Tianyulong
| Tianyulong Temporal range: Early Cretaceous
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| Genus: | Tianyulong Xiao-Ting Zheng, Hai-Lu You, Xing Xu & Zhi-Ming Dong, 2009
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Tianyulong (Etymology: from the Shandong Tianyu Museum of Nature where the holotype fossil is housed) is a genus of heterodontosaurid ornithischian dinosaur known to have a row of long filamentous integumentary structures on its back, tail and neck. 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 Early Cretaceous.[1]
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 impressions 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.
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[2] and Beipiaosaurus. The estimated length of the integumentary structures on the tail is about 60 mm which is 7 times the height of a caudal vertebrae. 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. However, their discovery in Tianyulong extends their existence further down in the phylogenetical tree. However, the homology between the ornithischian filaments and the theropods proto-feathers is far from 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.
Reference
- ^ Zheng, X-.T.,H.-L. You, X. Xu & Z.-M. Dong (2009). "An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures." Nature, 458, pp. 333-336.
- ^ Currie, P. J. & Chen, P. J. (2001) "Anatomy of Sinosauropteryx prima from Liaoning, northeastern China.", Can. J. Earth Sci. 38, pp1705–1727.
Tianyulong - a fuzzy dinosaur that makes the origin of feathers fuzzier
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