Mei long 2 in Gao et al. 2012: an Early Cretaceous flightless bird, not a troodontid.

Taxon exclusion mars this otherwise wonderful study
from Gao et al. 2012 of a second Mei long (Fig. 1) found earlier (note the curled in situ specimen in gray, museum number DNHM D2154; in Fig. 1) from the Early Cretaceous of China.

Figure 1. Two Mei long specimens, one in vivo, one in situ.  Click to enlarge.
Figure 1. Two Mei long specimens, one in vivo, one in situ.  

Gao et al. report,
“A second nearly complete, articulated specimen of the basal troodontid Mei long (DNHM D2154) is reported from the Early Cretaceous (Hauterivian-Valanginian) lower Yixian Formation, Liaoning Province, China.”

Unfortunately
the large reptile tree (LRT, 1870+ taxa; subset Fig. 3) nests Mei long far from any troodontids.

If only Gao et al. would have added appropriate taxa.
Here (Fig. 2) are the closest relatives of Mei long within the bird clade Scansoriopterygidae (Fig. 3). Note that some still have long, folding forelimbs replete with feathers. Mei long was more like a small ostrich in the Early Cretaceous. Click HERE to enlarge the image on another web page.

Figure 1. Click to enlarge. Scansoriopterygids to scale.
in the LRT to scale.

Mei long
(IVPP V12733, Xu and Norell 2004, Early Cretaceous) is famous for its 3D preservation in a curled up sleeping posture. Originally considered a young juvenile, bird-like troodontid, Mei long nests in the large reptile tree between the xx specimen of Archaeopteryx and Scansoriopteryx amid the scansoriopterygid basal birds. A second specimen, DNHM D2154 (Gao et al. 2012), was also preserved in a sleeping posture. Mei is derived from a sister to the Munich specimen of Archaeopteryx and was basal to other scansoriopterygids.


Figure 3. Subset of the LRT focusing on basal theropods, including Mei, nesting here in orange within the Scasoriopterygidae following several Solnhofen birds (=Archaeopteryx).
Figure 4. From Gao et al. 2012. Colors added to match figure 3.

References
Gao C, Morschhauser EM, Varricchio DJ, Liu J and Zhao B 2012. A Second Soundly Sleeping Dragon: New Anatomical Details of the Chinese Troodontid Mei long with Implications for Phylogeny and Taphonomy. PLoS ONE 7(9): e45203. doi:10.1371/journal.pone.0045203

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