NGMC 91

Fossil cast

NGMC 91, nicknamed “Dave”, is an as-yet unnamed, substantially complete, fossil of a small dromaeosaurid dinosaur from the Early Cretaceous Yixian Formation of Liaoning, China. The specimen is in the collection of the National Geological Museum of China. It was collected in Fanzhangzi quarry, near Lingyuan City, Liaoning Province. This location is part of the Dawangzhangzi fossil beds, which have been dated to about 122 million years ago, during the early Aptian age.^[1] A specimen of the fish Lycoptera is also preserved near the foot.

Description

Feathers

NGMC 91 is notable for its extensive preservation of various types of feathers. First, several filaments were joined together into "tufts", like the structure of down feather. Second, a row of filaments (barbs) were joined together to a main shaft (rachis), making them similar in structure to normal bird feathers. While they do not preserve the tiny hooks (barbules) that modern feathers have, which allow the feathers of modern birds to form a discrete vane, discrete vanes are visible in the feathers of the forelimbs, hindlimbs and tail, suggesting that barbules must have been present in life. The feathers covered the entire body, including the head in front of the eye, the neck, wing-like sprays on the arms, long feathers on the thighs, and a lozenge-shaped fan on the tail like that of Archaeopteryx.^[2]

Classification

NGMC 91 was first described in a paper published in the journal Nature by Ji Qiang and colleagues in 2001. They declined to name the specimen because, although the specimen is completely articulated, almost all of the bones shattered when the fossil slabs were split, so that only the silhouettes of theses bones are clear in most of the part and counterpart. This obscured diagnostic skeletal features, which made the specimen's genus uncertain. They noted that it was similar in some respects to Sinornithosaurus millenii, and they suggested that the differences between the two could have been due to age.^[2] Ji, along with another team of scientists, further emphasized this similarity in a 2002 paper, in which they formally referred the specimen to Sinornithosaurus, though they considered the exact species questionable.^[3] Meanwhile, Stephen Czerkas and colleagues considered the specimen to represent an example of their newly described species Cryptovolans pauli (now usually considered a synonym of Microraptor gui), based on supposed wing proportions.

Phylogenetic studies did not support the idea that NGMC 91 was a close relative of S. millenii. In a 2004 analysis, Phil Senter and colleagues found that it was, in fact, more closely related to Microraptor.^[4] Subsequent studies, also by Senter, have continued to show support for this finding despite the fact that some data used in the original study was later found to be flawed.^[5]

References

1. ^ Zhou, Z. (2006). "Evolutionary radiation of the Jehol Biota: chronological and ecological perspectives." Geological Journal, 41: 377–393.
2. ^ ^{a b} Ji Q., Norell, M.A., Gao K.Q., Ji S.-A. and Ren, D. (2001). "The distribution of integumentary structures in a feathered dinosaur." "Nature", 410(6832): 1084-1087.
3. ^ Ji Q., Ji S.-A., Yuan C.-X. and Ji X.-X. (2002). "Restudy on a small dromaeosaurid dinosaur with feathers over its entire body." Earth Science Frontiers, 9(3): 57-63.
4. ^ Senter, Phil; Barsbold, R.; Britt, Brooks B.; Burnham, David B. (2004). "Systematics and evolution of Dromaeosauridae (Dinosauria, Theropoda)". Bulletin of the Gunma Museum of Natural History 8: 1–20. 
5. ^ Senter, P. (2007). "A new look at the phylogeny of Coelurosauria (Dinosauria: Theropoda)." Journal of Systematic Palaeontology, 5: 429–463. doi:10.1017/S1477201907002143.

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