SVP abstracts – 15: on the skull of Vegavis, a latest Cretaceous bird from Antarctica

Torres et all 2022 report:
“Fossils representing Cretaceous lineages of extant birds (Aves) are exceedingly rare but are nevertheless crucial to elucidating changes in key anatomical systems across early avian divergences, and importantly, transformations at the crown. Among the earliest known putative crown birds is Vegavis iaai, a diving form from the latest Cretaceous (69.2–68.4 Ma) of Antarctica with controversial phylogenetic affinities.

In the large reptile tree (LRT, 2171 taxa) Vegavis (sans skull, Clark et al 2005, Hospitaleche and Worthy 2021) nested with extant Crypturellus (the cinereous tinamou, native to the Amazon basin, Fig 1) and Early Eocene Pseuodcrypturus. These are all basal paleognaths in the lineage of ostriches, kiwis and emus.

The earliest known crown bird in the LRT is Early Cretaceous Archaeorhynchus and the unnamed LNTU-WLMP-18 specimen. Thereafter paleognaths split from neognaths (all other extant birds and a few fossil taxa).

There is one latest Cretaceous anseriform: Asteriornis. Based on its derived node in the LRT, that means a great deal of undiscovered bird radiation occurred during the Cretaceous, alongside a great deal of undiscovered mammal evolution. That’s why we have giant penguins in the Paleocene.

“Here, we report a new, nearly complete skull of Vegavis that provides new data on its phylogenetic affinities, feeding ecology, and neuroanatomy. The new specimen consists of a mostly complete rostrum, palate, orbital region, neurocranium, and basicranium, as well as much of the mandible. The rostral margin consists exclusively of the premaxilla, with an extremely reduced maxilla not expressed on the lateral aspect of the upper beak, strongly supporting an assignment to the avian crown.

Does that describe the rostral margin of Crypturellus (see Fig 1). It seems to.

“Additionally, Vegavis has a brain shape characteristic of crown birds (i.e., a relatively expanded cerebrum, ventrally-positioned optic lobes, and a low, broad wulst). The new specimen displays the specific bicondylar craniomandibular articulation previously reported in Vegavis and consistent with placement within Galloanserae.

Galloanserae is an invalid genomic clade, combining farm chickens and jungle peacocks with unrelated (in the LRT) water-loving ducks and geese.

“Moreover, morphologies of both the vomer and basipterygoid articulation, as well as the expansive temporal fossa, are more like Anseriformes than Galliformes (landfowl).

More like Anseriformes than Galliformes = more like geese than pheasants. At this point in writing this paragraph I wanted to see and score the specimen, so I Googled “Vegavis skull“, hoping the paper had come out.

A Google search produced an unlabeled fossil bird skull in left and right lateral views. It was similar to the expected morphology (based on the LRT relationship to Crypturellus, Fig 1), but twice the size, just as the skeleton is twice the size (Fig 2).

The link was to Twitter. When I got there, I ran into this blurb:
“This Tweet was deleted by the Tweet author“.

Out of respect for that deletion, I will not re-post the otherwise unidentified photo prior to official publication. The image was publication-quaility with scale bar and abbreviated labels.

I ran a typical DGS tracing on the suspect photo and made comparisons. I can tell you neither the published post-crania of Vegavis nor the unnamed deleted skull belong to an anseriform. Perhaps Torres et al. will note this and not push forward with an anseriform hypothesis invalidated by simply adding taxa.

We looked at Vegavis earlier here, when Hospitaleche and Worthy 2021 promoted considered it a foot-propelled diving bird (Fig 2) despite having tall tinamou proportions (Fig 2).

References
Clarke JA, Tambussi CP, Noriega JI, Erickson GM and Ketcham RA 2005. Definitive fossil evidence for the extant avian radiation in the Cretaceous. Nature 433, 305–308.
Hospitaleche CA and Worthy TH 2021. New data on the Vegavis iaai holotype from the Maastrichian of Antarctica. Cretaceous Research https://www.sciencedirect.com/science/article/abs/pii/S0195667121000653
Torres C et al (7 co-authors) 2022. Nearly complete skull of Latest Cretaceous bird Vegavis iaai provides new insights on feeding ecology and neuroanatomy in early phases of avian crown group diversification. SVP abstracts 2022:345.

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