About Dilong
| Scientific Name (Genus) | Dilong |
| Meaning of Name | Emperor dragon |
| Classification | Saurischia, Theropoda (Coelurosauria) Formerly considered a basal tyrannosauroid, but recent studies suggest it may be placed outside this group. |
| Total Length | Approx. 1.6 - 2m |
| Diet | Carnivorous |
| Period | Early Cretaceous (approx. 126 million years ago) |
| Sub-classification / Species Name | Dilong paradoxus |
| Year of Paper Publication | 2004 |
| Genus Name Publication |
Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids.
Nature. 431 by Xu, X., Norell, M. A., Kuang, X., Wang, X., Zhao, Q., Jia, C. 2004. |
Features
Dilong is a small theropod described in a 2004 paper. The discovery of the first evidence of feathers in a tyrannosauroid relative sent shockwaves through the paleontological community at the time.
The genus name Dilong means "emperor dragon," derived from the Chinese words for "emperor" and "dragon," indicating its lineage leading to the later king of dinosaurs.
Furthermore, the only species of Dilong was named paradoxus. This Latinized word from ancient Greek means "contrary to expectations, paradoxical." It stems from the surprise that a relative of Tyrannosaurus, synonymous with giant reptiles, was small and had feathers.
The discovered skeleton fossil was of a juvenile about 1.6m long, but it is estimated that even adults were only about 2m long and weighed around 10kg.
The shape of its skull and teeth clearly possessed features of tyrannosauroids. For instance, the premaxillary teeth (front upper teeth) had a "D-shaped" cross-section and were tightly packed. This was a powerful weapon suited for efficiently scraping meat off prey. Additionally, it had a "Y-shaped" crest on its snout, another feature leading to later large tyrannosaurids.
Left: Dilong, Right: Tyrannosaurus
Thus, while the head shows advanced features leading to the later dinosaur king, the proportions of the body and arms retained many primitive characteristics.
The "Primitive Feathers" that Overturned the Image of Tyrannosauroids
The most groundbreaking aspect of Dilong's discovery was the clear presence of "protofeather" traces left around its jaw and tail. Protofeathers are simple, filamentous structures lacking the complex form of modern bird feathers.
These feathers were not for flight, but are thought to have been primarily for insulation (retaining body heat). This fact indicates that Dilong was not a cold-blooded animal dependent on external temperatures, but a warm-blooded animal capable of maintaining its own body heat.
There was once a time when people thought, "Does this discovery mean that the giant Tyrannosaurus rex was also completely covered in feathers?" However, it is now believed that because a larger body size makes it harder to lose heat (gigantothermy), they lost their feathers as they grew in order to dissipate excess heat. In fact, traces of scaly skin have been found in fossils of later massive tyrannosaurids.
Were Tyrannosaurus babies fluffy too?
Small dinosaurs like Dilong (about 10kg) and the babies of large dinosaurs lost body heat easily and needed insulating feathers. Since full-body feathers have also been found on its giant relative Yutyrannus (9m long), it seems they underwent complex evolution, growing or losing feathers depending on the climate and body size.
Agile Visual Hunter
Unlike later tyrannosaurs which had arms reduced to two fingers, Dilong possessed relatively long and large forelimbs (arms). Its hands had three fingers equipped with sharp claws. It seems it could firmly grasp prey with these arms while biting down with its powerful jaws.
Examining the leg bones reveals that it was in the intermediate stages of evolving a shock-absorbing, spring-like foot. It was specialized for agile directional changes and short-distance dashes rather than long-distance pursuit.
Furthermore, recent CT scans of its brain shape (endocast) revealed that the part controlling vision and balance (floccular lobe of the cerebellum) was highly developed. While the giant Tyrannosaurus was a hunter relying on its "sense of smell" to sniff out prey from afar, Dilong appears to have been a hunter that utilized excellent "vision" and "agility" in complex forests to visually track down and catch fast-fleeing prey.
The "Chinese Pompeii" and Ecology in a Cool Forest
Dilong fossils were discovered in the "Lujiatun Bed" in Liaoning Province, China. This site, where animals were buried alive in an instant by sudden volcanic mudflows, is also called the "Chinese Pompeii." Dilong's miraculous three-dimensional fossils were preserved thanks to these mudflows.
This region (Jehol Biota) during the Early Cretaceous (approx. 126 million years ago), when Dilong lived, featured rich forests densely grown with conifers and ferns, as well as lakes. The average temperature at the time was about 10°C, a cool climate for the dinosaur age, and it seems it even snowed in winter. This cool climate was a major reason why Dilong evolved insulating feathers.
This forest was inhabited by herbivorous dinosaurs such as Psittacosaurus, an ancestor of ceratopsians, as well as early mammals. Armed with excellent vision and quick movements, Dilong likely dashed through the forest hunting these small prey.
Dilong Stamp and Fossil Gallery
