Description and Classification

Selimissus is considered to be a relatively small to medium-sized ornithopod dinosaur. Paleontologists estimate its adult length to have been between 3 to 4 meters (approximately 10 to 13 feet) and it likely weighed around 150 to 200 kilograms (330 to 440 pounds). It was probably a bipedal herbivore, capable of moving relatively quickly to evade predators. Its skeletal structure, inferred from fragmentary remains, suggests an agile build with a long tail for balance.

Classification-wise, Selimissus is placed within the Ornithopoda, a diverse group of herbivorous dinosaurs that also includes well-known genera like Iguanodon and Hadrosaurus. More specifically, it is thought to share affinities with early iguanodontians or perhaps more basal ornithopods, though its exact phylogenetic position remains uncertain pending more complete fossil discoveries. The type species is currently designated as Selimissus etmarshi, though this is based on the initial, limited findings.

Distinguishing Features

Based on the available fossil evidence, Selimissus is characterized by a combination of features rather than one single unique trait. These may include:

• A relatively elongated snout compared to some other basal ornithopods of similar size.
• Cheek teeth adapted for grinding tough plant material, with a specific pattern of wear facets.
• Slender hind limbs suggesting it was a capable runner.
• Vertebrae in the tail that show evidence of ossified tendons, which would have provided stiffness for balance, similar to those seen in Hypsilophodon or early iguanodontians.

Paleoenvironment and Diet

The geological context of Selimissus fossils suggests it lived in a diverse Late Cretaceous ecosystem. This environment was likely characterized by warm, humid conditions with abundant plant life, including forests, open woodlands, and riverine habitats. Selimissus would have shared its world with a variety of other dinosaurs. These could have included large theropods such as tyrannosaurids like Albertosaurus, other herbivorous dinosaurs such as horned ceratopsians like Chasmosaurus, and armored ankylosaurs.

As an ornithopod, Selimissus was a herbivore. Its dental structure indicates it primarily fed on low-growing vegetation, possibly ferns, cycads, and early flowering plants. Its agility would have been beneficial for foraging in denser undergrowth and for escaping predation.

Significance and Ongoing Research

While currently known from limited material, Selimissus is significant because it potentially adds to our understanding of the diversity and distribution of smaller ornithopod dinosaurs in North America during the Late Cretaceous. Discoveries of dinosaurs like Selimissus help paleontologists build a more complete picture of ancient food webs and ecological niches.

Ongoing research aims to uncover more complete fossil specimens of Selimissus. Such discoveries would be crucial for confirming its classification, refining our understanding of its anatomy and lifestyle, and exploring its evolutionary relationships with other ornithopods like Thescelosaurus or Parksosaurus. Further fieldwork in the regions where its fossils were found is hoped to yield more material that could shed light on this lesser-known dinosaur genus.