Temporal range: Paleocene - Pleistocene,1 62–1.8Ma
|Reconstructed skeleton of Titanis walleri, Florida Museum of Natural History|
Phorusrhacids, colloquially known as terror birds, were a clade of large carnivorous flightless birds that were the largest species of apex predators in South America during the Cenozoic, 62–2 million years (Ma) ago.3
They were roughly 1–3 metres (3.3–9.8 ft) tall. Their closest modern-day relatives are believed to be the 80 cm-tall seriemas. Titanis walleri, one of the larger species, is known from Texas and Florida in North America. This makes the phorusrhacids the only known example of large South American predators migrating north during the Great American Interchange (which occurred after the volcanic Isthmus of Panama land bridge rose ca. 3 Ma ago). It was once believed that T. walleri only became extinct around the time of the arrival of humans in North America,4 but subsequent datings of Titanis fossils have failed to provide evidence for their survival more recently than 1.8 Ma ago.5 However, there exist additional findings that date from 450,000 years ago3 and 17,000 years ago,6 that suggest that at least some terror birds survived until the late Pleistocene in Uruguay.
Kelenken guillermoi from Middle Miocene some 15 million years ago, discovered in Patagonia in 2006, represents the largest bird skull yet found. The fossil has been described as being a 71 cm (28 in), nearly intact skull. The beak is roughly 46 cm (18 in) long and curves in a hook shape that resembles an eagle's beak. Most species described as phorusrhacid birds were smaller, 60–90 cm (2.0–3.0 ft) tall, but the new fossil belongs to a bird that probably stood about 3 m (9.8 ft) tall. Scientists theorize that the large terror birds were extremely nimble and quick runners able to reach speeds of 48 km/h (30 mph).8
The etymology of the name Phorusrhacidae is based on the type genus Phorusrhacos. When first described by Florentino Ameghino in 1887, the etymology of Phorusrhacos was not given. Current thinking is that the name is derived from a combination of the Greek words "phoros", which means bearer or bearing, and "rhacos", which translates to wrinkles, scars or rents.9 Researchers have compared Phorusrhacidae with the living families of Cariamidae and Sagittaridae, but their differences in body mass are too drastic, and thus, one cannot depend on these living families for answers.
The members of Phorusrhacidae was very fast and agile. It possessed a vicious beak, a powerful neck and sharp talons. However, even with these attributes, the terror birds usually preyed on smaller prey that could be eaten with less of a struggle. This is due to the fact that the terror birds lacked a strong jaw. Due to the beaks proportions, the jaw could not generate a great deal of force. Although occasionally these birds would attack large prey, it would do so using its beak purely as a spear with quick precise attacks. Then, it would use its feet to hold the prey down and finish it off.10 Although terror birds had a weak beak, its bones were tightly fused together, making them more resilient to force from the front to back direction.
The Terror Bird is believed to be carnivorous rather than herbivorous in its eating behavior. The strong downwards curve from the tip of this beak suggests it ripped the flesh from the body of other animals. Many current bird species with this feature are carnivorous. CT scans performed on the skull of a Terror Bird reveal that the species would not have been able to shake its prey side to side, but rather exert a lot of downward force.11 Its skull shows that it can handle that form of stress the best. This downward force allowed the Terror Bird to shatter bones more easily, stunning its prey and making it easier to swallow whole. Researches would like to think that the Terror Birds closest relative, the Seriema birds, acts very much like a Terror Bird would have; picking up the prey and throwing them down then picking at them. If the prey was too large to swallow whole, the curved tip of the beak allowed the bird to pick at the prey and rip apart flesh, all using its very strong neck structure. They may have also used their claws to tear apart carcasses as well as helping them tear flesh.12
Based on Claudia P. Tambussi, Ricardo de Mendoza, Federico J. Degrange, and Mariana B. Picasso’s work, the Terror Bird's neck can be divided into three main regions (region 1, region 2, and region 3). In the higher regions of the neck, the Terror bird has bifurcate neural spines (BNS) while it has high neural spines in its lower regions. This suggests that the Terror Bird had a highly flexible and developed neck allowing it to carry its heavy head and strike with terrifying speed and power. Although the Terror Bird externally looks like it has a short neck, its flexible skeletal neck structure proves that it can expand farther beyond the expected reach and intimidate it's prey using its height, allowing it to strike more easily. Once stretched out into its full length in preparation for a downward strike, its developed neck muscles and heavy head can produce enough momentum and power to cause fatal damage to the Terror Bird’s prey.13
From 27 million years to 2.5 million years ago, there was an increase in the Terror Bird population size in South America, suggesting that in that time frame it flourished as an apex predator in the savannah environment. However as the Panamanian Land Bridge emerged, 2.5 million years ago, carnivorous dogs and cats from North America were able to cross into South America, causing an increase of competition. Due to the growth of competition, the population of Terror Birds gradually decreased. This suggests that competition with other predators is a major influence to Phorusrhacidae extinction.14 Some researchers believe that the Phorusrhacidae started to go extinct at the beginning of the Pleistocene 2.5 million years ago. South America was also home to a Sebecidae, Madtsoiidae and Sparassodonta, all of which were large carnivores as well that shared similar eating habits to the Phorusrhacidae.15 This meant even more competition for the Terror Bird. This competition drove the Terror bird out of South American and eventually to extinction.
These birds have been in the past thought to have high beaks, round orbits, and vaulted braincases 16 though there was never enough empirical evidence that could support this. However, new fossils have been discovered in Cormollo, Argentina. These skulls reveal that the terror bird has a triangular dorsal view, a rostrum that is hooked and more than half the length of the actual skull, and a more compact caudal portion. The external nares and antorbital fenestras (areas found in the nose) were found to be more square than triangular. These all contribute to a skull that is more rectangular in view rather than triangular.17 The structure of the fossils also suggest that these birds may have been more swift than originally thought.17
A skull from a smaller subspecies of this bird was found recently as well. With this fossil, it was found that the internal structure of the beak is hollow and reinforced with thin-walled trabeculaa. There is also an absence of both zona flexoria palatina and zona flexoria arcus jugalis which are key features that relate to the evolution of cranial akinesis. This discovery of the skull allows for the establishment of primary osteological homologies which are useful in comparative anatomy, functional morphology, and phylogenetic studies.18
- Subfamily Brontornithinae — gigantic species, standing over 2.3 metres (7.5 ft) high. Placement in Phorusrhacidae and/or monophyly disputed.
- Subfamily Phorusrhacinae — giant species 3.2 metres (10 ft) high, but somewhat slender and decidedly more nimble than the Brontornithinae
- Subfamily Patagornithinae — intermediate sized and very nimble species, standing around 1.7 metres (5.6 ft) high
- Subfamily Psilopterinae — small species, standing 70–100 centimetres (2.3–3.3 ft) high
- Subfamily Mesembriornithinae — medium-sized species, standing between 1.2–1.5 metres (3.9–4.9 ft) high
- Genus Mesembriornis (Late Miocene - Late Pliocene)
Alvarenga and Höfling did not include the Ameghinornithidae from Europe in the phorusrhacoids; these have meanwhile turned out to be more basal members of Cariamae.21 Though traditionally considered as members of the Gruiformes, based on both morphological and genetic studies (the latter being based on the seriema22) that they may belong to a separate group of birds (the Cariamae) and their closest living relatives, according to the last nuclear studies, are a clade conformed by Falconidae, Psittaciformes and Passeriformes23
- GeoWhen Database - Gelasian December 2007, from Internet archive
- Ameghino, F (1889). "Contribuición al conocimiento de los mamíferos fósiles de la República Argentina". Actas Academia Nacional Ciencias de Córdoba (in Spanish) 6: 1–1028.
- Blanco, R. E.; Jones, W. W. (2005). "Terror birds on the run: a mechanical model to estimate its maximum running speed". Proceedings of the Royal Society B 272 (1574): 1769–1773. doi:10.1098/rspb.2005.3133.
- Baskin, J. A. (1995). "The giant flightless bird Titanis walleri (Aves: Phorusrhacidae) from the Pleistocene coastal plain of South Texas". Journal of Vertebrate Paleontology 15 (4): 842–844. doi:10.1080/02724634.1995.10011266.
- MacFadden, Bruce J.; Labs-Hochstein, Joann; Hulbert, Richard C.; Baskin, Jon A. (2007). "Revised age of the late Neogene terror bird (Titanis) in North America during the Great American Interchange" (PDF). Geology 35 (2): 123–126. doi:10.1130/G23186A.1.
- Herculano Alvarenga, Washington Jones, and Andrés Rinderknecht (2010). The youngest record of phorusrhacid birds (Aves, Phorusrhacidae) from the late Pleistocene of Uruguay. Neues Jahrbuch für Geologie and Paläont. Abh., 256: 229–234; Stuttgart.
- Mourer-Chauviré, C. et al. (2011) A Phororhacoid bird from the Eocene of Africa. Naturwissenschaften doi:10.1007/s00114-011-0829-5
- Bertelli, Sara; Chiappe, Luis M; Tambussi, Claudia (2007). "A New Phorusrhacid (Aves: Cariamae) from the Middle Miocene of Patagonia, Argentina". Journal of Vertebrate Paleontology 27 (2): 409–419. doi:10.1671/0272-4634(2007)27[409:ANPACF]2.0.CO;2.
- Ben Creisler, "Phorusrhacos “wrinkle bearer (jaw)”: Etymology and Meaning", Dinosaur Mailing List, 26 June 2012 http://dml.cmnh.org/2012Jun/msg00306.html
- Stephen Wroe, et al. "Mechanical Analysis Of Feeding Behavior In The Extinct "Terror Bird' Andalgalornis steulleti (Gruiformes: Phorusrhacidae)." Plos ONE 5.8 (2010): 1-7. Academic Search Premier. Web. 25 Oct. 2013.
- "Ancient “terror Bird” Used Powerful Beak to Jab like an Agile Boxer." OHIO: Research. Ohio Office of Research Communications, 18 Aug. 2010. Web. 24 Oct. 2013. <http://www.ohio.edu/research/communications/terrorbirds.cfm>.
- "Terror Birds of the Phorusrhacidae." Terror Birds of the Phorusrhacidae. Prehistoric Wildlife, n.d. Web. 23 Oct. 2013. <http://www.prehistoric-wildlife.com/articles/terror-birds-of-the-phorusrhacidae.html>.
- Tambussi CP, de Mendoza R, Degrange FJ, Picasso MB. 2013. “Flexibility along the Neck of the Neogene Terror Bird Andalgalornis steulleti (Aves Phorusrhacidae)”. PLOS ONE 7
- Marshall, Larry G. "The Terror Birds of South America." Scientific American Special Edition. N.p., n.d. Web. 24 Oct. 2013. <http://usuarios.geofisica.unam.mx/cecilia/cursos/TerrorBirds-Marshall94.pdf>.
- Prevosti, Francisco; Forasiepi, Analía; Zimicz, Natalia. "The Evolution Of The Cenozoic Terrestrial Mammalian Predator Guild In South America: Competition Or Replacement?." 20.1 (n.d.): 3-22. Web. 25 Oct. 2013.
- Chiappe, Luis M.Bertelli, Sara. "Palaeontology: Skull Morphology Of Giant Terror Birds." Nature 443.7114 (2006): 929. MasterFILE Elite. Web. 24 Oct. 2013.
- Chiappe, Luis M.Bertelli, Sara. "Palaeontology: Skull Morphology Of Giant Terror Birds." Nature 443.7114 (2006): 929. MasterFILE Elite. Web. 24 Oct. 2013
- Federico J. Degrange & Claudia P. Tambussi (2011) Re-examination of Psilopterus lemoinei (Aves, Phorusrhacidae), a late early Miocene little terror bird from Patagonia (Argentina), Journal of Vertebrate Paleontology, 31:5, 1080-1092, DOI: 10.1080/02724634.2011.595466
- Alvarenga, Herculano M.F.; Höfling, Elizabeth (2003). "Systematic revision of the Phorusrhacidae (Aves: Ralliformes)". Papéis Avulsos de Zoologia 43 (4): 55–91. doi:10.1590/S0031-10492003000400001.
- Cenizo, Marcos M. "Review Of The Putative Phorusrhacidae From The Cretaceous And Paleogene Of Antarctica: New Records Of Ratites And Pelagornithid Birds." Polish Polar Research 33.3 (2012): 239-258. Academic Search Premier. Web. 24 Oct. 2013.
- Mayr, Gerald (2005-04-15). "Old World phorusrhacids (Aves, Phorusrhacidae): a new look at Strigogyps ("Aenigmavis") sapea (Peters 1987)" (abstract). PaleoBios 25 (1): 11–16. Retrieved 2008-07-04.
- Hackett, Shannon J.; et al. (2008-06-27). "A Phylogenomic Study of Birds Reveals Their Evolutionary History". Science 320 (5884): 1763–1768. doi:10.1126/science.1157704. PMID 18583609. Retrieved 2008-10-18.
- Alexander Suh et al. (2011-08-23). "Mesozoic retroposons reveal parrots as the closest living relatives of passerine birds". Nature Communications 2 (8). doi:10.1038/ncomms1448. PMC 3265382. PMID 21863010.
- Lemonick, Michael D. "How Prehistoric Terror Birds Killed Their Prey." TIME.com. Time, 20 Aug. 2010. Web. 27 Oct. 2013.
|Wikimedia Commons has media related to Phorusrhacidae.|
- Hooper Museum
- Terror Birds: Bigger and Faster (Science)
- Darren Naish: Tetrapod Zoology: "terror birds"
- Darren Naish: Tetrapod Zoology: "Raven, the claw-handed bird, last of the phorusrhacids" includes links to other articles on phorusrhacids