Antarctic Vegavis: a foot-propelled diving bird?

We’ll start today’s post with a question with an obvious, but overlooked answer.
Did you ever wonder why the most primitive extant birds, those that survived the K-T extinction event and gave rise to all other birds, from hummingbirds to petrels, are all poor flyers (megapodes) and non-flyers (ratites)?

Hospitaleche and Worthy 2021 bring us
new data on the holotype of Vegavis (Fig. 1) by freeing the bones we’ve seen before (Clark et al. 2005) of this latest Maastrichtian bird from Antarctica.

We looked at Vegavis
earlier, before the elements were freed from the stone matrix that entombed them for the last 66 million years. Based on that data, the large reptile tree (LRT, 1819+ taxa) nested Vegavis as the proximal outgroup to crown birds (all extant birds and their fossil relatives) basal to the extant Kiwi, Apteryx, and the more similar Early Eocene Pseudocryptus (Fig. 1).

Hospitaleche and Worthy report
“A basal position, excluded from the Neornithes, was also proposed by McLachlan et al. (December 2017), three months later than the LRT and twelve years after Clarke et al. 2005 did the same.

From the Hospitaleche and Worthy abstract:
“Vegavis iaai has key importance as the most complete of the few neornithine birds known from the Cretaceous, yet its phylogenetic relationships remain controversial. The skeleton reveals a mix of features supporting enhanced diving ability for the bird. We make three-dimensional scans and high-quality images of all bones in the holotype available for further comparisons.”

The drawing of Vegavis
provided by Hospitaleche and Worthy 2021 (Fig. 1) does indeed look like a diving bird, but it does not look like the bones of Vegavis (Fig. 1). Vegavis bones resemble those found in Pseudocrypturus (Fig. 1). That’s why everyone nests Vegavis just outside the clade of crown birds where Apteryx and Pseudocrypturus are the birds just inside the clade of crown birds.

If anyone knows why
the Hospitaleche and Worthy 2021 drawing of Vegavis does not match the Vegavis bones, please drop a line and let us know. I suspect it’s because Hospitaleche and Worthy 2021 were looking at tiny details and ignoring the overall proportions. There is no mention of Archaeornithura or Pseudocrypturus in Clarke et al. 2005 or Hospitaleche and Worthy 2021 who both considered Vegavis a type of goose. In the LRT, it is much more primitive.

Getting back to that opening question about primitive barely volant birds…
Apparently all the good-flying birds of the Mesozoic became extinct along with the classic dinosaurs at the K-T boundary. Good flyers evolved again and re-radiated early in the Paleocene. The refugium for these poor-flying birds had to be somewhere on the planet left less scarred by the calamity that devastated the rest of the planet. Could that place be the most remote continent on the planet, Antarctica? The phylogenetic nesting and geological placement of Vegavis makes a case for this hypothesis.

But, wait, there’s more to consider.
Mesozoic toothed birds are phylogenetic descendants of Vegavis in the LRT. That means Vegavis had its genesis in the Early Cretaceous and its last stand at the K-T boundary. As we learned earlier, Paleocene birds are known from every continent except Antarctica and they were a diverse lot, including pre-penguins. That means there might have bird refuges everywhere around the globe, unless the K-T bird radiation out of Antarctica was extremely swift and varied. A lot came happen in one million or one hundred thousand years. More Mesozoic crown bird fossils, if they are out there, will resolve this issue.

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

wiki/Vegavis

This is the first blogpost produced after WordPress changed its format for the worse. Now it is no longer possible to access previous illustrations by indexing text content. Only the last few dozen figures, the one most recently uploaded, are shown on a page. Hopefully WordPress will revert this problem to the earlier format, the one that worked so well for the last ten years.