The origin of giant birds: Phorusrhacos, the giant secretary bird

Figure 1. Phorushacids to scale. The extant Sagittarius is in color at lower right.

Figure 1. Phorushacids to scale. The extant Sagittarius is in color at lower right. Considering how closely Sagittarius looks like these taxa, one might be surprised to hear that Cariama (Fig. 4) is widely considered the extant relative. Cariama is not the sister in the LRT.

Traditionally
the seriema (genus: Cariama; Fig. 4) has been allied to the ‘terror’ birds, the phorusrhacids (Fig. 1), but it does not have the elevated external naris and deep beak found in the secretary bird (genus: Sagittarius, Figs. 1, 3). Sagittarius also has a more robust set of cervicals. Heretically, in the large reptile tree (LRT, 1120 taxa), the secretary bird of Africa is closer to phorusrhacids of South America.

Figure 3. Skull of Phorusrhacos, a giant terror bird.

Figure 3. Skull of Phorusrhacos, a giant terror bird in three views.

The terror-bird clade is represented in the fossil record
all the way back to the mid-Paleocene (Paleopsilopterus, no skull material known).

Figure 2. Sagittarius (secretary bird) and Cariama (seriema). While clearly related, these two nest at the base of two different major bird clades.

Figure 4. Sagittarius (secretary bird) and Cariama (seriema). While clearly related, these two nest at the base of two different major bird clades. Sagittarius is allied with terror birds. Cariama is allied with flamingo.

Sagittarius serpentarius (Miller 1779) The extant secretary bird is a chiefly terrestrial bird with long legs capable of short flights. It is a sister to Llallawavis, an ancient ‘terror bird.’

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

Figure 5. Bird giants in the bird subset of the LRT.

References
Alvarenga, HMF and Höfling E 2003. Systematic revision of the Phorusrhacidae (Aves: Ralliformes). Papéis Avulsos de Zoologia 43(4): 55-91.
Statius Müller PL 1776. Des Ritters Carl von Linné Königlich Schwedischen Leibarztes &c. &c. vollständigen Natursystems Supplements- und Register-Band über alle sechs Theile oder Classen des Thierreichs. Mit einer ausführlichen Erklärung. Nebst drey Kupfertafeln.Nürnberg. (Raspe).

wiki/Phorusrhacos
wiki/Sagittarius

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