Wednesday 31 October 2012

The fate of the Sleeping Dragon.

In October 2004 Xing Xu of the Institute of Vertebrate Paleontology & Paleoanthropology at the Chinese Academy of Sciences and Mark Norell of the American Museum of Natural History published a paper in the journal Nature describing a remarkable Early Cretaceous Troodontid Dinosaur, preserved in volcanic ash in what appears to be a sleeping position. The Dinosaur was named Mei long, meaning Sleeping Dragon. It was a 53 cm long animal, preserved with its tail wrapped around it, and its head tucked under one forelimb, in a manner reminiscent of a sleeping Bird.

Mei long, the Sleeping Dragon. Abbreviations: (cev) cervical vertebrae; (cv) caudal vertebrae; (dv) dorsal vertebrae; (fu) furcula; (lac) left astragalus–calcaneum; (lc) left coracoid; (lf) left femur; (lh) left humerus; (li) left ilium; (lm) left manus; (lp) left pubis; (lpe) left pes; (lr) left radius; (ls) left scapula; (lt) left tibia; (lu) left ulna; (pg) pelvic girdle; (rac) right astragalus–calcaneum; (rc) right coracoid; (rf) right femur; (rh) right humerus; (ri) right ilium; (rm) right manus; (rp) right pubis; (rpe) right pes; (rr) right radius; (rs) right scapula; (ru) right ulna; (sk) skull. Scale bar equals 2 cm. Xu & Norell (2004).

A similar position had previously been observed in another small Troodontid, Sinornithoides youngi (Young's Chinese birdy-thing), described in October 1993 by Dale Russell of the North Carolina Museum of Earth Sciences, and Zhi-Ming Dong of the Institute of Vertebrate Paleontology & Paleoanthropology at the Chinese Academy of Sciences, in a paper in the Canadian Journal of Earth Sciences, though this specimen was less complete, making the diagnosis of the 'roosting position' less obvious. Like Mei long this specimen had been buried in this position, this time in wind-blown sand.

Computed tomography scan image of Sinornithoides youngi. D'Urso, Thompson & Earwaker (2000).

In a paper published in the journal Paleobiology in March 2007, Cynthia Marshall Faux of the Department of Paleontology at the Museum of the Rockies and Kevin Padian of the Department of Integrative Biology and Museum of Paleontology at the University of California, Berkeley disputed the sleeping analysis of Mei long and Sinornithoides youngi, suggesting that their position might instead be a reflexive position caused by reflexive curving of the spine due to muscle spasming during asphyxiation, rather than a sleeping pose.

In a paper published in the journal PLoS One on 27 September 2012, a team of scientists led by Chunling Gao of the Dalian Natural History Museum describe the discovery of a second specimen of Mei long, preserved like the first in an apparent roosting position, and discuss the implications of this study.

The new Mei long specimen. Abbreviations: (aofe) antorbital fenestra; (c) cervical vertebra(e) unnumbered; (c6) sixth cervical vertebra; (c7) seventh cervical vertebra; (ca1–ca18) caudal vertebrae (one through eighteen); (co) coracoid; (d) dentary; (dv) dorsal vertebra(e); (f) frontal; (fm) femur; (fl) fibula; (h) humerus; (il) ilium; (l) lacrimal; (mt-II, mt-III), second metatarsal, third metatarsal etc.; (mx) maxilla; (mxfl?) maxillary fenestra; (n?) nasal; (nc) neural canal; (ns) neural spine; (o) orbit; (p) parietal; (pu) pubis; (pmx) premaxilla; (q) quadrate; (r) radius; (s1, s2, etc.) first sacral vertebra, second sacral vertebra etc.; (sa) surangular; (sc) scapula; (sp) fused neural spine of sacrum; (t) tibia; (u?) possible manual ungual; (ul) ulna; (II-2) second phalanx of digit II of pes; (II-3) third phalanx of digit II of pes; (III-1) first phalanx of digit III of pes; (IV-1–
IV-4) first through fourth phalanges of digit IV. Scale bar equals 1 cm. Gao et al. (2012).

Gao et al. observe that in human victims of asphyxiation the fingers are commonly found in a contorted position, and since three specimens of Troodontid Dinosaurs have now been found in an identical position, none of which show any sign of contorted digits, that it is reasonable to assume that the death position of the dinosaurs was not a result of asphyxiation. They do not, however rule out asphyxiation as a cause of death, observing that a number of bodies recovered from Pompeii appear to be sleeping peacefully, from which they conclude it may be possible to asphyxiate in a deep sleep without undergoing reflexive muscle contortions. They suggest that since the Dinosaurs were killed in a way that did not disturb them from their sleeping position (which would certainly be the case if they were interred by a volcanic lahar or similar) then they may have died within burrows, enabling the bodies to be preserved without exposure to weathering elements or the activities of scavengers.

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