Revised May 11, 2017 with new nesting for Chiappeavis.
Once again, taxon exclusion issues arise
Colleagues, we have to let the taxa nest themselves. Don’t restrict your inclusion sets to the short list of taxa you prefer! In the Jianianhualong paper a long list of candidate taxa were excluded, including its actual proximal sisters (Fig. 6). And they missed the other big headline that should have attended this new taxon. See below.
Xu et al. 2017
bring us a new genus of theropod dinosaur with feathers, Jianianhualong tengi (DLXH 1218; Yixian Formation, Early Cretaceous; Fig. 1). They nested their new find in an unresolved clade including the non-bird troodontid, Sinornithoides (Fig. 5). Notably they did not resolve Solnhofen birds (‘Archaeopteryx’ specimens), troodontids and dromaeosaurids. That should have been a red flag that more effort was needed to weed out bad scores in their matrix. Maybe a reconstruction would have helped? (Fig. 3).
in the large reptile tree (LRT, 1004 taxa) Jianianhualong tengi nests strongly with sapeornithid birds, despite its long bony tail, short forelimbs and large size, all atavistic traits retained in this one of the first flightless birds and certainly one of the first large flightless birds. This aspect was overlooked by Xu et al. 2017 as they mistakenly considered this a feathered non-bird troodontid. It is a bird. A big flightless bird.
If you think the long tail of Jianianhualong is an issue…
Archaeopteryx recurva (the Eichstaett specimen) nests with Jianianhualong and it has a long bony tail, too.
If you think the large size of Jianianhualong is an issue…
think of it like an early ostrich, flightless with no sternum, a giant Archaeopteryx in the Early Cretaceous, running from more primitive dinosaur-eating theropods.
Xu et al. did not test taxa that actually nest closer to Jianianhualong, using an antiquated matrix with only two Solnhofen birds. Xu et al. report, “The discovery of Jianianhualong provides direct evidence for the presence of pennaceous feathers in an unquestionable troodontid theropod.” Since all birds are troodontids in the LRT this statement is true. However, Xu et al. were not thinking that birds arose from troodontids (Fig. 5), so this became a surprising discovery for them. As in so many other cases discussed herein, character traits come as no surprise when the taxon in question is correctly nested.
I just add taxa
and the software/cladogram does the rest. No initial bias. Reconstructions help. So does colorizing the bone. In this case, at least, working from the photo with DGS was more instructive and better able to demonstrate observations to others than traditional firsthand access labeled with small two-letter abbreviations.
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 (Figs. 1, 6). So, asymmetry is not exceptional, but expected. Xu et al. reported, “Most significantly, the taxon has the earliest known asymmetrical troodontid feathers, suggesting that feather asymmetry was ancestral to Paraves.” The entire statement is false under the present hypothesis of interrelationships.
The unfortunate return of ‘modular evolution.”
Xu et al cite references to the concept of ‘modular (mosaic) evolution‘ which is based on invalid phylogeny. Please avoid ‘modular evolution’. That’s not how evolution works in the real world.
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.