The origin of giant birds: Gastornis (Diatryma), the giant parrot

Earlier we talked about the giant Gastornis as the sister to the parrot, Ara in the large reptile tree (LRT, 1119 taxa). Traditionally workers considered Gastornis a giant goose. Not sure why… unless they never tested Gastornis with parrots.

But first
let’s take a look at a recent paper on parrot origins, Wright et al. 2008. I came by this study while looking for fossil parrots, especially those without a descending beak tip. I did not find any. The Wright et al. study found an Australasia origin for the clade during the Cretaceous without any close relationships among modern birds.

That last conclusion is, of course, unacceptable and illogical. 
Here’s the problem: Wright’s team chose Falconiformes (Falcons), Columbiformes (pigeons and doves), Cuculiformes (cuckoos), Piciformes (woodpeckers), Coraciiformes (kingfishers), Strigiformes (owls), and Coliiformes (mousebirds) as outgroups because each was considered an ally or sister of parrots at one time or another in recent molecular phylogenetic work.

Therein lies the answer to the problem.
The large reptile tree (LRT, 1119 taxa) based on morphology nests all of these taxa far from parrots, a clade that nests with the hoatzin (Opisthocomus), the sparrow (Passer) and the chicken (Gallus) in order of increasing distance. DNA does not work over large phylogenetic distances ~ especially when sister taxa are excluded from the analysis!!

On a similar note
Bourdon and Cracraft 2011, nested Gastornis deep within the terror birds, which they mistakenly labeled, the Cariamae. I say mistakenly because the seriema, Cariama, is more closely related to flamingoes than to terror birds in the LRT, as reported earlier. This is where a wide gamut study, like the LRT, comes in handy. If Gastornis were truly a terror bird, it would have nested with them in the LRT.

don’t guess, imagine or follow tradition or your professors when choosing your taxon list. Let an overarching study, like the LRT, guide you in your selection.

Now, on to our main topic…

Figure 1. Gastornis (=Diatryma) to scale with Ara the parrot (lower right).

Figure 1. Gastornis (=Diatryma) to scale with Ara the parrot (lower right).

Ara macao (Linneaus 1758; extant ) is the scarlet macaw. Here it nests with the giant Eocene parrot, Gastornis in the LRT. Both are among the few birds that separate the orbit from the temporal fenestrae. In parrots digit 4 (mislabeled above) extends posteriorly along with digit 1. This happens by convergence in several clades, btw.

Figure 3. Skulls of Gastornis, Brontornis and Ara, the scarlet macaw.

Figure 3. Skulls of Gastornis, Brontornis and Ara, the scarlet macaw. Ara is not to scale. Brontornis is another giant parrot known from a mandible, a metatarsus and little else.

Gastornis parisiensis (Hebert 1855, Matthew et al. 1917) is one of several species, including G. (formerly Diatryma) gigantea. Derived from a sister to Opisthocomus, the hoatzin, Gastornis nests as a sister to Ara. Likely an herbivore, Gastornis had vestigial forelinmbs, cursorial hind limbs and redeveloped an upper temporal fenestra with an enlarged postfrontal, postorbital and squamosal, as in parrots. The rostrum is chiefly composed of the premaxilla, as in parrots.

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

Figure 4. Bird giants in the bird subset of the LRT.

Bourdon E and Cracraft J 2011. Gastornis is a terror bird: New insights into the evolution of the cariamae (Aves, Neornithes). Society of Vertebrate Paleontology 71stAnnual Meeting Program and Abstracts, p. 75
Cope ED 1876. 
On a gigantic bird from the Eocene of New Mexico. Proceedings of the Academy of Natural Sciences of Philadelphia 28 (2): 10–11.
Hébert E 1855a. Note sur le tibia du Gastornis pariensis [sic] [Note on the tibia of G. parisiensis]. C. R. Hebd. Acad. Sci. Paris (in French) 40: 579–582.
Hébert E 1855b. Note sur le fémur du Gastornis parisiensis [Note on the femur of G. parisiensis]. C. R. Hebd. Acad. Sci. Paris (in French) 40: 1214–1217.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Matthew WD, Granger W and Stein W 1917. The skeleton of Diatryma, a gigantic bird from the Lower Eocene of Wyoming. Buletin of the American Museum of Natural History, 37(11): 307-354.
Owen R 1843. On the remains of Dinornis, an extinct gigantic struthious bird. Proceedings of the Zoological Society of London: 8–10, 144–146.
Prévost C 1855. Annonce de la découverte d’un oiseau fossile de taille gigantesque, trouvé à la partie inférieure de l’argile plastique des terrains parisiens [Announcement of the discovery of a fossil bird of gigantic size, found in the lower Argile Plastique formation of the Paris region]. C. R. Hebd. Acad. Sci. Paris (in French) 40: 554–557.
Wright TF, et al. (ten co-authors) 2008. A Multilocus Molecular Phylogeny of the Parrots (Psittaciformes): Support for a Gondwanan Origin during the Cretaceous. Molecular Biology and Evolution, 25 (10), 2141-2156 DOI: 10.1093/molbev/msn160.



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