The origin of giant birds: Jianianhualong, a giant Jurapteryx (formerly Archaeopteryx)

We looked at this one
earlier here. Among the Solnhofen birds is Jurapteryx recurva (Figs. 1,2) and it nests with the many times larger Serikornis (Fig. 2) and the even larger Jianianhualong (Fig. 2).

Figure 3. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Figure 3. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Achaeopteryx (Jurapteryx) recurva (JM2257; the Eichstätt specimen; Howgate 1985) is one of the smaller Solnhofen birds. Here it nests as the last common ancestor of all extant birds. A gap spanning the entire Cretaceous separates this taxon from extant taxa and their kin. As in other bird lines, the loss of tail length, the fusion of the pygostyle and the fusion of manus elements are convergent.

Figure 2. Jianianhualong, Serikornis and Jurapteryx to scale.

Figure 2. Jianianhualong, Serikornis and Jurapteryx to scale.

 

Serikornis sungei (Lefèvre et al. 2017; Late Jurassic; 50cm long) was originally considered a pre-bird sister to Eosinopteryx. Here it nests with Jurapteryx, the Eichstätt specimen first attributed to ArchaeopteryxSerikornis is larger than its sister, had larger teeth and was flightless. 

Jianianhualong tengi (Xu et al. 2017; Early Cretaceous; DLXH 1218) originally considered a non-avian troodontid, Jianianhualong nests bertween Sapeornis and Archaeopteryx recurva. It is a troodontid-like bird, not a bird-like troodontid. Note the odd scapula shape, like that in Sapeornis. Note the retrovered pedal digit 1, showing this taxon was derived from perching birds. The tall naris and long tibia are autapomorphies.

Xu et al. 2014 made a headline out of the asymmetric feathers found with Jianianhualong. In the present context, Jianianhualong is derived from volant ancestors. So asymmetry is not exceptional, but expected. This is the earliest known large flightless bird.

References
Howgate ME 1985. Problems of the osteology of Archaeopteryx: is the Eichstätt specimen a distinct genus?. In Hecht, Ostrom, Viohl, and Wellnhofer (eds.), The Beginnings of Birds: Proceedings of the International Archaeopteryx Conference, Eichstätt 1984. Freunde des Jura-Museums Eichstätt, Eichstätt 105-112.
Lefèvre U, Cau A, Cincotta A, Hu D-Y, Chinsamy A, Escuillié F and Godefroit P 2017.A new Jurassic theropod from China documents a transitional step in the macrostructure of feathers. Sci Nat 104:74. DOI 10.1007/s00114-017-1496-y
Xu X, Currie P, Pittman M, Xing L, Meng QW-J, Lü J-C, Hu D and Yu C-Y 2017. Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features. Nature Communications DOI: 10.1038/ncomms14972.

wiki/Jurapteryx
wiki/Jianianhualong
wiki/Serikornis

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