaurus lived in what is now Montana during the Early Cretaceous. The Cloverly Formation, where its fossils were found, represents an environment with floodplains, river systems, and open woodlands. The climate was likely seasonal, with periods of wet and dry weather. Zephyrosaurus shared this environment with a variety of other dinosaurs. These included the large predatory theropod Acrocanthosaurus, the smaller raptor-like dinosaur Deinonychus, the armored nodosaur Sauropelta, and the large ornithopod Tenontosaurus. Sauropods like Sauroposeidon also roamed this area.

As an ornithopod, Zephyrosaurus was a herbivore. Its diet likely consisted of low-growing plants such as ferns, cycads, and primitive flowering plants. Its beaked snout would have been used to nip off vegetation, which was then processed by its cheek teeth.

Significance and Ongoing Research

Zephyrosaurus is significant because it helps paleontologists understand the diversity and evolution of small ornithopod dinosaurs in North America during the Early Cretaceous. Its unique skull features, particularly the jugal boss, provide important anatomical information for comparing it with other related dinosaurs like Orodromeus and Thescelosaurus.

Ongoing research on Zephyrosaurus focuses on several areas. Scientists continue to search for more complete fossil material, which would provide a clearer picture of its full anatomy and lifestyle. Further studies of its bone structure may help determine if it possessed adaptations for burrowing, similar to its relative Oryctodromeus. Understanding the relationship between Zephyrosaurus and other ornithopods helps to map out the evolutionary tree of these plant-eating dinosaurs. The study of Zephyrosaurus contributes to a broader understanding of the ecosystems and animal communities of the Early Cretaceous period.