Dilong

Dilong is a genus of small, basal tyrannosauroid dinosaurs that roamed the Earth during the Early Cretaceous period. The sole species, Dilong paradoxus, is known from fossils discovered in the Yixian Formation of what is now China. The discovery of Dilong was a landmark event in paleontology, providing the first concrete evidence of feathers in the tyrannosauroid lineage, a characteristic previously only suspected for the group.

Discovery and Naming

The holotype specimen of Dilong was unearthed in the Lujiatun Unit of the Yixian Formation, with geological dating placing the rocks between 125.8 and 126 million years old. The genus was formally described by Xu Xing and colleagues in 2004. The name "Dilong" is derived from the Chinese words 'dì' meaning 'emperor' and 'lóng' meaning 'dragon,' a nod to its evolutionary connection to the famed 'king' tyrannosaurid, Tyrannosaurus rex. The species name, paradoxus, is a Latinization of the Greek word for 'against received wisdom,' reflecting the surprising finding of feathers.

Physical Characteristics and Paleobiology

Dilong was a relatively small dinosaur, with the type specimen measuring approximately 1.6 meters (5.2 ft) in length. It is believed to have been a juvenile, with estimates suggesting fully grown adults could exceed 2 meters (6.6 ft) and weigh around 6 kg (13 lb). The fossilized remains reveal that Dilong possessed simple feathers or protofeathers, observed in skin impressions near the jaw and tail. These were likely for insulation, as they were not structured for flight. Braincase analysis indicates Dilong had an S-shaped brain and a large flocculus, suggesting agility and good balance. However, its olfactory tracts were small, implying a less developed sense of smell compared to later tyrannosaurids like Tyrannosaurus rex. There is speculation that feathers might have been shed as the animal grew larger, with adult tyrannosauroids perhaps relying more on scales.

Classification

Initial classification placed Dilong as one of the earliest and most primitive members of Tyrannosauroidea. However, subsequent phylogenetic analyses have yielded varied results, with some studies positioning it as a proceratosaurid or even outside the Tyrannosauroidea clade, while others continue to support its placement within the group.