Chongmingia manus: separating those overlapping phalanges

Chongmingia zhengi 
(Wang et al. 2016; Aptian, Early Cretaceous; Figs. 1–3) is a basal bird preserving the limbs and not much else. Earlier in 2017 I did not make a reconstruction because so little was preserved. That is remedied here (Figs 1, 2). The new reconstruction of Chongmingia corrects several errors made by Wang et al. 2016.

Figure 1. Chongmingia tracing from Wang et al. alongside a reconstruction of the elements.

Figure 1. Chongmingia tracing from Wang et al. alongside a reconstruction of the elements.

Wang et al. did not separate
the overlapping phalanges (Fig. 2). Nor did they separate the overlapping coracoid and scapula (Fig. 1). Nor did they recognize the disarticulated manual unguals (Fig. 2). Nor did they realize the ‘extra’ toe phalanx was a displaced finger phalanx (Fig. 1 the white phalanx).

Figure 2. Wang et al. did not separate the overlapping phalanges or recognize the manus unguals, or recognize the extra finger phalanx displaced near the toe phalanges.

Figure 2. Wang et al. did not separate the overlapping phalanges or recognize the manus unguals, or recognize the extra toe phalanx was a displaced finger phalanx.

Chongmingia nests at the base of the scansoriopterygid clade
in the large reptile tree (LRT, 1752+ taxa subset Fig. 4). That clade includes Yi, Ambopteryx, Scansoriopteryx (Fig. 3) and other birds with a longer manual digit 3 than 2. That distinct, but not unique, morphology is nascent in Chongmingia (Fig. 3).

From the Wang et al. 2016 abstract:
“The Chinese Lower Cretaceous Jehol Group is the second oldest fossil bird-bearing deposit, only surpassed by Archaeopteryx from the German Upper Jurassic Solnhofen Limestones. Here we report a new bird, Chongmingia zhengi gen. et sp. nov., from the Jehol Biota. Phylogenetic analyses indicate that Chongmingia zhengi is basal to the dominant Mesozoic avian clades Enantiornithes and Ornithuromorpha and represents a new basal avialan lineage.”

The LRT does not support this nesting, but does place Chongmingia at a basal node, within the Scansoriopterygidae between the #12 specimen (privately owned) assigned to Archaeopteryx and Mei.

Figure 3. Ambopteryx nests midway and is phylogenetically midway between the larger Yi and the smaller Scansoriopteryx. None of these taxa have an extra long bone in the arm.

Figure 3. Ambopteryx nests midway and is phylogenetically midway between the larger Yi and the smaller Scansoriopteryx. None of these taxa have an extra long bone in the arm.

Do not overlook
the continuing fact that only three long arm bones (humerus, radius and ulna) are present in Chongmingia and other scansoriopterygid clade members (Figs. 3, 4), not four (the misidentified bat-like styliform element arising from the wrist) as other bird workers say.

Figure 4. Subset of the LRT focusing on birds. Chongmingia is highlighted in yellow in the Scansoriopterygidae.

Figure 4. Subset of the LRT focusing on birds. Chongmingia is highlighted in yellow in the Scansoriopterygidae.

I am still waiting for someone, anyone
to identify four long arm bones in any scansoriopterygid. So far, no one has.


References
Wang M, Wang X, Wang Y and  Zhou Z 2016. A new basal bird from China with implications for morphological diversity in early birds. Nature Scientific Reports 6, art. 19700, 2016.

wiki/Chongmingia

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