A folded, wingless enantiornithine hatchling, IVPP V12707, enters the LRT

Updated May 13, 2022
with the nesting of Shenqiornis (Fig A) and the IVPP hatchling together sharing nearly all traits.

Figure A. Shenqiornis and the IVPP hatchling nest together in the LRT.

Wang et al. 2021 described a tiny Early Cretaceous
enantiornithine hatchling presently known only by its museum number, IVPP V12707 (Fig. 1). Uniquely, the back half of the specimen is folded over the front half, and the wings are missing. How does this happen? I have no idea. Phylogenetic bracketing indicates the wings were large.


Figure 1. IVPP V12707, an enantiornine hatchling close to Chiappeavis and Pengornis. Images from Wang et al. 2021. The specimen is unfolded below. The wings are not present. Shown almost twice life size on a 72 dpi monitor. The ectopterygoids (purple comma-shaped) are shown in two possible configurations here.

From the Wang et al. abstract:
“The transformation of the bird skull from an ancestral akinetic, heavy, and toothed dinosaurian morphology to a highly derived, lightweight, edentulous, and kinetic skull is an innovation as significant as powered flight and feathers. Our understanding of evolutionary assembly of the modern form and function of avian cranium has been impeded by the rarity of early bird fossils with well-preserved skulls.”

Not in the large reptile tree (LRT, 1873+ taxa; subset Fig. 2) where there are plenty of taxa to clearly demonstrate a very gradual transition from dinosaurian morphology to bird morphology.

It is also worth noting that Wang et al. decided the IVPP specimen had an akinetic palate without finding the palatines (Fig. 1 imagined in gray). Otherwise scorable palatal traits are no different than for related taxa in the LRT.

Figure 2. Subset of the LRT focusing on basal birds and the Enantiornithes. Note the IVPP hatchling does not nest with Gretcheniao in the LRT, as it does in Wang et al. 2019.

From the abstract:
“Here, we describe a new enantiornithine bird from the Early Cretaceous of China that preserves a nearly complete skull including the palatal elements, exposing the components of cranial kinesis. Our three-dimensional reconstruction of the entire enantiornithine skull demonstrates that this bird has an akinetic skull indicated by the unexpected retention of the plesiomorphic dinosaurian palate and diapsid temporal configurations, capped with a derived avialan rostrum and cranial roof, highlighting the highly modular and mosaic evolution of the avialan skull.”

Modular and mosaic evolution are two myths that need to be eliminated from the literature. Adding taxa gets rid of these concepts. Don’t be confused by convergence and reversal. The IVPP specimen does not have a dinosaurian skull, defined by Wang et al. as, akinetic. Perhaps the authors were thinking of ostriches, parrots and finches for their typical birds, rather shoebill storks, toucans, penguins and hummingbirds.

Wang et al. write,
“As in most other enantiornithines, the facial margin is dominated by the maxilla, rather than the premaxilla as in crown birds.”

Not true. The maxilla dominates the rostrum in many crown birds (just a few listed above).

Figure 3. Chiappeavis, Pengornis and STM-34-1 to scale.
Figure 3. Chiappeavis, Pengornis and STM-34-1 to scale.

The IVPP hatchling nests in the LRT
between Chiappeavis and Pengornis as derived enantiornithines. Wang et al. nested the IVPP hatchling with Gretcheniao (Wang et al. 2019; Figs. 4–7), a taxon not in the LRT. So, curious about this, I looked up Gretcheniao and added it to the LRT (Fig. 2).

Figure 4. Gretcheniao in situ from Wang et al. 2019 and isolated from the matrix.

Wang et al. were able to understand the crushed post-crania,
of Gretcheniao, but were stymied by the disarticulated skull (Fig. 5) which included an overlooked finger and some neck bones. Their postdentary (pd) is identified here as a parietal. Their second (crescentric-shape) frontal (f) is identified here as a posterior portion of the nasal.

Figure 5. From Wang et al. 2019. The authors were not able to figure out the bones of the skull and did not realize a finger and a few cervicals were in the middle. Compare to figure 6.

A new reconstruction of the skull of Gretcheniao
(Fig. 6) along with the scoring of the post-crania (Fig. 7) nests this taxon within Enantiornithes. In the LRT (Fig. 2) Gretcheniao nests closer to Pengornis (Fig. 3) than to the IVPP hatchling (Fig. 1).

Figure 6. Tracing and reconstruction of the skull of Gretcheniao using DGS. Cervicals are numbered.

Fingers 2 and 3 of Gretcheniao
were quite robust. Finger 1 was tiny. The premaxillary and maxillary teeth were tiny, but the dentary teeth were robust. The tail vertebrae were quite robust and so were their transverse processes.

Figure 7. Elements of Gretcheniao separated more or less into their in vivo positions using Photoshop. Compare to its sister, Pengornis, in figure 3.

Sometimes it is important to have firsthand access to a fossil.
However, in this case firsthand access did not deliver the data presented here (Fig. 6) using Photoshop to colorize and reconstruct published details. Unfortunately, if you follow this method, you too can be shunned from paleontology. Here, as always, academia gets the final vote.

This blogpost was a presentation, a contribution, a demonstration, an experiment.
You are free to accept it or not, but it would be best if you tested it, like a good scientist. Use every taxon and tool available. Don’t leave the description and tracing of a fossil half-finished after skilled preparators have spent months laboriously exposing every sliver.

References
Wang M, Stidham TA, Li Z, Xu X and Zhou Z 2021. Cretaceous bird with dinosaur skull sheds light on avian cranial evolution. Nature Communications. https://doi.org/10.1038/s41467-021-24147-z

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