Phorusrhacidae

{{Short description|Extinct family of flightless birds}} {{Redirect|Terror Bird|the studio album|Terrorbird}} {{Automatic taxobox | fossil_range = Middle Eocene – Late Pleistocene<ref name=oldest/><ref name=Eschatornis>{{Cite journal|last1=Machado |first1=V. H. M. |last2=de Vasconcelos |first2=M. F.|last3=Santos |first3=L. V. |last4=Dutra |first4=L. P. |last5=Cartelle |first5=C. |last6=Câmara |first6=B. G. O. |last7=Dantas |first7=M. A. T. |last8=Degrange |first8=F. J. |title=A new terror bird (Cariamiformes, Phorusrhacidae) from the Late Pleistocene of Brazil: insights into the last representatives of the family |year=2026 |journal=Papers in Palaeontology |volume=12 |issue=2 |article-number=e70080 |doi=10.1002/spp2.70080 }}</ref> ~{{Fossil range|43|0.025|earliest=Ypresian}}{{Detailed fossil range|Cenozoic|43|0.025|earliest=Ypresian}} Possible Early Eocene records | image = Skeleton of Titanis at the Florida Museum of Natural History.jpg | image_upright = 1.1 | image_caption = Reconstructed skeleton of ''Titanis walleri'', Florida Museum of Natural History | parent_authority = Ameghino, 1889 | taxon = Phorusrhacidae | authority = Ameghino, 1889<ref name=Ameghino1889>{{cite journal |last=Ameghino |first=F |year=1889 |title=Contribuición al conocimiento de los mamíferos fósiles de la República Argentina |journal=Actas Academia Nacional Ciencias de Córdoba |volume=6 |pages=1–1028 | language = es |trans-title= Contribution to the knowledge of fossil mammals in the Argentine Republic}}</ref> | type_species = {{extinct}}''Phorusrhacos longissimus'' | type_species_authority = Ameghino, 1887 | subdivision_ranks = Subgroups | subdivision = * {{extinct}}''Brontornis''? * {{extinct}}''Patagorhacos'' * {{extinct}}'''Psilopterinae''' Dolgopol de Saez, 1927 ** {{extinct}}''Eschatornis'' ** {{extinct}}''Procariama'' ** {{extinct}}''Psilopterus'' * {{extinct}}'''Mesembriornithinae''' Kraglievich, 1932 ** {{extinct}}''Llallawavis'' ** {{extinct}}''Mesembriornis'' *{{extinct}}'''Patagornithinae''' Mercerat, 1897 ** {{extinct}}''Andalgalornis'' ** {{extinct}}''Andrewsornis'' ** {{extinct}}''Patagornis'' *{{extinct}}'''Phorusrhacinae''' Ameghino, 1889 ** {{extinct}}''Devincenzia'' ** {{extinct}}''Kelenken'' ** {{extinct}}''Phorusrhacos'' ** {{extinct}}''Titanis'' *{{extinct}}'''Physornithinae''' Agnolin, 2007 ** {{extinct}}''Paraphysornis'' ** {{extinct}}''Physornis'' | synonyms = {{collapsible list|bullets = true |title=Family synonymy |Pelecyornidae Ameghino, 1891 |Brontornithidae Moreno & Mercerat, 1891 |Darwinornithidae Moreno & Mercerat, 1891 |Stereornithidae Moreno & Mercerat, 1891 |Patagornithidae Mercerat, 1897 |Hermosiornidae Rovereto, 1914 |Psilopteridae Dolgopol de Saez, 1927 |Devincenziidae Kraglievich, 1932 |Mesembriorniidae Kraglievich, 1932 }} }}

'''Phorusrhacids''', colloquially known as '''terror birds''', are an extinct family of large carnivorous, mostly flightless birds{{efn|It has been suggested that psilopterines like ''Psilopterus'' may have been able to fly briefly in a clumsy manner, primarily to reach the treetops for nesting and protection, on the basis of body mass estimates and hindlimb proportions being similar to those of certain birds like ''Psophia'' and ''Otis'' which often walk but are able to run and fly.<ref>{{cite journal|author1=Degrange, F.J.|year=2015|title=Hind limb morphometry of terror birds (Aves, Cariamiformes, Phorusrhacidae): functional implications for substrate preferences and locomotor lifestyle|journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh|volume=106|issue=4|pages=257–276|doi=10.1017/S1755691016000256|bibcode=2015EESTR.106..257D |hdl=11336/44728|hdl-access=free}}</ref><ref name=oldest>{{Cite journal|last1=Acosta Hospitaleche |first1=C. |last2=Jones |first2=W. |year=2024 |title=Insights on the oldest terror bird (Aves, Phorusrhacidae) from the Eocene of Argentina |journal=Historical Biology: An International Journal of Paleobiology |volume=37 |issue=2 |pages=391–399 |doi=10.1080/08912963.2024.2304592 |s2cid=267475903 }}</ref>}} that were among the largest apex predators in South America during the Cenozoic era. Their definitive fossil records range from the Middle Eocene to the Late Pleistocene around {{Ma|43|0.025}},<ref name=oldest/><ref name=Eschatornis/> though some specimens suggest that they were present since the Early Eocene.

They ranged in height from {{convert|1|to|3|m|ft|abbr=on|sigfig=1}}. One of the largest specimens from the Early Pleistocene of Uruguay, possibly belonging to ''Devincenzia'', would have weighed up to {{convert|350|kg|lb}}.<ref name=Dev>{{cite journal |last=Alvarenga |first=H. M. F. |author2=Höfling, E. |year=2003 |title=Systematic revision of the Phorusrhacidae (Aves: Ralliformes) |journal=Papéis Avulsos de Zoologia |volume=43 |issue=4 |pages=55–91 |doi=10.1590/S0031-10492003000400001 |doi-access=free}}</ref><ref>{{cite journal |last1=Blanco |first1=Rudemar Ernesto |last2=Jones |first2=Washington W |date=2005 |title=Terror birds on the run: a mechanical model to estimate its maximum running speed |url=https://www.researchgate.net/publication/7664536 |journal=Proceedings of the Royal Society B: Biological Sciences |volume=272 |issue=1574 |pages=1769–1773 |doi=10.1098/rspb.2005.3133 |pmc=1559870 |pmid=16096087}}</ref> Their closest modern-day relatives are believed to be the {{convert|80|cm|in|adj=mid|-tall}} seriemas. ''Titanis walleri'', one of the larger species, is known from Texas and Florida in North America. This makes the phorusrhacids one of a few large South American predator to migrate north in the Great American Interchange (the main pulse of the interchange began about 2.6 Ma ago; ''Titanis'' at 5 Ma was an early northward migrant).<ref name = "Woodburne2010">{{cite journal|last1=Woodburne|first1=M. O.|title=The Great American Biotic Interchange: Dispersals, Tectonics, Climate, Sea Level and Holding Pens|journal=Journal of Mammalian Evolution|volume= 17|issue=4|date= 2010-07-14|pages= 245–264|doi= 10.1007/s10914-010-9144-8|pmid=21125025|pmc=2987556}}</ref>

It was once believed that ''T. walleri'' became extinct in North America around the time of the arrival of humans,<ref name="baskin1995">{{Cite journal | doi = 10.1080/02724634.1995.10011266 | last1 = Baskin | first1 = J. A. | year = 1995 | title = The giant flightless bird ''Titanis walleri'' (Aves: Phorusrhacidae) from the Pleistocene coastal plain of South Texas | journal = Journal of Vertebrate Paleontology | volume = 15 | issue = 4| pages = 842–844 | bibcode = 1995JVPal..15..842B }}</ref> but subsequent datings of ''Titanis'' fossils provided no evidence for their survival after 1.8 Ma.<ref name="mcfaddenetal2007">{{cite journal | last1= MacFadden | pages= 123–126 | first1= Bruce J. | last2= Labs-Hochstein | first2= Joann | last3= Hulbert | first3= Richard C. | last4= Baskin | first4= Jon A. | year= 2007 | title= Revised age of the late Neogene terror bird (''Titanis'') in North America during the Great American Interchange | volume= 35 | doi= 10.1130/G23186A.1 | journal= Geology | issue= 2 | bibcode= 2007Geo....35..123M | s2cid= 67762754 }}</ref> The latest known definitive phorusrhachid is ''Eschatornis'' from the Late Pleistocene of Brazil, dated to approximately 25,326-25,733 calibrated (cal.) years Before Present.<ref name=Eschatornis/>

Phorusrhacids may have even made their way into Africa and Europe, if the genus ''Lavocatavis'' from Algeria and ''Eleutherornis'' from France and Switzerland are included.<ref>{{cite journal | author1 = Mourer-Chauviré, C. | author2 = Tabuce, R. | author3 = Mahboubi, M'hammed | author4 = Adaci, Mohammed | author5 = Bensalah, Mustapha | year = 2011 | title = A Phororhacoid bird from the Eocene of Africa | journal = Naturwissenschaften | volume = 98| issue = 10| pages = 815–823| doi = 10.1007/s00114-011-0829-5 | pmid = 21874523 | bibcode = 2011NW.....98..815M | s2cid = 19805809 }}</ref><ref name="Eleutherornis"/> However, the taxonomic placement of both taxa within phorusrhacids is considered highly questionable, and their remains are too fragmentary to be included in phylogenetic analyses.<ref name=Mayr2017/><ref name=Mayr2022/><ref name=LGO24/> Possible specimens have also been discovered from the La Meseta Formation of Seymour Island, Antarctica, suggesting that this group had a wider geographical range in the Paleogene.<ref>{{Cite journal |last1=Acosta Hospitaleche |first1=Carolina |last2=Jones |first2=Washington |date=2024 |title=Were terror birds the apex continental predators of Antarctica? New findings in the early Eocene of Seymour Island |url=https://palaeo-electronica.org/content/2024/5162-eocene-cariamiformes-from-antarctica |journal=Palaeontologia Electronica |volume=27 |issue=1 |pages=1–31 |doi=10.26879/1340|doi-access=free }}</ref>

The closely related bathornithids occupied a similar ecological niche in North America across the Eocene to Early Miocene; some, like ''Paracrax'', were similar in size to the largest phorusrhacids.<ref name="Benton2015">{{cite book|first1=R. C.|last1= Benton|first2=D. O. Jr.|last2= Terry|first3= E.|last3= Evanoff|first4=H. G.|last4= McDonald|title= The White River Badlands: Geology and Paleontology|url= https://books.google.com/books?id=ZcFtCQAAQBAJ&pg=PA95|date=25 May 2015|publisher= Indiana University Press|isbn=978-0-253-01608-9|page= 95}}</ref><ref name = "Cracraft1968">{{cite journal | last= Cracraft | first= J. | title= A review of the Bathornithidae (Aves, Gruiformes), with remarks on the relationships of the suborder Cariamae | journal= American Museum Novitates | issue= 2326 | pages= 1–46 | date= 1968 | hdl= 2246/2536 }}</ref> At least one analysis recovers ''Bathornis'' as sister taxa to phorusrhacids, on the basis of shared features in the jaws and coracoid,<ref>{{ cite book|first1=Federico L. |last1=Agnolin|year=2009|title=Sistemática y Filogenia de las Aves Fororracoideas (Gruiformes, Cariamae)|publisher=Fundación de Historia Natural Felix de Azara|pages=1–79|language=es|trans-title= Systematics and Phylogeny of Phororrhacoid Birds (Gruiformes, Cariamae)}}</ref> though this has been seriously contested, as these might have evolved independently for the same carnivorous, flightless lifestyle.<ref name= "Mayr2013">{{cite journal|last1= Mayr|first1= G.|last2= Noriega|first2= J.|title=A well-preserved partial skeleton of the poorly known early Miocene seriema ''Noriegavis santacrucensis'' (Aves, Cariamidae)|journal= Acta Palaeontologica Polonica|year= 2013|doi= 10.4202/app.00011.2013|doi-access= free|hdl= 11336/41730|hdl-access= free}}</ref>

== Description == [[File:Phorusrhacidae size comparison.png|thumb|left|300px|Size comparison of some phorusrhacids, including ''Kelenken'', ''Devincenzia'', ''Phorusrhacos'', and ''Titanis'']] The neck can be divided into three main regions. In the higher regions of the neck, the phorusrhacid has bifurcate neural spines (BNS), while it has high neural spines in its lower regions. This suggests that the phorusrhacid had a highly flexible and developed neck allowing it to carry its heavy head and strike with terrifying speed and power. Although the phorusrhacid externally looks like it has a short neck, its flexible skeletal neck structure proves that it could expand farther beyond the expected reach and intimidate its 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 could produce enough momentum and power to cause fatal damage to the terror bird's prey.<ref>{{cite journal | last1 = Tambussi | first1 = CP | last2 = de Mendoza | first2 = R | last3 = Degrange | first3 = FJ | last4 = Picasso | first4 = MB. | year = 2013 | title = Flexibility along the Neck of the Neogene Terror Bird ''Andalgalornis steulleti'' (Aves Phorusrhacidae) | journal = PLOS ONE | volume = 7 | issue = 5| article-number = e37701| doi=10.1371/journal.pone.0037701 | pmid=22662194 | pmc=3360764| bibcode = 2012PLoSO...737701T | doi-access = free }}</ref>

''Kelenken guillermoi'', from the Langhian stage of the Miocene epoch, some 15 million years ago, discovered in the Collón Curá Formation in Patagonia in 2006, represents the largest bird skull yet found. The fossil has been described as being a {{convert|71|cm|adj=on}}, nearly intact skull. The beak is roughly {{convert|46|cm|abbr=on}} long and curves in a hook shape that resembles an eagle's beak. Most species described as phorusrhacid birds were smaller, {{convert|60|-|90|cm|ft|abbr=on}} tall, but the new fossil belongs to a bird that probably stood about {{convert|3|m|ft|abbr=on}} tall. Scientists theorize that the large terror birds were extremely nimble and quick runners, able to reach speeds of {{convert|48|km/h|abbr=on}}.<ref>{{cite journal |last=Bertelli |first=Sara |author2=Chiappe, Luis M |author3=Tambussi, Claudia |year=2007 |title=A New Phorusrhacid (Aves: Cariamae) from the Middle Miocene of Patagonia, Argentina |journal=Journal of Vertebrate Paleontology |volume=27 |issue=2 |pages=409–419 |doi=10.1671/0272-4634(2007)27[409:ANPACF]2.0.CO;2 |s2cid=85693135 }}</ref> Examination of phorusrhacid habitats also indicates that phorusrhacids may have presented intense competition to predatory metatherian sparassodonts such as borhyaenids and thylacosmilids, causing the mammalian predators to choose forested habitats to avoid the more successful and aggressive avian predators on the open plains.<ref name="Antón 2013 61">{{cite book|last=Antón|first=Mauricio|title=Sabertooth|date=2013|publisher=University of Indiana Press|location=Bloomington, Indiana|isbn=978-0-253-01042-1|page=61}}</ref> thumb|Phorusrhacinae skulls compared The feet of the phorusrhacids had four toes, the first of which, known as the hallux, was reduced and did not touch the ground, while the others, corresponding to the second, third and fourth toes, were kept on the ground. Analysis of the resistance of the toes based on biomechanical models of curved beams, in particular of the second toe and its nail claw, indicate that it was modified into a "sickle claw" and was relatively uniform in various species and said claw would be relatively curved and large, which implies the need to keep it elevated to avoid wear or breakage due to contact with the ground, which would be achieved with a well-developed extensor tubercle and soft tissue pads on the fingers. The second toe, which was shorter and had fewer phalanges, also had more resistance and would make it easier to hold the claw off the ground and retain prey, a compromise with its predatory function and movement on the run, as occurs with modern seriemas, although to a lesser degree of specialization than dromaeosaurid dinosaurs.<ref name = Jones2010>{{cite thesis|last1=Jones|first1=Washington W.|year=2010|url=https://www.colibri.udelar.edu.uy/jspui/bitstream/20.500.12008/4112/1/uy24-14537.pdf|title=Nuevos aportes sobre la paleobiología de los fororrácidos (Aves: Phorusrhacidae) basados en el análisis de estructuras biológicas|publisher=Universidad de la República - Facultad de Ciencias|place=Uruguay|lang=es|trans-title=New contributions on the paleobiology of phororrhacids (Aves: Phorusrhacidae) based on the analysis of biological structures|degree=PhD|archive-date=2021-07-14|access-date=2021-03-15|archive-url=https://web.archive.org/web/20210714074816/https://www.colibri.udelar.edu.uy/jspui/bitstream/20.500.12008/4112/1/uy24-14537.pdf|url-status=dead}}</ref> This is further supported by footprints from the Late Miocene of the Río Negro Formation, showcasing a trackway made by a mid-to-large sized terror bird with functionally didactyl footprints, the inner toe with the sickle claw raised mostly off the ground akin to their Mesozoic counterparts.<ref>{{cite journal |last1=Melchor |first1=R |last2=Feola |first2=S |date=September 2023 |title=First terror bird footprints reveal functionally didactyl posture |journal=Nature |volume=13 |issue= 1|page=16474 |doi=10.1038/s41598-023-43771-x |pmid=37777554 |pmc=10542783 |bibcode=2023NatSR..1316474M }}</ref>

=== Skull structure === alt=Phorusrhacid skulls|left|thumb|260x260px|Comparison of different phorusrhacid skulls In the past, these birds were thought to have high beaks, round orbits, and vaulted braincases<ref name="Chiappe, Luis M 2006"/> though there was never enough empirical evidence to support this. However, new fossils have been discovered in Comallo, 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.<ref name="Chiappe, Luis M 2006">{{cite journal | last1 = Chiappe | first1 = Luis M.Bertelli | last2 = Sara | year = 2006 | title = Palaeontology: Skull Morphology Of Giant Terror Birds | journal = Nature | volume = 443 | issue = 7114| page = 929 | doi=10.1038/443929a | pmid=17066027| bibcode = 2006Natur.443..929C | s2cid = 4381103 | doi-access = free }}</ref> The structure of the fossils also suggest that these birds may have been swifter than originally thought.<ref name="Chiappe, Luis M 2006"/>

A skull of ''Psilopterus'' shows the internal structure of the beak was hollow and reinforced with thin-walled trabeculae. 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. The discovery of this skull allows for the establishment of primary osteological homologies, which are useful in comparative anatomy, functional morphology, and phylogenetic studies.<ref>{{cite journal | last1 = Degrange | first1 = Federico J. | last2 = Tambussi | first2 = Claudia P. | year = 2011 | title = Re-examination of ''Psilopterus lemoinei'' (Aves, Phorusrhacidae), a late early Miocene little terror bird from Patagonia (Argentina) | journal = Journal of Vertebrate Paleontology | volume = 31 | issue = 5| pages = 1080–1092 | doi = 10.1080/02724634.2011.595466 | bibcode = 2011JVPal..31.1080D | s2cid = 86790415 }}</ref>

== Palaeobiology == [[File:Andalgalornis jconway.png|thumb|left|Restoration of ''Andalgalornis'']] All phorusrhacids possessed a large hooked beak and a relatively large skull. The bones of the beak were tightly fused together, making the beak more resilient to force from the front to back direction, thus suggesting that it could cause a great amount of harm through pecking, but earlier studies indicated relatively weak bite force quotients. This has led some to argue phorusrachids were poorly suited to tackle larger prey due to them being unable to effectively inflict damage without repeated blows, forcing them to rely largely on relatively tiny prey like small rodents;<ref>{{cite journal | last1 = Wroe | first1 = Stephen |display-authors=etal | year = 2010 | title = Mechanical Analysis Of Feeding Behavior In The Extinct "Terror Bird' ''Andalgalornis steulleti'' (Gruiformes: Phorusrhacidae) | doi = 10.1371/journal.pone.0011856 | pmid = 20805872 | pmc = 2923598 |doi-access=free |journal = PLOS ONE | volume = 5 | issue = 8| pages = 1–7 | bibcode = 2010PLoSO...511856D }}</ref> however, similar cranial and cervical adaptations combining relatively weak bite forces with resistance to vertical and front-to-back stresses also exist in machaidorontine felids, other sabre-toothed mammalian carnivores, and various allosauroid non-avian theropods, animals generally considered predators of larger herbivores,<ref>{{cite journal | last1=Melchionna | first1=Marina | last2=Profico | first2=Antonio | last3=Castiglione | first3=Silvia | last4=Serio | first4=Carmela | last5=Mondanaro | first5=Alessandro | last6=Modafferi | first6=Maria | last7=Tamagnini | first7=Davide | last8=Maiorano | first8=Luigi | last9=Raia | first9=Pasquale | last10=Witmer | first10=Lawrence M. | last11=Wroe | first11=Stephen | last12=Sansalone | first12=Gabriele | title=A method for mapping morphological convergence on three-dimensional digital models: The case of the mammalian sabre-tooth | journal=Palaeontology | date=2021 | volume=64 | issue=4 | pages=573–584 | doi=10.1111/pala.12542 | bibcode=2021Palgy..64..573M | url=https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12542 | hdl=10261/241519 | hdl-access=free }}</ref><ref>{{cite journal | last1=Snively | first1=Eric | last2=Cotton | first2=John R. | last3=Ridgely | first3=Ryan | last4=Witmer | first4=Lawrence M. | title=Multibody dynamics model of head and neck function in Allosaurus (Dinosauria, Theropoda) | journal=Palaeontologia Electronica | date=2013 | volume=16 | issue=2 | page=338 | doi=10.26879/338 | bibcode=2013PalEl..16..338S | url=https://palaeo-electronica.org/content/2013/389-allosaurus-feeding | doi-access=free }}</ref> and later studies have found phorusrhacids to have had far greater bite forces than assumed previously.<ref>{{cite thesis | last1=Degrange | first1=Federico Javier | title=Morfología del cráneo y complejo apendicular posterior de aves fororracoideas: Implicancias en la dieta y modo de vida | date=2012 | publisher=Universidad Nacional de La Plata | doi=10.35537/10915/83640 | url=http://sedici.unlp.edu.ar/handle/10915/83640 }}</ref> Both of these factors have led to larger phorusrhacids being once again viewed as predators of larger mammals in most recent research, while small phorusrhacids with much less robust skulls were likely small-prey specialists.<ref>https://www.researchgate.net/publication/348614159_A_Revision_of_Skull_Morphology_In_Phorusrhacidae_Aves_Cariamiformes</ref><ref>https://pmc.ncbi.nlm.nih.gov/articles/PMC11040249/</ref>

[[File:Holotype trackway of Rionegrina pozosaladensis.png|thumb|right|Only known phorusrhacid trackway, named ''Rionegrina'', which confirms that they held their second toe off the ground like seriemas and dromaeosaurs]] Some phorusrhacids like ''Andalgalornis'', while very fast runners in a straight line, were poor at tight turns at speed, which contradicts the idea of phorusrhacids being agile predators of small prey and indicates a greater focus on larger prey.<ref>{{cite conference |last1=King |first1=Logan |last2=Barrick |first2=Reese |title=Semicircular canal shape within Aves and non-avian Theropoda: Utilizing geometric morphometrics to correlate life history with canal cross-sectional shape |date=October 2016 |conference=Society of Vertebrate Paleontology 76th Annual Meeting At: Salt Lake City, Utah, United States}}</ref>

=== Diet === All phorusrhacids are thought to have been carnivorous. The strong downwards curve from the tip of this beak suggests that it ripped the flesh from the body of other animals; many extant bird species with this feature are carnivorous. CT scans performed on the skull of a phorusrhacid reveal that the species would not have been able to shake its prey side to side, but rather exert significant downward force.<ref>{{cite web | title=Ancient "terror bird" used powerful beak to jab like an agile boxer | website=OHIO: Research | date=Aug 18, 2010 | url=https://www.ohio.edu/research/communications/terrorbirds.cfm | archive-url=https://web.archive.org/web/20170516195018/https://www.ohio.edu/research/communications/terrorbirds.cfm | archive-date=2017-05-16 }}</ref>

Florentino Ameghino claimed in a letter to Édouard Trouessart that he had specimens from Argentina of "petrified masses preserving skeletons of large rodents, Interatheriidae [small notoungulates] and even Proterotheriidae [deer-sized litopterns], with all their bones crushed and corroded, piled on with no apparent order and forming a nearly spherical mass with the skull in the center" that resembled giant owl pellets, suggesting that phorusrhacids may have swallowed their prey whole and regurgitated the indigestible parts similar to owls.<ref>{{cite book |last1=Ameghino |first1=Florentino |title=Obras completas y correspondencia cientifica de Florentino Ameghino |date=1936 |publisher=Taller de Impresiones Oficiales |volume=21|editor-first1=A.J.|editor-last1=Torcelli|location=La Plata|page=573}}</ref><ref name="AngstBuffetaut2017">{{cite book |last1= Angst|first1= D.|last2= Buffetaut |first2= E.|title= Palaeobiology of giant flightless birds |date= 16 November 2017 |url= https://books.google.com/books?id=aU4ADQAAQBAJ&q=fossilized%20pellets |publisher= Elsevier Science |location= Oxford |isbn=978-1-78548-136-9 |pages= 157–158 |oclc= 1012400051}}</ref> However, Ameghino never formally described these specimens and they have not yet been relocated, making it difficult to determine if they are phorusrhacid pellets.<ref name="AngstBuffetaut2017"/> Fossilized pellets from northwestern Argentina have also been suggested to pertain to small phorusrhacids like ''Procariama''.<ref name="Nasif2009">{{cite journal |last1=Nasif |first1=Norma L. |last2=Esteban |first2=Graciela I. |last3=Ortiz |first3=Pablo E. |title=Novedoso hallazgo de egagrópilas en el Mioceno tardío, Formación Andalhuala, provincia de Catamarca, Argentina |journal=Serie Correlación Geológica |date=2009 |volume=25 |issue=105–114}}</ref>

== Classification == 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 "rhakos", which translates to ''wrinkles'', ''scars'' or ''rents''.<ref>{{cite mailing list| title=Phorusrhacos "wrinkle bearer (jaw)": Etymology and Meaning | mailing-list=usc.edu dinosaur |first=Ben |last=Creisler | date=2012-06-26 | url=http://dml.cmnh.org/2012Jun/msg00306.html | archive-url=https://web.archive.org/web/20160304022804/http://dml.cmnh.org/2012Jun/msg00306.html | archive-date=2016-03-04 }}</ref> Researchers have compared Phorusrhacidae with the living families of Cariamidae and Sagittariidae, but their differences in body mass are too drastic and, thus, one cannot overly depend on these living families for answers.

During the early Cenozoic, after the extinction of the non-bird dinosaurs, mammals underwent an evolutionary diversification, and some bird groups around the world developed a tendency towards gigantism; this included the Gastornithidae, the Dromornithidae, the Palaeognathae, and the Phorusrhacidae.<ref>{{Cite journal |date=6 February 2017 |title=Flights of Fancy in Avian Evolution |url=https://www.americanscientist.org/article/flights-of-fancy-in-avian-evolution |access-date=11 May 2023 |journal=American Scientist |language=en |doi=10.1511/2014.106.36 |last1=Ksepka |first1=Daniel |volume=102 |page=36 |url-access=subscription }}</ref> Phorusrhacids are an extinct group within Cariamiformes, the only living members of which are the two species of seriemas in the family Cariamidae. While they are the most taxon-rich group within Cariamiformes, the interrelationships between phorusrhacids are unclear due to the incompleteness of their remains.<ref name="skull morphology3">{{cite journal |last1=Degrange |first1=Federico J. |date=2020 |title=A revision of skull morphology in Phorusrhacidae (Aves, Cariamiformes) |url=https://www.researchgate.net/publication/348614159 |journal=Journal of Vertebrate Paleontology |volume=40 |issue=6 |article-number=e1848855 |doi=10.1080/02724634.2020.1848855 |bibcode=2020JVPal..40E8855D |s2cid=234119602}}</ref> A lineage of related predatory birds, the bathornithids, occupied North America prior to the arrival of phorusrhacids, living from the Eocene to Miocene and filled a similar niche to phorusrhacids.<ref>{{cite journal |last=Cracraft |first=J. |year=1968 |title=A review of the Bathornithidae (Aves, Gruiformes), with remarks on the relationships of the suborder Cariamae |journal=American Museum Novitates |issue=2326 |url=https://archive.org/details/reviewbathornit2326crac/reviewbathornit2326crac/}}</ref> Only one genus belongs in the family, ''Bathornis'', according to a 2016 analysis by paleontologist Gerald Mayr, who noted that ''Bathornis'' was more lightly built, with longer limbs proportionally and skulls more akin to those of ''Cariama''.<ref name=":10">{{Cite journal |last=Mayr |first=Gerald |date=2016 |title=Osteology and phylogenetic affinities of the middle Eocene North American Bathornis grallator—one of the best represented, albeit least known Paleogene cariamiform birds (seriemas and allies) |url=https://www.cambridge.org/core/product/identifier/S0022336016000457/type/journal_article |journal=Journal of Paleontology |language=en |volume=90 |issue=2 |pages=357–374 |bibcode=2016JPal...90..357M |doi=10.1017/jpa.2016.45 |issn=0022-3360 |s2cid=88936361|url-access=subscription }}</ref>

[[File:Cariama cristata-seriema-01.jpg|thumb|236x236px|The red-legged seriema, the closest living relative of phorusrhacids]] Phylogenetic analysis of Cariamiformes and their relatives according to Mayr (2016) in his redescription of ''Bathornis'':<ref name=":10" /> A 2024 study finds ''Bathornis'' as closer to seriemas than phorusrhacids were.<ref name=LGO24/>

{{clade|{{clade |label4=Cariamiformes |1=Opisthocomidae |2=''Paracrax'' |3=''Elaphrocnemus'' |4={{clade |1= ''Bathornis'' |2= ''Ameghinornis'' |3= ''Dynamopterus'' |4={{clade |1= ''Cariama'' |2='''Phorusrhacidae''' }}

}} }}|style=font-size:90%;line-height:100%;}}

Following the revision by Alvarenga and Höfling (2003), there are now 5 subfamilies, containing 13 genera and 22 species:<ref name=Alvarengaetal2003>{{cite journal |last1=Alvarenga |first1=Herculano M. F. |last2=Höfling |first2=Elizabeth |year=2003 |title=Systematic revision of the Phorusrhacidae (Aves: Ralliformes) |journal=Papéis Avulsos de Zoologia |volume=43 |issue=4 |pages=55–91 |doi=10.1590/S0031-10492003000400001|doi-access=free }}</ref> These species were the product of adaptive radiation.<ref>{{cite journal | last1 = Cenizo | first1 = Marcos M. | year = 2012 | title = Review of the Putative Phorusrhacidae from the Cretaceous and Paleogene of Antarctica: New Records of Ratites and Pelagornithid Birds| journal = Polish Polar Research | volume = 33 | issue = 3| pages = 239–258  | doi = 10.2478/v10183-012-0014-3 | bibcode = 2012PPolR..33..239C | doi-access = free }}</ref> The following classification is based on LaBarge, Garderner & Organ (2024), and taxa identified as ''incertae sedis'' were all excluded from phylogenetic analysis in their study (except for ''Brontornis''):<ref name=LGO24>{{cite journal |last1=LaBarge |first1=T. W. |last2=Gardner |first2=J. D. |last3=Organ |first3=C. L. |year=2024 |title=The evolution and ecology of gigantism in terror birds (Aves, Phorusrhacidae) |journal=Proceedings of the Royal Society B: Biological Sciences |volume=291 |issue=2021 |at=20240235 |doi=10.1098/rspb.2024.0235 |pmid=38654650 |pmc=11040249}} [https://rs.figshare.com/articles/journal_contribution/S1_Text_from_The_evolution_and_ecology_of_gigantism_in_terror_birds_Aves_Phorusrhacidae_/25546651?backTo=/collections/Supplementary_material_from_The_evolution_and_ecology_of_gigantism_in_terror_birds_Aves_Phorusrhacidae_/7165777 Supplementary information]</ref>

[[File:1064376 - Megafauna - Museu Nacional de História Natural UFRJ - 22 Outubro 2010 - Rio de Janeiro - Brazil.jpg|thumb|Reconstructed skeleton of ''Paraphysornis'' at the Museu Nacional, Rio de Janeiro]] [[File:Skull of Andalgalornis steulleti.png|thumb|upright|CT scan of the skull of P 14357, holotype of ''Andalgalornis ferox'' in the collections of the Field Museum of Natural History]] '''Family Phorusrhacidae''' *'''''Incertae sedis''''' ** Genus ?''Lavocatavis'' – Middle Eocene Glib Zegdou Formation of Algeria (likely more related to a possible paleognath ''Eremopezus''<ref name=Mayr2017>{{cite book|last=Mayr |first=G.|year=2017|chapter=Cariamiforms and Diurnal Birds of Prey|title=Avian Evolution: The Fossil Record of Birds and its Paleobiological Significance|pages=189–204|publisher=Wiley-Blackwell|location=Chichester|isbn=978-1-119-02076-9}}</ref>) ** Genus ?''Patagorhacos'' – Early Miocene Chichinales Formation of Rio Negro Province, Argentina.<ref name=ChichinalesFmbirds>{{Cite journal|author1=Federico L. Agnolin |author2=Pablo Chafrat |name-list-style=amp |year=2015 |title=New fossil bird remains from the Chichinales Formation (Early Miocene) of northern Patagonia, Argentina |journal=Annales de Paléontologie |volume= 101|issue= 2|pages= 87–94|doi=10.1016/j.annpal.2015.02.001 |bibcode=2015AnPal.101...87A }}</ref> ** Genus ?''Paleopsilopterus'' – Lower Eocene (Itaboraian) Itaboraí Formation of Itaboraí, Brazil (identity as a phorusrhacid dubious)<ref name="Eleutherornis"/><ref>{{cite journal | last1 = Alvarenga | first1 = H. M. F. | last2 = Höfling | first2 = E. | year = 2003 | title = Systematic revision of the Phorusrhacidae (Aves: Ralliformes) | url =http://www.scielo.br/pdf/paz/v43n4/17491.pdf | journal = Papéis Avulsos de Zoologia | volume = 43 | issue = 4| pages = 55–91 | doi = 10.1590/s0031-10492003000400001 | doi-access = free }}</ref> ** Genus ?''Brontornis'' – Early to Middle Miocene (Santacrucian–Laventan) Santa Cruz and Monte León Formations, Argentina – gigantic species, standing on average {{convert|8.6|ft|m}} high. Placement in Phorusrhacidae and/or monophyly disputed. ** Genus ?''Eleutherornis'' – Middle Eocene (Bartonian) of Rhône, France and Baselland, Switzerland<ref name= Eleutherornis>{{Cite journal | doi = 10.1371/journal.pone.0080357| title = 'Terror Birds' (Phorusrhacidae) from the Eocene of Europe Imply Trans-Tethys Dispersal| journal = PLOS ONE| volume = 8| issue = 11| article-number = e80357| year = 2013| last1 = Angst | first1 = D. | last2 = Buffetaut | first2 = E. | last3 = Lécuyer | first3 = C. | last4 = Amiot | first4 = R. | pmid=24312212 | pmc=3842325| bibcode = 2013PLoSO...880357A| doi-access = free}}</ref> (a cariamiform, probably more related to ''Strigogyps''<ref name=Mayr2017/><ref name=Mayr2022>{{cite book|last=Mayr |first=G.|year=2022|chapter=Accipitriformes (New World Vultures, Hawks, and Allies), Falconiformes (Falcons), and Cariamiformes (Seriemas and Allies)|title=Paleogene Fossil Birds|series=Fascinating Life Sciences |publisher=Springer Cham|pages=153–176|doi=10.1007/978-3-030-87645-6_8|isbn=978-3-030-87644-9 }}</ref>) * '''Subfamily Physornithinae''' — equivalent to '''Brontornithinae''', if ''Brontornis'' is included within the family ** Genus ''Paraphysornis'' (Late Oligocene to Early Miocene (Deseadan) Tremembé Formation of São Paulo State, Brazil) ** Genus ''Physornis'' (Middle to Late Oligocene (Deseadan) Sarmiento Formation of Santa Cruz Province, Argentina) * '''Subfamily Phorusrhacinae''' — giant species {{convert|8.3|ft|m}} high (''Kelenken'' up to {{convert|9.8|ft|m}} high<ref>{{cite journal | last=Alvarenga | first=Herculano | title=South American and Antarctic Continental Cenozoic Birds — Paleobiogeographic Affinities and Disparities | journal=Ameghiniana | publisher=Asociacion Paleontologica Argentina | volume=51 | issue=3 | year=2014 | issn=0002-7014 | doi=10.5710/amgh.v51i3.2 | page=266| s2cid=126914134 }}</ref>), but somewhat slender and decidedly more nimble than the Brontornithinae ** Genus ''Devincenzia'' – Miocene to Early Pliocene, possibly up to Early Pleistocene<ref>{{cite journal |last1=Tambussi |first1=Claudia |last2=Ubilla |first2=Martín |last3=Perea |first3=Daniel |date=1999 |title=The youngest large carnassial bird (Phorusrhacidae, Phorusrhacinae) from South America (Pliocene-Early Pleistocene of Uruguay) |journal=Journal of Vertebrate Paleontology |volume=19 |issue=2 |pages=404–406 |doi=10.1080/02724634.1999.10011154 |jstor=4524003 |bibcode=1999JVPal..19..404T |issn=0272-4634}}</ref><ref name=Dev/> ** Genus ''Kelenken'' – Middle Miocene (Colloncuran) Collón Curá Formation of Río Negro Province, Argentina; largest known phorusrhacid ** Genus ''Phorusrhacos'' – Early to Middle Miocene (Santacrucian) Santa Cruz Formation of Argentina ** Genus ''Titanis'' – Early Pliocene to Early Pleistocene (Blancan) of Florida, California, and Texas<ref name="mcfaddenetal2007" /><ref>{{cite conference| last1=Chandler | first1=Robert M. | last2=Jefferson | first2=George T. | last3=Lindsay | first3=Lowell | last4=Vescera | first4=Susan P. | title=The Terror Bird, Titanis (Phorusrhacidae) from Pliocene Olla Formation, Anza-Borrego Desert State Park, Southern California |conference=Raising Questions in the central Mojave Desert: The 2013 Desert Symposium Field Guide and Proceedings | date=2013-04-01 |url=http://www.desertsymposium.org/DS_2013_Raising_Questions.pdf |pages=181–183|archive-url=https://web.archive.org/web/20230721104522/http://www.desertsymposium.org/DS_2013_Raising_Questions.pdf|archive-date=2023-07-21 }}</ref> * '''Subfamily Patagornithinae''' — intermediate sized and very nimble species, standing around {{convert|5.4|ft|m}} high ** Genus ''Patagornis'' – Early to Middle Miocene (Santacrucian–Laventan) Santa Cruz Formation of Santa Cruz Province, Argentina – includes ''Morenomerceraria'', ''Palaeociconia'', ''Tolmodus'' ** Genus ''Andrewsornis'' – Middle to Late Oligocene (Deseadan) Agua de la Piedra Formation of southern Argentina ** Genus ''Andalgalornis'' – Late Miocene to Early Pliocene (Huayquerian) Ituzaingó Formation of northwestern Argentina * '''Subfamily Psilopterinae''' — small species, standing {{convert|3.2|ft|m}} high ** Genus ''Eschatornis'' - Late Pleistocene of Brazil ** Genus ''Psilopterus'' – Middle Oligocene (Deseadan) Santa Cruz Formation and Late Miocene (Chasicoan) Arroyo Chasicó Formation of southern and eastern Argentina respectively (Possible Late Pleistocene (Lujanian) records from Uruguay<ref name="Jones2017">{{Cite journal |last1=Jones |first1=W. |last2=Rinderknecht |first2=A. |last3=Alvarenga |first3=H. |last4=Montenegro |first4=F. |last5=Ubilla |first5=M. |year=2017 |title=The last terror birds (Aves, Phorusrhacidae): new evidence from the late Pleistocene of Uruguay |journal=Paläontologische Zeitschrift |volume=92 |issue=2 |pages=365–372 |doi=10.1007/s12542-017-0388-y |s2cid=134344096}}</ref>) ** Genus ''Procariama'' – Late Miocene to Early Pliocene (Huayquerian–Montehermosan) Cerro Azul and Andalhualá Formations of Catamarca Province, Argentina * '''Subfamily Mesembriornithinae''' — medium-sized species, standing {{convert|4.4|ft|m}} high ** Genus ''Mesembriornis'' – Late Miocene to Late Pliocene (Montehermosan) Monte Hermoso Formation of Argentina ** Genus ''Llallawavis'' – Late Pliocene (Chapadmalalan) Playa Los Lobos Allo Formation of northeastern Argentina<ref name=Degrange>{{Cite journal|first1=Federico J. |last1=Degrange |first2=Claudia P. |last2=Tambussi |first3=Matías L. |last3=Taglioretti |first4=Alejandro |last4=Dondas |first5=Fernando |last5=Scaglia |year=2015 |title=A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds |journal=Journal of Vertebrate Paleontology |volume=35 |issue= 2|article-number= e912656|doi=10.1080/02724634.2014.912656 |bibcode=2015JVPal..35E2656D |s2cid=85212917 |hdl=11336/38650 |hdl-access=free }}</ref>

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.<ref name=Mayr2005>{{cite journal |last=Mayr |first=Gerald |date= 2005-04-15 |title=Old World phorusrhacids (Aves, Phorusrhacidae): a new look at ''Strigogyps'' ("''Aenigmavis''") ''sapea'' (Peters 1987) |journal=PaleoBios |volume=25 |issue=1 |pages=11–16 |url=http://www.ucmp.berkeley.edu/science/paleobios/abstracts_21to25.php |access-date=2008-07-04 |format=abstract }}</ref> Though traditionally considered as members of the Gruiformes, based on both morphological and genetic studies (the latter being based on the seriema<ref>{{cite journal | last = Hackett | first = Shannon J. | title = A Phylogenomic Study of Birds Reveals Their Evolutionary History | journal = Science | volume = 320 | issue = 5884 | pages = 1763–1768 | date = 2008-06-27 | doi = 10.1126/science.1157704 | pmid = 18583609| bibcode = 2008Sci...320.1763H | s2cid = 6472805 |display-authors=etal}}</ref>) Cariamiformes may belong to a separate group of birds, Australaves, and their closest living relatives, according to nuclear sequence studies, are a clade consisting of Falconidae, Psittaciformes and Passeriformes.<ref name=Suh>{{cite journal|title=Mesozoic retroposons reveal parrots as the closest living relatives of passerine birds|author=Alexander Suh|journal=Nature Communications|volume=2|date=2011-08-23|issue=8|doi=10.1038/ncomms1448|pmid=21863010|pmc=3265382|display-authors=etal|article-number=443|bibcode=2011NatCo...2..443S}}</ref><ref name = "Jarvis2014">{{Cite journal| doi = 10.1126/science.1253451| pmid = 25504713| url = https://pgl.soe.ucsc.edu/jarvis14.pdf| title = Whole-genome analyses resolve early branches in the tree of life of modern birds| journal = Science| volume = 346| issue = 6215| pages = 1320–1331| date = 2014| last1 = Jarvis| first1 = E. D.| author1-link = Erich Jarvis| last2 = Mirarab| first2 = S.| last3 = Aberer| first3 = A. J.| last4 = Li| first4 = B.| last5 = Houde| first5 = P.| last6 = Li| first6 = C.| last7 = Ho| first7 = S. Y. W.| last8 = Faircloth| first8 = B. C.| last9 = Nabholz| first9 = B.| last10 = Howard| first10 = J. T.| last11 = Suh| first11 = A.| last12 = Weber| first12 = C. C.| last13 = Da Fonseca| first13 = R. R.| last14 = Li| first14 = J.| last15 = Zhang| first15 = F.| last16 = Li| first16 = H.| last17 = Zhou| first17 = L.| last18 = Narula| first18 = N.| last19 = Liu| first19 = L.| last20 = Ganapathy| first20 = G.| last21 = Boussau| first21 = B.| last22 = Bayzid| first22 = M. S.| last23 = Zavidovych| first23 = V.| last24 = Subramanian| first24 = S.| last25 = Gabaldon| first25 = T.| last26 = Capella-Gutierrez| first26 = S.| last27 = Huerta-Cepas| first27 = J.| last28 = Rekepalli| first28 = B.| last29 = Munch| first29 = K.| last30 = Schierup| first30 = M.| display-authors = 6 | pmc = 4405904| bibcode = 2014Sci...346.1320J| hdl = 10072/67425| access-date = 2018-05-27| archive-url = https://web.archive.org/web/20191206033643/https://pgl.soe.ucsc.edu/jarvis14.pdf| archive-date = 2019-12-06}}</ref>

The following cladogram follows the analysis of Degrange and colleagues, 2015:<ref name=Degrange/>

{{clade|style=white-space:nowrap;font-size:85%;line-height:100% |grouplabel1={{clade labels|label1=Physornithinae |top1=93% |label2=Phorusrhacinae |top2=58% |label3=Patagornithinae |top3=78% }} |label1='''Phorusrhacidae''' |1={{clade |label1="psilopterines" |1={{clade |label1=Mesembriornithinae |1={{clade |1=''Mesembriornis incertus'' |2={{clade |1=''Mesembriornis milneedwardsi'' |2={{clade |1=''Llallawavis scagliai'' |2=''Procariama simplex'' }} }} }} |label2=Psilopterinae |2={{clade |label1=''Psilopterus'' |1={{clade |1={{clade |1=''Psilopterus affinis'' |2=''Psilopterus bachmanni'' }} |2={{clade |1=''Psilopterus colzecus'' |2=''Psilopterus lemoinei'' }} }} }} }} |label2=true "terror birds" |2={{clade |1=''Kelenken guillermoi'' |bar1=red |2={{clade |1=''Devincenzia pozzi'' |bar1=red |2={{clade |1=''Titanis walleri'' |bar1=red |2={{clade |2=''Paraphysornis brasiliensis'' |bar2=yellow |1={{clade |1=''Phorusrhacos longissimus'' |bar1=red |2=''Andalgalornis steulleti''|bar2=blue |3=''Andrewsornis abbotti'' |bar3=blue |4=''Patagornis marshi'' |bar4=blue |5=''Physornis fortis'' |bar5=yellow }} }} }} }} }} }} }}

== Extinction == [[File:Procariama.jpg|thumb|Life restoration of ''Procariama'' in paleoenvironment]] During the Miocene and early Pliocene epochs, there was an increase in the phorusrhacid population size in South America, suggesting that, in that time frame, the various species flourished as predators in the savanna environment.

With the emergence of the Isthmus of Panama 2.7 million years ago, carnivorous dogs, bears, and cats from North America were able to cross into South America, increasing competition.<ref name = "GAIpatterns">{{cite journal | last = Webb | first = S. David | title = The Great American Biotic Interchange: Patterns and Processes | journal = Annals of the Missouri Botanical Garden | volume = 93 | issue = 2 | pages = 245–257| date = 23 August 2006| doi = 10.3417/0026-6493(2006)93[245:TGABIP]2.0.CO;2 | s2cid = 198152030 }}</ref> (They had been preceded by procyonids as early as 7.3 million years ago.<ref name = "Woodburne2010"/>) Traditionally, workers assumed that population of phorusrhacids declined thereafter and suggested that competition with newly arrived predators was a major contributor to their extinction.<ref>{{cite journal | last=Marshall | first=Larry G. | title=The Terror Birds of South America | journal=Scientific American | publisher=Springer Science and Business Media LLC | volume=270 | issue=2 | year=1994 | issn=0036-8733 | doi=10.1038/scientificamerican0294-90 | pages=90–95 | bibcode=1994SciAm.270b..90M |url=http://usuarios.geofisica.unam.mx/cecilia/cursos/TerrorBirds-Marshall94.pdf}}</ref> Similar ideas have been considered for sparassodonts and for South America's terrestrial sebecid crocodilians.<ref name = "Gasparini">{{cite journal | last = Gasparini | first = Zulma | title = New Tertiary Sebecosuchia (Crocodylia: Mesosuchia) from Argentina | journal = Journal of Vertebrate Paleontology | volume = 4 | issue = 1 | pages = 85–95 |date=September 1984 | doi = 10.1080/02724634.1984.10011988 | jstor = 4522967| bibcode = 1984JVPal...4...85G }}</ref>

However, the role of competitive displacement in the extinction of South American predator lineages has been questioned in more recent years,<ref>{{cite mailing list |first=Darren |last=Naish |title=Dumb Metatherians vs Evil, Smart Placentals |mailing-list=USC dinosaur |date=30 May 2001 |url=http://dml.cmnh.org/2001May/msg00530.html |archive-url=https://web.archive.org/web/20111120060114/http://dml.cmnh.org/2001May/msg00530.html |archive-date=2011-11-20 }}</ref><ref name=":0">Agnolín, F.L. (2009) ''[https://www.fundacionazara.org.ar/img/libros/sistematica-y-filogenia-de-aves-fororracoideas-ok.pdf Sistemática y Filogenia de las Aves Fororracoideas (Gruiformes, Cariamae)]'' Fundación de Historia Natural Félix de Azara: Buenos Aires, Argentina</ref>, and has largely been discounted. The timing of turnover events and the decline of South American predators do not correlate well with the arrival of large carnivores like canids or sabretooths (although they do correlate well with the earlier-arriving procyonids, which evolved to large body size in South America, but these were omnivorous<ref>{{cite journal | last1=Kraglievich | first1=J.L. | last2=Olazabal | first2=A.G. | title=Los prociónidos extinguidos del género Chapalmalania Ameghino | journal=Revista del Museo Argentino de Ciencias Naturales | publisher=Museo Argentino de Ciencia Naturales | volume=6 | date=1959-01-01 | issn=1514-5158 | pages=1–59 | url=https://www.researchgate.net/publication/284098225 |language=es}}</ref>), with native South American predator lineages (including most phorusrhacids and all sparassodonts and sebecids) dying out well before the arrival of most larger placental carnivores.<ref name="link.springer.com">{{cite journal | last1 = Prevosti | first1 = Francisco J |last2 = Forasiepi | first2 = Analía | last3 = Zimicz | first3 = Natalia | year = 2013| title = The Evolution Of The Cenozoic Terrestrial Mammalian Predator Guild In South America: Competition Or Replacement?| journal = Journal of Mammalian Evolution | volume = 20 | issue = 1| pages = 3–21 | doi=10.1007/s10914-011-9175-9| s2cid = 15751319 | hdl = 11336/2663 | hdl-access = free }}</ref> Bathornithids, which were similar in ecology and are likely close relatives of phorusrhacids, existed entirely within North America during part of the Cenozoic and competed successfully for a time with large carnivorans such as nimravids,<ref name = "Cracraft1968" /> before becoming extinct in the Early Miocene, about 20 million years ago. The phorusrhacid ''Titanis'' expanded northward into southern North America during the Interchange and were able to establish themselves in North America for several million years. During its existence, it coexisted with carnivorans such as borophagines, hyaenids, and machairodonts.<ref name=":17">{{Cite book |last=Dalquest |first=Walter Woelber |url=https://www.biodiversitylibrary.org/bibliography/142927 |title=Vertebrate fossils from the Blanco local fauna of Texas |date=1975 |publisher=Museum, Texas Tech University |location=Lubbock |doi=10.5962/bhl.title.142927 |access-date=15 May 2023 |archive-url=https://web.archive.org/web/20230513124607/https://www.biodiversitylibrary.org/bibliography/142927 |archive-date=13 May 2023 |url-status=live}}</ref><ref name=":0" /> [[File:Paraphysornis brasiliensis (model) Naturhistorisches Museum Wenen 7-06-2023 10-37-20.jpg|thumb|''Paraphysornis brasiliensis'' model at the Natural History Museum Vienna]] Furthermore, this hypothesis heavily relies on the idea that phorusrhacids had physiological and paleontological similarities to insular birds. Despite being an isolated continent, South America was considerably different than islands inhabited by flightless birds. Additionally, island evolution is influenced by the size of the land mass. Paleohistological analysis further refutes competitive replacement, as they found rapid, uninterrupted growth patterns in phoruscrhacids. This contrasts growth patterns of insular birds as they had a more protracted growth rate. This was the result of inhabiting islands or well adapted, stable ecosystems that lacked of strong predation pressure, this made insular birds more vulnerable to competition or predation. Unlike the islands flightless birds inhabited, South America had non-avian terrestrial predators such as sebecids and sparassodonts. The authors concluded that rapid, interrupted growth would’ve made phorusrhacids less vulnerable to competition or predation by carnivorans. This would suggest that the extinction of phorusrhacids was due to environmental conditions.<ref>{{cite journal |last1=Marsà |first1=J. A. G.|last2=Angolín |first2=F. L. |last3=Angst |first3=Delphine |last4=Buffetaut |first4=Eric |title=Paleohistological Analysis of "Terror Birds" (Phorusrhacidae, Brontornithidae): Paleobiological Inferences |journal=Diversity |volume=17 |issue=1 |date=2025 |page=153 |doi=10.3390/d17030153 |doi-access=free|bibcode=2025Diver..17..153M }}</ref>

There were some suggestions that phorusrhacids, like the majority of Pleistocene megafauna, were killed off by human activity such as hunting or habitat change. This idea is no longer considered valid, as improved dating on ''Titanis'' specimens show that the last large phorusrhacids went extinct well over one and a half million years before humans arrived.<ref name="mcfaddenetal2007" /> However, several fossil finds of smaller forms have been described from the late Pleistocene of South America. The most definitive evidence is represented by ''Eschatornis'', known from a partial left tibiotarsus directly dated to 25,326-25,733 cal. years Before Present.<ref name=Eschatornis/> ''Psilopterus'' may have been present until 96,040 ± 6,300 years ago (maximum age obtained from the bottom of the fossil-containing stratum), which would extend the existence of the smaller members of this group of avian predators considerably.<ref name="Jones2017"/> Another unidentified smaller type which may be a possible psilopterine<ref name="Jones2017"/> from the La Paz Local Fauna of Uruguay has also been dated to the late Pleistocene, perhaps 17,620 ± 100 years ago based on radiocarbon analysis using accelerator mass spectrometry (AMS) for the molar enamel samples of a proboscidean from the same site,<ref>{{cite journal|last1= Alvarenga|first1= H.|last2= Jones|first2= W.|last3= Rinderknecht|first3= A.|title= The youngest record of phorusrhacid birds (Aves, Phorusrhacidae) from the late Pleistocene of Uruguay|journal= Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen|volume= 256|issue= 2|year= 2010|pages= 229–234|doi= 10.1127/0077-7749/2010/0052|bibcode= 2010NJGPA.256..229A|url=http://www.museuhistorianatural.com/pesquisa_arquivos/2010/Phorusrh._Pleist.sup.Alvarenga.pdf}}</ref> but the validity of this previous radiocarbon dating has been considered highly questionable due to the enamel's lack of collagen;<ref>{{Cite journal |last1=Corona |first1=Andrea |last2=Perea |first2=Daniel |last3=Toriño |first3=Pablo |last4=Goso |first4=Cesar |year=2012 | title=Taphonomy, sedimentology and chronology of a fossiliferous outcrop from the continental Pleistocene of Uruguay |url=https://www.researchgate.net/publication/274080498 |journal=Revista Mexicana de Ciencias Geológicas |volume=29 |issue=2 |pages=514–525 |via=ResearchGate }}</ref> the tibia of ''Macrauchenia patachonica'' from the same site has been more precisely dated to a mean value of approximately 21,600 ± 1,000 years ago based on gamma spectrometry and radiocarbon dating.<ref name=dating>{{cite journal|first1=A.S.|last1=Cid|first2=R.M.|last2=Anjos|first3=C.B.|last3=Zamboni|first4=R.|last4=Cardoso|first5=M.|last5=Muniz|first6=A.|last6=Corona|first7=D.L.|last7=Valladares|first8=L.|last8=Kovacs|first9=K.|last9=Macario|first10=D.|last10=Perea|first11=C.|last11=Goso|first12=H.|last12=Velasco|year=2014|title=Na, K, Ca, Mg, and U-series in fossil bone and the proposal of a radial diffusion–adsorption model of uranium uptake|journal=Journal of Environmental Radioactivity|volume=136|pages=131–139|doi=10.1016/j.jenvrad.2014.05.018|pmid=24953228 |bibcode=2014JEnvR.136..131C |hdl=11336/5799 |hdl-access=free}}</ref>

== Notes == {{Notelist}}

== References == {{Reflist|2}}

== External links == {{Commons category}} * [https://hoopermuseum.earthsci.carleton.ca/flightless/phorus.htm Hooper Museum] * [https://www.science.org/content/article/terror-birds-bigger-and-faster Terror Birds: Bigger and Faster] (Science) * [http://darrennaish.blogspot.com/2006/10/terror-birds.html Darren Naish: Tetrapod Zoology: "terror birds"] * [https://scienceblogs.com/tetrapodzoology/2008/06/18/raven-the-clawhanded-bird Darren Naish: Tetrapod Zoology: "Raven, the claw-handed bird, last of the phorusrhacids"] includes links to other articles on phorusrhacids * [https://xkcd.com/3069/ xkcd Terror Bird]

Category:Phorusrhacidae Category:Extinct flightless birds Category:Ypresian first appearances Category:Pleistocene extinctions Category:Extinct apex predators Category:Cenozoic birds of South America Category:Taxa named by Florentino Ameghino Category:Prehistoric bird families