Secretary birds (genus: Sagittarius) are small, extant terror birds

Phorusrhachids, the giant terror birds of South America,
are the closest relatives of the secretary bird of Africa, Sagittarius, in the large reptile tree (LRT, 1869+ taxa). The similar, but more distantly related seriema (genus: Cariama) of South America is closer to flamingos (Phoenicopterus) than to terror birds, despite the geographic proximity and tradition.


Secretary birds must have appeared on the planet
prior to the rifting of South America from Africa in the Early Cretaceous, 100 mya (Fig. 1). Afterwards there was a growing ocean between secretary birds and terror birds, as in toucans and hornbills.

Figure 4. South America and Africa during the Albian, 100 mya. This is when toucans and hornbills must have separated.
Figure 1. South America and Africa during the Albian, 100 mya. This is when toucans and hornbills must have separated.

This secretary bird video and its narration is wonderful.
It sheds light on how early birds and bird-like theropds lived and preyed on a menu of Late Cretaceous and Tertiary snakes and mammals. Fascinating stuff, especially when the filmmakers propose a new use for feathers.

Figure 3. Skull of Phorusrhacos, a giant terror bird in three views.
Figure 2. Skull of Phorusrhacos, a giant terror bird in three views.
Figure 1. Phorusrhacos to scale with Dinornis, Struthio and Homo.
Figure 3. Phorusrhacos to scale with Dinornis, Struthio and Homo.
Figure 5. Cariama compared to Sagittarius. The former is closer to flamingos. The latter is closer to terror birds.
Figure 4 Cariama compared to Sagittarius. The former is closer to flamingos. The latter is closer to terror birds.
Figure 2. Sagittarius (secretary bird) and Cariama (seriema). While clearly related, these two nest at the base of two different major bird clades.
Figure 5. Sagittarius (secretary bird) and Cariama (seriema). While clearly related, these two nest at the base of two different major bird clades.

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