Li et al. 2020 used various frequencies of light
and spectroscope technology on the holotype bones and feathers of Jianianhualong (Figs. 1, 2; Early Cretaceous, Xu et al. 2020, DLXH 1218) to identify specific elements in the matrix and specimen.
From the abstract:
“Here, we carried out a large-area micro-X-Ray fluorescence (micro-XRF) analysis on the holotypic specimen of Jianianhualong tengi via a Brucker M6 Jetstream mobile XRF scanner.”
Figure 1a. Jianianhualong, Serikornis and Jurapteryx to scale.
Figure 1b. Jianianhualong tengi in situ. This is the largest among the early birds, a fact overlooked by the Xu et al. 2017. Think of Jianianhualong as a giant Archaeopteryx!
From the abstract:
“Jianianhualong tengi is a key taxon for understanding the evolution of pennaceous feathers as well as troodontid theropods, and it is known by only the holotype, which was recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China.”
What they didn’t do is to rerun their phylogenetic analysis with more taxa (Fig. 2).
What they didn’t do is to create a reconstruction, perhaps using DGS to precisely trace and segregate the bones to rebuild the skeleton (Figs. 1, 3, 4).
Figure x. Subset of the LRT focusing on birds and their ancestors. Jianianhualong nests within Aves (five taxa from the bottom).
in the large reptile tree (LRT, 1730+ taxa) Jianianhualong nests within Aves (five taxa from the bottom of Fig. 2) even though it was clearly not volant due to its much larger size and smaller forelimbs. Close relatives include Archaeopteryx (= Jurapteryx) recurva (= Eichstätt specimen, Fig. 3) and the privately held #11 specimen of Archaeopteryx.
The authors think Jianianhualong is a troodontid.
According to Wikipedia, “A number of characteristics allow Jianianhualong to be identified as a member of the Troodontidae. These include:
- the long forward-projecting branch and flange of the lacrimal bone; [✓]
- the foramina on the nasal bone; [?]
- the smooth transition between the eye socket and the backward-projecting branch of the frontal bone; [✓]
- the ridge on the forward-projecting branch of the jugal bone; [✓]
- the triangular dentary bearing a widening groove; [✓]
- the robust forward-projecting branch of the surangular bone; [✓]
- the relatively large number of unevenly-distributed teeth; [✓]
- the flattened chevrons with blunt forward projections and bifurcated backward projections; [✓]
- and the broad and flat “pubic apron” formed by the pubic bones.” [?]
Figure 2. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.
Professor Larry Martin would be so proud!
Why? Because the Wikipedia author (above) is using a list of traits to support an hypothesis of interrelationships rather than using a cladogram to support that hypothesis. Checkmarks [✓] indicate traits Jurapteryx shares. Question marks [?] indicate traits not shown in Jianianhualong or Jurapteryx. Or did I miss something?
The problem is,
various authors add taxa to the Troodontidae that don’t belong there in the LRT, as we learned earlier here. The LRT; subset Fig. x) recovers Jiaianhualong as the largest known member of the Sapeornis/Jurapteryx clade of birds. Several flightless birds are in this clade. These could be confused with troodontids for that reason. In the LRT the clade Troodontidae include Sinornithoides + Sauronithoides their LCA and all derived taxa. None of these are direct bird ancestors.
Getting back to chemistry
“The bone in Jianianhualong is, as expected rich in calcium and phosphorus, corresponding mineralogically to apatite. The regions where feather remains can be observed show an enrichment and correlation pattern of several elements including manganese, titanium, nickel and copper.”
FIgure 3. GIF animation of the skull of Jianianhualong showing original tracing in line art and colorized bones (DGS) used to create a reconstruction (Fig. 3).
Jianianhualong 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 expected, not exceptional. This is the earliest known large flightless bird, not an example of the invalid hypothesis of ‘mosaic’ evolution.
Figure 4. Reconstruction of the skull of Jianianhualong based on DGS tracings in figure 2.
Liaoningventor curriei (Shen et al. 2017; DNHM D3012; Early Cretaceous) was also originally described as a non-avian troodontid, but nests with Jianianhualong as a flightless bird.
Li J, et al. (8 co-authors 2020. Micro-XRF study of the troodontid dinosaur Jianianhualong tengi reveals new biological and taphonomical signals. bioRxiv 2020.09.07.285833 (preprint) PDF doi: https://doi.org/10.1101/2020.09.07.285833
Shen C-Z, Zhao B, Gao C-L, Lü J-C and Kundrat 2017. A New Troodontid Dinosaur (Liaoningvenator curriei gen. et sp. nov.) from the Early Cretaceous Yixian Formation in Western Liaoning Province. Acta Geoscientica Sinica 38(3):359-371.
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.