Fossil range: Early Cretaceous
Tianyulong confuciusi, from the Early Cretaceous of China.
| Scientific classification
Tianyulong (named for the Shandong Tianyu Museum of Nature where the holotype fossil (STMN 26-3) is housed) is a genus of basal heterodontosaurid ornithischian dinosaur. The fossil represents a sub-adult individual, approximately 1 meter long. It is notable for the row of long, filamentous integumentary structures apparent on the back, tail and neck of the fossil. The similarity of these structures with those found on some derived theropods suggests their homology with feathers and raises the possibility that the earliest dinosaurs and their ancestors were covered with analogous dermal filamentous structures that can be considered as primitive feathers (proto-feathers). The only species is T. confuciusi, whose remains were discovered in Jianchang County, Western Liaoning Province, China, from a formation belonging to the Jehol group and dating from the Berriasian stage of the Early Cretaceous.
The holotype consists of an incomplete skeleton preserving a partial skull and mandible, partial presacral vertebrae, proximal–middle caudal vertebrae, nearly complete right scapula, both humeri, the proximal end of the left ulna, partial pubes, both ischia, both femora, the right tibia and fibula and pes, as well as remains of long, singular and unbranched filamentous integumentary structures. The holotype is from a subadult individual that probably measured 70 cm in length based on the proportions of the South African related genus Heterodontosaurus.
Tianyulong is classified as being a basal member of the heterodontosaurid family, a group of small ornithischian dinosaur characterized by a slender body, long tail and a pair of enlarged canine-like tusks. They were herbivorous or possibly omnivorous. Until the discovery of Tianyulong, known members of the group were restricted to the Early Jurassic of South Africa and North America, with possibly one additional genus (Echinodon) from the Early Cretaceous of England. Tianyulong therefore firmly established the existence of heterodontosaurids during the Early Cretaceous and extends their geographical range to Asia.
The filamentous integumentary structures are preserved on three areas of the fossil: in one patch just below the neck, another one on the back, and the largest one above the tail. The hollow filaments are parallel to each other and are singular with no evidence of branching. They also appear to be relatively rigid, making them more analogous to the integumentary structures found on the tail of Psittacosaurus than to the proto-feather structures found in avian and non-avian theropods. Among the theropods, the structures in Tianyulong are most similar to the singular unbranched proto-feathers of Sinosauropteryx and Beipiaosaurus. The estimated length of the integumentary structures on the tail is about 60 mm which is seven times the height of a caudal vertebra. Their length and hollow nature argue against of them being subdermal structures such as collagen fibers.
Such dermal structures have previously been reported only in derived theropods and ornithischians, and their discovery in Tianyulong extends the existence of such structures further down in the phylogenetic tree. However, the homology between the ornithischian filaments and the theropods proto-feathers is not obvious. If the homology is supported, the consequence is that the common ancestor of both saurischians and ornithischians were covered by feather-like structures and that groups for which skin impression are known such as the sauropods were only secondarily featherless. If the homology is not supported, it would indicate that these filamentous dermal structures evolved independently in saurischians and ornithischians, as well as in other archosaurs such as the pterosaurs. The authors (in supplementary information to their primary article) noted that discovery of similar filamentous structures in the theropod Beipiaosaurus bolstered the idea that the structures on Tianyulong are homologous with feathers. Both the filaments of Tianyulong and the filaments of Beipiaosaurus were long, singular, and unbranched. In Beipiaosaurus, however, the filaments were flattened. In Tianyulong, the filaments were round in cross section, and therefore closer in structure to the earliest forms of feathers predicted by developmental models.
- ^ Zheng Xiao-Ting, You Hai-Lu, Xu Xing, and Dong Zhi-Ming
- ^ Most dinosaurs that have fossil evidence of feathers are saurischian. In 2002, Psittacosaurus fossils were uncovered that had a plume of bristles jutting from its tail. Many other ornithischian dinosaurs may have possessed feathers, but their poor fossil preservation in many cases has prevented the feathers being recorded in the fossil record. See Feathered dinosaurs and Psittacosaurus for more details.
- ^ a b Zheng, Xiao-Ting; You, Hai-Lu; Xu, Xing; Dong, Zhi-Ming (19 March 2009). "An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures". Nature (journal) 458 (7236): 333-336. doi:10.1038/nature07856.
- ^ "Tianyulong". Pharyngula. PZ Myers. March 20, 2009. http://scienceblogs.com/pharyngula/2009/03/tianyulong.php. Retrieved on 2009-04-30.
- ^ Mayr, Gerald; Peters, D. Stephan; Plodowski, Gerhard; Vogel, Olaf (August 2002). "Bristle-like integumentary structures at the tail of the horned dinosaur Psittacosaurus". Naturwissenschaften (Heidelberg: Springer Berlin) 89 (8): 361–365. doi:10.1007/s00114-002-0339-6.
- ^ Currie, Philip J.; Pei-ji Chen (2001). "Anatomy of Sinosauropteryx prima from Liaoning, northeastern China". Canadian Journal of Earth Sciences (NRC Canada) 38 (12): 1705–1727. doi:10.1139/cjes-38-12-1705.
- ^ Xu, Xing; Zheng Xiao-ting; You, Hai-lu (20 January 2009). "A new feather type in a nonavian theropod and the early evolution of feathers". Proceedings of the National Academy of Sciences (Philadelphia). doi:10.1073/pnas.0810055106. PMID 19139401.
- Ed Yong (March 18, 2009). "Tianyulong - a fuzzy dinosaur that makes the origin of feathers fuzzier".