Phorusrhacids, colloquially known as terror birds, are an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of large

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

, mostly

flightless bird Flightless birds are birds that cannot Bird flight, fly, as they have, through evolution, lost the ability to. There are over 60 extant species, including the well-known ratites (ostriches, emus, cassowary, cassowaries, Rhea (bird), rheas, an ...

s that were among the largest

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

s in

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

during the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

era. Their definitive fossil records range from the

Middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...

to the

Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...

around , though some specimens suggest that they were present since the

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

. They ranged in height from . One of the largest specimens from the

Early Pleistocene The Early Pleistocene is an unofficial epoch (geology), sub-epoch in the international geologic timescale in chronostratigraphy, representing the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently esti ...

Uruguay Uruguay, officially the Oriental Republic of Uruguay, is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast, while bordering the Río de la Plata to the south and the A ...

, possibly belonging to '' Devincenzia'', would have weighed up to . Their closest modern-day relatives are believed to be the seriemas. '' Titanis walleri'', one of the larger species, is known from

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

and

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. This makes the phorusrhacids the only known large South American predator to migrate north in the

Great American Interchange The Great American Biotic Interchange (commonly abbreviated as GABI), also known as the Great American Interchange and the Great American Faunal Interchange, was an important late Cenozoic paleozoogeographic biotic interchange event in which land ...

that followed the formation of the

Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...

land bridge In biogeography, a land bridge is an isthmus or wider land connection between otherwise separate areas, over which animals and plants are able to cross and colonize new lands. A land bridge can be created by marine regression, in which sea le ...

(the main pulse of the interchange began about 2.6 Ma ago; ''Titanis'' at 5 Ma was an early northward migrant). It was once believed that ''T. walleri'' became extinct in North America around the time of the arrival of humans, but subsequent datings of ''Titanis'' fossils provided no evidence for their survival after 1.8 Ma. However, reports from

of new findings of phorusrachids such as a specimen of '' Psilopterus'' dating to 96,040 ± 6,300 years ago would imply that phorusrhacids survived in South America until the

late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...

. Phorusrhacids may have even made their way into

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

and

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, if the genus '' Lavocatavis'' from

Algeria Algeria, officially the People's Democratic Republic of Algeria, is a country in the Maghreb region of North Africa. It is bordered to Algeria–Tunisia border, the northeast by Tunisia; to Algeria–Libya border, the east by Libya; to Alger ...

and '' Eleutherornis'' from

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

and

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

are included. However, the taxonomic placement of both taxa within phorusrhacids are considered highly questionable, and their remains are too fragmentary to be included in phylogenetic analyses. Possible specimens have also been discovered from the La Meseta Formation of Seymour Island,

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

, suggesting that this group had a wider geographical range in the

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

. The closely related bathornithids occupied a similar

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources an ...

across the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

Early Miocene The Early Miocene (also known as Lower Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages: the Aquitanian age, Aquitanian and Burdigalian stages. The sub-epoch lasted from 23.03 ± 0.05 annum, Ma to ...

; some, like '' Paracrax'', were similar in size to the largest phorusrhacids. At least one analysis recovers '' Bathornis'' as sister taxa to phorusrhacids, on the basis of shared features in the jaws and

coracoid A coracoid is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is present as part of the scapula, but this is n ...

, though this has been seriously contested, as these might have evolved independently for the same carnivorous, flightless lifestyle.

Description

The neck can be divided into three main regions. In the higher regions of the neck, the phorusrhacid has bifurcate

neural spines Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...

(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. '' Kelenken guillermoi'', from the

Langhian The Langhian is, in the ICS geologic timescale, an age or stage in the middle Miocene Epoch/Series. It spans the time between 15.97 ± 0.05 Ma and 13.65 ± 0.05 Ma (million years ago) during the Middle Miocene.GeoWhen (2007) The Langhian was ...

stage of the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

epoch, some 15 million years ago, discovered in the

Collón Curá Formation The Collón Curá Formation () is a Middle Miocene fossiliferous geological formation of the southern Neuquén Basin in northwestern Patagonia and the western Cañadón Asfalto Basin of central Patagonia, Argentina. The formation crops out fro ...

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

in 2006, represents the largest bird

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

yet found. The fossil has been described as being a , nearly intact skull. The beak is roughly long and curves in a hook shape that resembles an eagle's beak. Most species described as phorusrhacid birds were smaller, tall, but the new fossil belongs to a bird that probably stood about tall. Scientists theorize that the large terror birds were extremely nimble and quick runners, able to reach speeds of . 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. Phorusrhacinae skulls

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 Dromaeosauridae () is a family (biology), family of feathered coelurosaurian Theropoda, theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous period (geology), Period. The name Drom ...

dinosaurs. This is further supported by footprints from the

Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

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.

Skull structure

In the past, these birds were thought to have high beaks, round

orbits In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an physical body, object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an satellite, artificia ...

, and vaulted braincases 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 Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

that is hooked and more than half the length of the actual skull, and a more compact caudal portion. The external nares and antorbital

fenestra A fenestra (fenestration; : fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biology, biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomy, ...

s (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. The structure of the fossils also suggest that these birds may have been swifter than originally thought. A skull from a smaller subspecies of this bird was also found recently. With this fossil, it was found that the internal structure of the beak is 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.

Palaeobiology

Most phorusrhacids were very fast and agile. All members possessed a large hooked beak and a relatively large skull. Phorusrhacids are assumed to have preyed on smaller animals that could both be killed more safely and be swallowed whole. This is due to the fact that with the phorusrhacids' beak proportions, the jaw could not generate a great deal of bite force with which to kill the prey. However, 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. If larger prey were to have been hunted, it would require multiple precise pecks. Despite a lack of sharp talons, struggling prey could also have been restrained by foot. Holotype trackway of Rionegrina pozosaladensis

Holotype trackway of Rionegrina pozosaladensis

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.

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.

Florentino Ameghino Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino; September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especial ...

claimed in a letter to Édouard Trouessart that he had specimens from

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

of "petrified masses preserving skeletons of large rodents, Interatheriidae mall notoungulates">notoungulates.html" ;"title="mall notoungulates">mall notoungulatesand 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 Pellet (ornithology), owl pellets, suggesting that phorusrhacids may have swallowed their prey whole and regurgitated the indigestible parts similar to owls. However, Ameghino never formally described these specimens and they have not yet been relocated, making it difficult to determine if they are phorusrhacid pellets. Fossilized pellets from northwestern

have also been suggested to pertain to small phorusrhacids like '' Procariama''.

Classification

The etymology of the name Phorusrhacidae is based on the type genus '' Phorusrhacos''. When first described by

in 1887, the etymology of ''Phorusrhacos'' was not given. Current thinking is that the name is derived from a combination of the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

words "phoros", which means ''bearer'' or ''bearing'', and "rhakos", which translates to ''wrinkles'', ''scars'' or ''rents''. 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

, after the extinction of the non-bird dinosaurs,

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

underwent an evolutionary diversification, and some bird groups around the world developed a tendency towards

gigantism Gigantism (, ''gígas'', "wiktionary:giant, giant", plural γίγαντες, ''gígantes''), also known as giantism, is a condition characterized by excessive growth and height significantly above average height, average. In humans, this conditi ...

; this included the Gastornithidae, the Dromornithidae, the

Palaeognathae Palaeognathae (; ) is an infraclass of birds, called paleognaths or palaeognaths, within the class Aves of the clade Archosauria. It is one of the two extant taxon, extant infraclasses of birds, the other being Neognathae, both of which form Neo ...

, and the Phorusrhacidae. 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. 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. 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''. Cariama cristata-seriema-01

Phylogenetic analysis of Cariamiformes and their relatives according to Mayr (2016) in his redescription of ''Bathornis'': A 2024 study finds ''Bathornis'' as closer to seriemas than phorusrhacids were. Following the revision by Alvarenga and Höfling (2003), there are now 5 subfamilies, containing 14

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

and 18

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

: These species were the product of adaptive radiation. 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''):Supplementary information
/ref> Family Phorusrhacidae *''

Incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' ** Genus ?'' Lavocatavis'' – Middle Eocene Glib Zegdou Formation of Algeria (likely more related to a possible paleognath '' Eremopezus'') ** Genus ?'' Patagorhacos'' – Early Miocene Chichinales Formation of Rio Negro Province, Argentina. ** Genus ?'' Paleopsilopterus'' – Lower Eocene ( Itaboraian) Itaboraí Formation of Itaboraí, Brazil (identity as a phorusrhacid dubious) ** Genus ?'' Brontornis'' – Early to Middle Miocene ( Santacrucian–

Laventan The Laventan () age is a period of geologic time (13.8 to 11.8 Ma) within the Middle Miocene epoch of the Neogene, used more specifically within the SALMA classification in South America. It follows the Colloncuran and precedes the Mayoan age. ...

) Santa Cruz and Monte León Formations, Argentina – gigantic species, standing on average high. Placement in Phorusrhacidae and/or monophyly disputed. ** Genus ?'' Eleutherornis'' – Middle Eocene ( Bartonian) of Rhône, France and Baselland, Switzerland (a cariamiform, probably more related to '' Strigogyps'') * Subfamily Physornithinae — equivalent to Brontornithinae, if ''Brontornis'' is included within the family ** Genus '' Paraphysornis'' (Late Oligocene to Early Miocene (

Deseadan The Deseadan () age is a period of geologic time (29.0–21.0 Ma) within the Oligocene epoch of the Paleogene to the Early Miocene epoch of the Neogene, used more specifically within the SALMA classification of South America. It follows the Tingu ...

) Tremembé Formation of São Paulo State, Brazil) ** Genus '' Physornis'' (Middle to Late Oligocene (

) Sarmiento Formation of Santa Cruz Province, Argentina) * Subfamily Phorusrhacinae — giant species high (''Kelenken'' up to high), but somewhat slender and decidedly more nimble than the Brontornithinae ** Genus '' Devincenzia'' –

Early Pliocene Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

, possibly up to

** Genus '' Kelenken'' – Middle

( Colloncuran)

of Río Negro Province,

; largest known phorusrhacid ** Genus '' Phorusrhacos'' – Early to Middle Miocene ( Santacrucian) Santa Cruz Formation of Argentina ** Genus '' Titanis'' – Early Pliocene to Early Pleistocene (

Blancan The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of . * Subfamily Patagornithinae — intermediate sized and very nimble species, standing around high ** Genus '' Patagornis'' – Early to Middle Miocene ( Santacrucian–

) Santa Cruz Formation of Santa Cruz Province, Argentina – includes ''Morenomerceraria'', ''Palaeociconia'', ''Tolmodus'' ** Genus '' Andrewsornis'' – Middle to Late Oligocene (

) 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 high ** Genus '' Psilopterus'' – Middle Oligocene (

) Santa Cruz Formation and Late Miocene ( Chasicoan)

Arroyo Chasicó Formation Arroyo often refers to: * Arroyo (watercourse), an intermittently dry creek Arroyo may also refer to: Places United States * Arroyo, Pennsylvania * Arroyo, Puerto Rico, a municipality * Arroyo, West Virginia Spain * Arroyo (Santillana del Mar), ...

of southern and eastern Argentina respectively (Possible Late Pleistocene (

Lujanian The Lujanian age is a South American land mammal age within the Pleistocene and Holocene epochs of the Neogene, from 0.8–0.011 Mya (unit), Ma or 800–11 tya (unit), tya. It follows the Ensenadan. The age is usually divided into the middle Pleist ...

) records from Uruguay) ** Genus '' Procariama'' – Late Miocene to Early Pliocene ( Huayquerian–

Montehermosan The Montehermosan age is a period of geologic time (6.8–4.0 Mya (unit), Ma) within the Miocene and Pliocene epochs of the Neogene used more specifically with South American Land Mammal Ages. It follows the Huayquerian and precedes the Chapadmalal ...

) Cerro Azul and Andalhualá Formations of Catamarca Province, Argentina * Subfamily Mesembriornithinae — medium-sized species, standing high ** Genus '' Mesembriornis'' – Late Miocene to Late Pliocene (

) Monte Hermoso Formation of Argentina ** Genus '' Llallawavis'' – Late Pliocene (

Chapadmalalan The Chapadmalalan age is a period of geologic time (4.0–3.0 Ma) within the Pliocene epoch of the Neogene used more specifically with South American Land Mammal Ages. It follows the Montehermosan and precedes the Uquian age. Fossil content ...

) Playa Los Lobos Allo Formation of northeastern Argentina 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. Though traditionally considered as members of the Gruiformes, based on both morphological and genetic studies (the latter being based on the seriema) Cariamiformes may belong to a separate group of birds,

Australaves Australaves is a clade of birds, defined in 2012, consisting of the Eufalconimorphae (passerines, parrots and falcons) as well as the Cariamiformes (including seriemas and the extinct "terror birds"). They appear to be the sister group of Afroave ...

, and their closest living relatives, according to nuclear sequence studies, are a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

consisting of

Falconidae The falcons and caracaras are around 65 species of Diurnality, diurnal birds of prey that make up the family Falconidae (representing all extant species in the order (biology), order Falconiformes). The family likely originated in South America d ...

, Psittaciformes and

Passeriformes A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped') which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an anisodactyl arrangement of their ...

. The following cladogram follows the analysis of Degrange and colleagues, 2015:

Extinction

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

2.7 million years ago, carnivorous dogs, bears, and cats from North America were able to cross into South America, increasing competition. (They had been preceded by procyonids as early as 7.3 million years ago.) The population of phorusrhacids declined thereafter according to older hypotheses, suggesting that competition with newly arrived predators was a major contributor to their extinction. Similar ideas have been considered for sparassodonts and for South America's terrestrial sebecid crocodilians. However, the role of competitive displacement in South American predator lineages has been questioned by some researchers. 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), 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. 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, 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 coexisted for several million years with large canids and big cats like '' Xenosmilus'', before its extinction about 1.8 million years ago. Paleohistological analysis further refutes competitive replacement, as their uninterrupted growth patterns contrasts that of birds that inhabit islands or well adapted, stable ecosystems with a lack of strong predation pressure. So the authors concluded that their extinction was due to environmental conditions. 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 phorusrhacids went extinct over one million years before humans arrived. However, several fossil finds of smaller forms have been described from the late Pleistocene of

in South America. '' 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. Another unidentified smaller type which may be a possible psilopterine from the La Paz Local Fauna of

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, but the validity of this previous radiocarbon dating has been considered highly questionable due to the enamel's lack of collagen; 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.

Notes

References

External links

Hooper Museum

Terror Birds: Bigger and Faster
(

Science Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...

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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
xkcd Terror Bird
{{Taxonbar, from=Q752173 Extinct flightless birds Ypresian first appearances Pleistocene extinctions Apex predators Cenozoic birds of South America Taxa named by Florentino Ameghino Prehistoric bird families