Dilong paradoxus
- 演化之聲
- 2 days ago
- 3 min read
Updated: 1 day ago
Age
Cretaceous（Valanginian-Barremian）
139-128 Ma
Taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Clade: Coelurosauria
Superfamily: Tyrannosauroidea
Clade: Pantyrannosauria
Genus: Dilong
Species: Dilong paradoxus
Morphological description
Dilong paradoxus was a small, slender basal tyrannosauroid theropod. Known specimens indicate a body length of about 1.6 m, with relatively long forelimbs and a three-fingered hand.
The skull possessed several tyrannosauroid features, including two large pneumatic recesses dorsal to the antorbital fossa, a Y-shaped crest formed by the nasals and lacrimals, and a lateral projection anterior to the basal tuber on the basisphenoid. In addition, the interspinous ligamentous fossae of the cervical vertebrae were deep and subcircular, the distal end of the scapula was expanded, and the coracoid was proportionally large.
Etymology
Genus name Dilong: derived from the Chinese 帝龍, with di meaning "emperor" and long meaning "dragon."
Species name paradoxus: derived from Latin, meaning "unexpected" or "paradoxical."
Biological description
Dilong paradoxus lived in what is now western Liaoning, China, during the Early Cretaceous, and is known from the Yixian Formation, dated to approximately 128 to 139 million years ago. This region formed part of the Jehol Biota, an exceptionally fossil-rich ecosystem characterized by frequent volcanic activity and fine-grained sedimentation such as volcanic ash and fine sand. These rapid burial conditions enabled the preservation of soft tissues and skin-related structures, yielding unusually valuable paleontological information. From an evolutionary perspective, Dilong paradoxus represents an early stage in tyrannosauroid history before the group evolved into giant-bodied predators.
The filamentous integumentary structures preserved in Dilong paradoxus are generally interpreted as protofeathers. These structures occur near the lower jaw and tail, demonstrating that feather-like body coverings had already evolved in early tyrannosauroids. This evidence substantially altered the older view that tyrannosauroids were uniformly covered in scales.
The most widely discussed function of these protofeathers is thermoregulation. Because Dilong paradoxus was relatively small, it would have lost body heat more readily and therefore likely benefited from additional insulation. Researchers have suggested that such feather-like coverings may have been especially important in juveniles or other small-bodied individuals. As tyrannosauroids grew larger and their need for insulation decreased, these structures may have been reduced or lost, with scales becoming the dominant body covering instead. This raises the possibility that tyrannosauroids may have changed in external appearance through growth. It has also been proposed that different regions of the body may have carried different kinds of integument, with feathers in some areas and scales in others rather than a single uniform covering.
In terms of classification, some phylogenetic analyses have at times placed Dilong paradoxus among more derived coelurosaurians, but most studies continue to support its position as a basal member of Tyrannosauroidea. This uncertainty itself reflects the transitional nature of its anatomy, as the skeleton combines features characteristic of tyrannosauroids with traits more typical of more basal coelurosaurians.
Studies based on endocast reconstructions of the cranial cavity have also suggested that the brain of Dilong paradoxus differed from that of later giant tyrannosaurids. Its forebrain appears to have been relatively elevated, followed by a flexed middle region and a hindbrain extending posteroventrally, producing a more curved overall configuration. This contrasts with the straighter brain profile seen in later large tyrannosaurids. Accordingly, as tyrannosauroids evolved into gigantic apex predators, the form and spatial arrangement of the central nervous system also appear to have changed substantially, likely in association with shifts in sensory processing and motor control.
（Author: Shui-Ye You）
References
Kundrát M et al. (2020). Evolutionary disparity in the endoneurocranial configuration between small and gigantic tyrannosauroids. Historical Biology.
Shih C et al. (2019). Coexisting Animals and Plants in the Ecosystems. Rhythms of Insect Evolution: Evidence from the Jurassic and Cretaceous in Northern China, First Edition.
Xu X et al. (2004). Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids. Nature.
41.82, 120.77
Comments