Sagittarius is not only a constellation of the zodiac,
it’s a genus.
Figure 1. Phorusrhacos to scale with Dinornis, Struthio and Homo.
The giant Phorusrhachids or terror birds
were some of the largest predators of the Cenozoic. Essentially they were theropod dinosaurs retooled with hooked beaks and short tails. Not only do they have living relatives in the seriema, genus Caraima, they nest close to the base of some of the sweet songbirds and budgies we’ve all let sit on our fingers! Imagine the gene pool!!
Figure 2. Sagittarius (secretary bird) and Cariama (seriema). While clearly related, these two nest at the base of two different major bird clades.
(genus Cariama cristatus, Linneaus 1766) is an extant long-legged snake and small prey predator of the high grasslands from Argentina. Despite their relatively short wings, Cariama is capable of flight, though rare and usually as last resort escape from predators.
Figure x. Cariama cristatus, the seriema in several views.
(genus: Sagittarius serpentarius) (Miller 1779) is extant hook-beaked bird of prey that cruises tall grasses in search of small prey including snakes. The name likely comes from the Arabic, saqr-et-tair, or ‘hunter bird’. Standing 1m tall on extended legs, this otherwise eagle-like bird has relatively short wings.
Figure 1. The secretary bird, Sagittarius serpentaris and those extraordinary long legs and feet. About four feet tall.
In the large reptile tree (LRT, 1054 taxa) Sagittarius is a sister to Cariama and both are close to the terror birds. At present there are very few birds in the LRT.
Figure 2. Llallawavis skeleton, one of the most complete phorusrhacids known
Llallawavis scagliai (“ya-ya-WA-vis”; Degrange et al. 2015; Pliocene, 3.5 mya; 1.2m tall) is a member of the Phorushacidae or terror birds. Llallawavis is the most complete fossil yet found from this clade. Distinct from Sagittarius and Cariama, Llallawavis had a larger skull and vestigial wings.
Figure 3. Llallawavis skull in 3 views with DGS identifying bones, many of which are fused to one another. Image from DeGrange et al. with DGS added. Note DeGrange et al. labeled bones but did not delineate sutures. That needs to be done. Here the palatine is shown to be restricted to a small area below the maxilla and the rest is the pterygoid. Note the expansion of the maxilla in the reinforcement of this killing beak.
Skull bones are fused
in many birds including Llallawavis. Even so, DGS is used to tease out former sutures to greater or lesser success. This is something that needs to be done by authors with firsthand access to original material.
The pelvis of Llallawavis was longer, especially posterior to the acetabulum, and the legs not so long as in extant grassland birds (above). The posterior torso was deeper and pedal digit 3 was longer.
Figure 4. Phorusrhacus skull in three views. The normally gracile bones of a bird skull are here reinforced on this giant predator that killed with its beak.
(Ameghino, 1887; Miocene, 2.5m tall)
Hacket et al. 2008 report
both Cariama and Sagittarius nest at the base of adjoining clades. So they are relatively closely related themselves and likely developed short wings and long legs in parallel. I say this because all related taxa have shorter legs and larger wings.
Cariama nests at the base of falcons + parrots + Passeriformes (perching birds). Sagittarius nests at the base hawks and eagles, + owls + mouse birds + trogons + hornbills + woodpeckers + kingfishers and kin.
The overall pattern in both clades
is from vicious terrestrial and aerial predator to smaller seed-eating songbird on the one hand and smaller insect- and fish-eater on the other.
Alvarenga HMF and Hófling E 2003. Systematic revision of the Phorusrhacidae (Aves: Ralliformes) Papéis Avulsos de Zoologia 43(4):55-91.
Ameghino F 1887. Enumeración sistemática de las espécies de mamíferos fósiles coleccionados por Carlos Ameghino en los terrenos Eocenos de la Patagonia austral y depositados en el Museo de La Plata. Boletim Museo La Plata, 1:1-26.
Degrange, FJ et al. 2015. A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds. Journal of Vertebrate Paleontology. 35 (2): e912656. doi:10.1080/02724634.2014.912656.
Hackett SJ et al. 2008. A Phylogenomic Study of Birds Reveals Their Evolutionary History. Science 320, 1763–1768.
Linneaus C 1766. Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. Holmiae. (Laurentii Salvii).: 1-532.
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. (Rapse).