Giant flightless birds: Worthy et al. 2017

Worthy et al. nest several giant flightless birds
with chickens and ducks. In the large reptile tree (LRT, 1094 taxa, subset Fig. 1) none of these giants nest with chickens and ducks. Furthermore, chickens (Gallus) and ducks (Anas) don’t nest with each other in the LRT. They don’t look like each other, so their separation makes sense.

Figure x. Bird giants in the bird subset of the LRT.

Figure 1. Bird giants in the bird subset of the LRT.

From the Worthy et al. abstract:
“The extinct dromornithids, gastornithids and phorusrhacids are among the most spectacular birds to have ever lived, with some giants exceeding 500 kg. The affinities and evolution of these and other related extinct birds remain contentious, with previous phylogenetic analyses being affected by widespread convergence and limited taxon sampling. We recognize a robust new clade (Gastornithiformes) for the giant flightless Dromornithidae (Australia) and Gastornithidae (Eurasia, North America). This clade exhibits parallels to ratite palaeognaths in that flight presumably was lost and giant size attained multiple times South America’s largest bird, Brontornis, is not a galloansere, but a member of Neoaves related to Cariamiformes.”

Figure 2. Brontornis parts compared to Gastornis, a close match both in size and morphology.

Figure 2. Brontornis parts compared to Gastornis, a close match both in size and morphology.

Brontornis bits ‘n pieces
Apparently Brontornis is known from a big metatarsus and a big fused dentary (lower beak), perhaps not enough to nest it in the LRT, but South American terror birds (Cariamiformes according to Worthy et al., a clade not supported here, Fig. 1) have a very narrow beak, whereas Brontornis does not. Here (Fig. 2) the shape and size of Brontornis is quite similar to the giant parrot, Gastornis (formerly Diatryma).

While writing this paragraph
I was drawn to the Wiki Brontornis page, which reports (after describing Brontornis as a giant, flightless terror bird), “Recent work (Agnolin 2007, Buffetaut 2014) ]has cast doubt on the hypothesis that Brontornis is a phorusrhacid. Brontornis may actually represent an anseriform” (traditionally ducks, geese and screamers, but the LRT nests screamers apart). Not sure why the Brontornis/wiki author could not make a scientific statement with more confidence. After all, there is only one answer. The other is false.

From the Worthy et al. introductiion
“Landfowl (Galliformes) and waterfowl (Anseriformes) form a diverse and important clade (Galloanseres) that is sister to Neoaves (all other extant non-palaeognath birds).” This is what Prum 2015 recovered using DNA, but it is not what the LRT recovered (Figs. 1–4) using morphology and extinct taxa.

Worthy et al. also report, 
“These giant flightless Galloanseres show striking morphological convergence with flightless palaeognaths (ratites), especially the large extinct pypyornithidae (elephant birds; Madagascar) and Dinornithiformes (moa; New Zealand).” The LRT recovers elephant birds (Aepyornis) with ratites (Struthio) and moas (Dinornis) between toucans (Pteroglossus) and parrots (Ara, Figs. 1, 3-5). So Worthy et al. appear to be basing their hypotheses on very shaky ground.

While we’re on the subject of birds
here are a few clade divisions recovered by the LRT.

Figure 2. Bird clades, basal divisions.

Figure 3. Bird clades, basal divisions. Where are all the Late Cretaceous birds? They are waiting to be discovered. Please note: Aepyornis now nests with Struthio.

Figure 2. Bird predators and omnivores compared to plant/nectar eaters.

Figure 4. Bird predators and omnivores compared to plant/nectar eaters. Please note: Aepyornis now nests with Struthio.

Figure 4. Most basal birds have a premaxilla about the length of the maxilla. That changes in these two basal clades.

Figure 5. Most basal birds have a premaxilla about the length of the maxilla. That changes in these two basal clades. I know I’m pulling a Larry Martin here, but after the phylogenetic analysis, not before. This trait stood out as a readily visible major division at a node that has remained difficult to establish for prior analyses. Please note: Aepyornis now nests with Struthio.

The basal radiation of extant birds
has been clouded in mystery in prior studies. Here, with fewer taxa (Figs 1-5), the radiation is quite clear and it probably occurred deep into the Early Cretaceous with a large gap sprinkled with taxa until the Tertiary and then greatly expanded with living taxa.

References
Agnolin F 2007. Brontornis burmeisteri Moreno & Mercerat, un Anseriformes (Aves) gigante del Mioceno Medio de Patagonia, Argentina. Revista del Museo Argentino de Ciencias Naturales, n.s.9, 15-25.
Buffetaut E 2014. Tertiary ground birds from Patagonia (Argentina) in the Tournouër collection of the Muséum National d’Histoire Naturelle, Paris. Bulletin de la Société Géologique de France. 185(3):207–214.
Worthy TH, Degrange FJ, Handley WD and Lee MSY 2017. The evolution of giant flightless birds and novel phylogenetic relationships for extinct fowl (Aves, Galloanseres). Royal Society Open Science 4: 170975. http://dx.doi.org/10.1098/rsos.170975

tetrapodzoology/terror-birds

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