''Titanis'' (meaning "Titan" for the

Titans In Greek mythology, the Titans ( ; ) were the pre-Twelve Olympians, Olympian gods. According to the ''Theogony'' of Hesiod, they were the twelve children of the primordial parents Uranus (mythology), Uranus (Sky) and Gaia (Earth). The six male ...

Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...

) is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of phorusrhacid ("terror birds", a group originating in South America), 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 of large, predatory

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s, in the order

Cariamiformes Cariamiformes (or Cariamae) is an order of primarily flightless birds that has existed for over 50 million years. The group includes the family Cariamidae (seriemas) and the extinct families such as Phorusrhacidae, Bathornithidae, Idiornithid ...

that inhabited the United States from the early

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

. The first fossils were unearthed by amateur archaeologists Benjamin Waller and Robert Allen from the Santa Fe River in

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 ...

and were named ''Titanis walleri'' by ornithologist

Pierce Brodkorb William Pierce Brodkorb (September 29, 1908, Chicago – July 18, 1992, Gainesville, Florida) was an American ornithologist and paleontologist. Interested in birds since childhood, he was taught to prepare birds at the age of 16. Later, he rec ...

in 1963, the species name honoring Waller. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

material is fragmentary, consisting of only an incomplete right

tarsometatarsus The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bird bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) a ...

(lower leg bone) and

phalanx The phalanx (: phalanxes or phalanges) was a rectangular mass military formation, usually composed entirely of heavy infantry armed with spears, pikes, sarissas, or similar polearms tightly packed together. The term is particularly used t ...

(toe bone), but comes from one of the largest phorusrhacid individuals known. In the years following the description, many more isolated elements have been unearthed from sites from other areas of Florida,

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

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. The species was classified in the subfamily Phorusrhacinae, which includes some of the last and largest phorusrhacids like '' Devincenzia'' and '' Kelenken.'' Like all phorusrhacids, ''Titanis'' had elongated hind limbs, a thin pelvis, proportionally small wings, and a large skull with a hooked beak. It was one of the largest phorusrhacids, possibly similar in size to '' Phorusrhacos'' based on preserved material. More recent estimates placed ''Titanis'' at in height and over in body mass. Due to the fragmentary fossils, the anatomy is poorly known, but several distinct characters on the tarsometatarsus have been observed. The skull is estimated to have been between and in length, one of the largest known from any bird. Phorusrhacids are thought to have been ground predators or

scavengers Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding ...

, and have often been considered

apex predators 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 hi ...

that dominated

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 ...

South America in the absence of

placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...

mammalian predators, though they did co-exist with some large, carnivorous borhyaenid mammals. ''Titanis'' co-existed with many placental predators in North America and was likely one of several apex predators in its ecosystem. The tarsometatarsus was long and slender, like that of its relative ''Kelenken,'' which has been suggested to have been agile and capable of running at high speeds. Studies of the related '' Andalgalornis'' show that large phorusrhacids had very stiff and stress-resistant skulls; this indicates they may have swallowed small prey whole or targeted larger prey with repetitive strikes of the beak. ''Titanis'' is known from the Pliocene deposits of Florida, southern California, and southeastern Texas, regions that had large open savannas and a menagerie of mammalian megafauna. It likely preyed on mammals such as the extinct

armadillo Armadillos () are New World placental mammals in the order (biology), order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are dis ...

relatives '' Holmesina'' and '' Glyptotherium'', equids,

tapirs Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a Suidae, pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South America, South and Centr ...

capybaras The capybara or greater capybara (''Hydrochoerus hydrochaeris'') is the largest living rodent, native to South America. It is a member of the genus ''Hydrochoerus''. The only other extant member is the lesser capybara (''Hydrochoerus isthmiu ...

, and other Pliocene herbivores. ''Titanis'' is unique among phorusrhacids in that it is the only one known from North America, crossing over from South America before 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 ...

Discovery and age

The earliest discovery of ''Titanis'' fossils occurred in the winter of 1961/1962, when amateur archaeologists Benjamin Waller and Robert Allen were searching for artifacts and fossils using scuba gear in the Santa Fe River on the border of Gilchrist and Columbia Counties in Florida, United States. The two collectors donated their discoveries to the

Florida Museum of Natural History The Florida Museum of Natural History (FLMNH) is Florida's official state-sponsored and chartered natural history museum. Its main facilities are located at 3215 Hull Road on the campus of the University of Florida in Gainesville, Florida, Gaine ...

(UF) later along with bones of equids,

proboscidea Proboscidea (; , ) is a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. Three l ...

ns, and many other Floridan fossils from the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58latest Pleistocene. Waller and Allen's avian fossils consisted of only a distal

(lower leg bone) and a pedal phalanx (toe bone), deposited under specimen numbers UF 4108 and 4109 respectively. They remained without analysis in the museum's donations until they were recognized as unique by paleontologist Clayton Ray in 1962. He noticed the avian features and giant size of the fossils, which led him to believe they were from a phorusrhacid (or "terror bird", a group of large, predatory birds). Ray also noted their

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

origin; they were found in a sedimentary layer containing the equid ''

Nannippus ''Nannippus'' is an extinct genus of three-toed horse endemic to North America during the Miocene through Pleistocene, about 13.3—1.8 million years ago (Mya), living around 11.5 million years. This ancient species of three-toed horse grew up to ...

'' and "bone-crushing" dog '' Borophagus'', indicating that they originated from the upper part of the

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 . Ray presented the Santa Fe fossils to the museum's ornithologist

, who mistakenly believed that they were from

Rancholabrean The Rancholabrean North American Land Mammal Age on the geologic timescale is a North American faunal stage in the North American Land Mammal Ages chronology (NALMA),Sanders, A.E., R.E. Weems, and L.B. Albright III (2009) Formalization of the mid- ...

strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...

, an error which made it to the final publication. In that publication, Brodkorb erroneously classified it as a relative of rheas, though Ray pushed Brodkorb to assign the fossils to Phorusrhacidae. Brodkorb published his

description Description is any type of communication that aims to make vivid a place, object, person, group, or other physical entity. It is one of four rhetorical modes (also known as ''modes of discourse''), along with exposition, argumentation, and narr ...

in 1963, naming the new genus and species ''Titanis walleri''. The generic name, ''Titanis'', references the Greek Titans, due to the bird's large size, and the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, ''walleri'', honors Waller, one of the collectors of the

type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

. As suggested by Ray, Brodkorb grouped ''Titanis'' with the subfamily Phorusrhacinae within Phorusrhacidae, along with '' Phorusrhacos'' and '' Devincenzia''. This was the first discovery of phorusrhacids outside South America. ''Titanis'' has been found in five locales in Florida: Santa Fe River sites 1a and 1b and Inglis 1b, Citrus County; Port Charlotte, Charlotte County; and a shell pit in Sarasota County. Of the 40 Floridan specimens of ''Titanis'', 27 have been unearthed from the Santa Fe River, many of them collected in the 1960s and '70s following Brodkorb's description. The Santa Fe River specimens come from two localities within the river, 1a and 1b. The former locality is more productive, producing elements of ''Titanis'' including vertebrae, limb bones, and even parts of the skull. Inglis 1b was originally a

sinkhole A sinkhole is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline, enclosed depressions that are also known as shakeholes, and to openings where surface water ...

during the Pliocene, but became a sedimentary layer of clay that was uncovered during construction of the

Cross Florida Barge Canal The Marjorie Harris Carr Cross Florida Greenway is a protected green belt corridor, more than wide in places, that was the former route of the proposed Cross Florida Barge Canal. It is named for the leader of the opposition to the Cross Flo ...

by the

federal government A federation (also called a federal state) is an entity characterized by a political union, union of partially federated state, self-governing provinces, states, or other regions under a #Federal governments, federal government (federalism) ...

during the 1960s. A pair of graduate students from the

University of Florida The University of Florida (Florida or UF) is a public university, public land-grant university, land-grant research university in Gainesville, Florida, United States. It is a senior member of the State University System of Florida and a preem ...

were the first to discover fossils in the clay sediments in 1967, sparking a wave of large-scale excavations by curator David Webb of the Florida Museum of Natural History. Work on the site lasted from 1967 to 1973, during which over 18,000 fossils were collected. Of the many fossils, only 12 belonged to ''Titanis'', including

cervical vertebrae In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In saurop ...

, a

carpometacarpus The carpometacarpus is a bone found in the hands of birds. It results from the fusion of the carpal and metacarpal bone, and is essentially a single fused bone between the wrist and the knuckles. It is a smallish bone in most birds, generally fla ...

, and a

metatarsal The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...

. As for Port Charlotte, a single fossil, a partial pedal phalanx from the fourth digit, was donated to the UF in 1990. Another partial tarsometatarsus was reportedly found in a shell pit in Sarasota County, making it the only other tarsometatarsus known from ''Titanis''.

Texan and Californian discoveries

A newer discovery of ''Titanis'' was described in 1995; an isolated pedal phalanx that had been recovered from a sand and gravel pit near Odem along the

Nueces River The Nueces River ( ; , ) is a river in the U.S. state of Texas, about long. It drains a region in central and southern Texas southeastward into the Gulf of Mexico. It is the southernmost major river in Texas northeast of the Rio Grande. ''Nu ...

in San Patricio County, Texas. This was the first description of ''Titanis'' fossils from outside Florida. The pit was largely disorganized, with fossils dating to the Early Pliocene and Late Pleistocene jumbled together. The description followed Brodkorb's erroneous Late Pleistocene age assessment. Later analyses of

rare-earth element The rare-earth elements (REE), also called the rare-earth metals or rare earths, and sometimes the lanthanides or lanthanoids (although scandium and yttrium, which do not belong to this series, are usually included as rare earths), are a set o ...

s within the fossil demonstrated that the Texan ''Titanis'' derived from Pliocene rocks of the

Hemphillian The Hemphillian North American Stage on the geologic timescale is a North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 10,300,000 to 4,900,000 years BP. It is usually considered t ...

stage, a period preceding 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 ...

. This would make it the oldest estimate of a ''Titanis'' fossil at 5 million years old, compared to the Floridan fossils which are around 2.2–1.8 million years old, and therefore from the Blancan age. In 1961, while

fossil collecting Fossil collecting (sometimes, in a non-scientific sense, fossil hunting) is the Collecting, collection of the fossils for scientific study, hobby, or profit. Fossil collecting, as practiced by amateurs, is the predecessor of modern paleontolo ...

, G. Davidson Woodward acquired several avian fossils from sediments in the Pliocene-aged (3.7 million year old) strata of the Olla Formation in

Anza-Borrego Desert State Park Anza-Borrego Desert State Park (, ''Help:Pronunciation respelling key, AN-zə bə-RAY-goh'') is a California State Park located within the Colorado Desert of Southern California, United States. Created in 1932, the park takes its name from 18th ...

, California, including a wing bone found in association with the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

of a giant bird.Campbell Jr, K. E., Scott, E., & Springer, K. B. (1999)
A new genus for the incredible teratorn (Aves: Teratornithidae).
''Smithsonian Contributions to Paleobiology'', (89). The wing bone was referred to the teratorn '' Aiolornis'' at that time, an assessment backed by ornithologist Hildegarde Howard in 1972''.'' This was supported by later studies, but a 2013 paper by paleontologist Robert Chandler and colleagues assigned the premaxilla to ''Titanis'', the authors citing the bone's age and phorusrhacid features. The age of the Anza-Borrego premaxilla is estimated at 3.7 million years old, making it the oldest confirmed fossil of ''Titanis'', though the Texan specimen may be older.

Classification

During the early

, after the extinction of the non-avian 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 Dromornithidae, known as mihirungs (after Tjapwuring ''Mihirung paringmal'', "giant bird") and informally as thunder birds or demon ducks, were a clade of large, flightless Australian birds of the Oligocene through Pleistocene epochs. All are no ...

, 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, colloquially known as terror birds, are an extinct family of large carnivorous, mostly flightless birds that were among the largest apex predators in South America during the Cenozoic era. Their definitive fossil records range from ...

. Phorusrhacids are an extinct group within

, the only living members of which are the two species of seriemas in the family Cariamidae. Although phorusrhacids are the most taxon-rich group within Cariamiformes, their interrelationships are unclear due to the incompleteness of their remains. A lineage of related predatory birds, the

bathornithids Bathornithidae is an extinct family of birds from the Eocene to Miocene of North America. Part of Cariamiformes, they are related to the still extant seriemas and the extinct Phorusrhacidae. They were likely similar in habits, being terrestria ...

, occupied North America before the arrival of phorusrhacids, living from the Eocene to Miocene and filling a similar niche to cariamids. Cariama cristata-seriema-01

The oldest phorusrhacid fossils come from South America during the

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

(when the continent was an isolated island) and survived until the Pleistocene, eventually spreading to North America through ''Titanis''. Though fossils from Europe and Africa have been assigned to the group, their classification is disputed. It is unclear where the group originated; both cariamids and phorusrhacids may have arisen in South America, or arrived from elsewhere when southern continents were closer together or when sea levels were lower. Since phorusrhacids survived until the Pleistocene, they appear to have been more successful than the South American

metatherian Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well ...

thylacosmilid predators (which disappeared in the Pliocene), and it is possible that they competed ecologically with

predators that entered from North America in the Pleistocene. ''Titanis'' itself coexisted with a variety of placental mammalian predators, including

carnivora Carnivora ( ) is an order of placental mammals specialized primarily in eating flesh, whose members are formally referred to as carnivorans. The order Carnivora is the sixth largest order of mammals, comprising at least 279 species. Carnivor ...

ns like the saber-toothed cat ''

Smilodon ''Smilodon'' is an extinct genus of Felidae, felids. It is one of the best known saber-toothed predators and prehistoric mammals. Although commonly known as the saber-toothed tiger, it was not closely related to the tiger or other modern cats ...

'', cheetah-like '' Miracinonyx'', wolf-like '' Aenocyon'', and the short-faced bear ''

Arctodus ''Arctodus'' is an extinct genus of short-faced bear that inhabited North America during the Pleistocene (~2.6 Year#mya, Mya until 12,800 years ago). There are two recognized species: the lesser short-faced bear (''Arctodus pristinus'') and the gia ...

''. All of these genera, including the last phorusrhacids, went extinct during the

Late Pleistocene extinctions The Late Pleistocene to the beginning of the Holocene saw the extinction of the majority of the world's megafauna, typically defined as animal species having body masses over , which resulted in a collapse in faunal density and diversity acro ...

. Though for many decades the internal phylogenetics of Phorusrhacidae were uncertain and many

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

were named, they have received more analysis in the 21st century. ''Titanis'', however, has consistently been regarded as being within the subfamily Phorusrhacinae along with ''Phorusrhacos, Kelenken,'' and ''Devincenzia.''

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

ian paleontologist Herculano Alvarenga and colleagues published a

phylogenetic analysis In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical data ...

of Phorusrhacidae in 2011 that did not separate Brontornithinae, Phorusrhacinae, and Patagornithinae, resulting in ''Titanis'' in a

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...

(topology 1). In their 2015 description of '' Llallawavis,'' the Argentinian paleontologist Federico J. Degrange and colleagues performed a phylogenetic analysis of Phorusrhacidae, wherein they found Phorusrhacinae to be

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

, or an unnatural grouping (topology 2). Topology 1: Alvarenga ''et al.'' (2011) results Topology 2: Degrange ''et al.'' (2015) results

Description

Phorusrhacids were large,

flightless birds 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 ...

with long hind limbs, narrow pelvises, and proportionally small wings. They had elongated skulls ending in a thin, hooked beak. Overall, ''Titanis'' was very similar to the South American ''Phorusrhacos'' and ''Devincenzia'', its closest relatives. Little is known of its body structure, but it seems to have been less wide-footed than ''Devincenzia'', with a proportionally much stronger middle toe. In its initial description, ''Titanis'' has been suggested to be larger than the African

ostrich Ostriches are large flightless birds. Two living species are recognised, the common ostrich, native to large parts of sub-Saharan Africa, and the Somali ostrich, native to the Horn of Africa. They are the heaviest and largest living birds, w ...

and more than twice the size of South American rhea. Accurate scaling after the discovery of new material estimated its total height around tall. Though ''Titanis'' is suggested to be comparable in size to ''Phorusrachos'' based on comparing the dimensions of known specimens, researchers weren't able to definitively estimate the body mass of ''Titanis'' due to the fragmentary nature of the known specimens. In 1995, Jon A. Baskin proposed that a tall individual would have weighed , but the 2005 study which cited Baskin suggested it to be over . In spite of this, it would still make ''Titanis'' one of the largest phorusrhacids and birds known, only relatives like ''Devincenzia'' and ''Kelenken'' as well as some struthioniforms and gastornithiforms being larger.

Skull

Of the skull, only the premaxilla, frontal (top orbit bone), pterygoid (palate bone), quadrate (skull joint bone),

orbital process In the human skull, the zygomatic bone (from ), also called cheekbone or malar bone, is a paired irregular bone, situated at the upper and lateral part of the face and forming part of the lateral wall and floor of the orbit, of the temporal fossa ...

, and two quadratojugals (cheek bones) have been mentioned in scientific literature. The skull is estimated to have been between and in length, one of the largest known from any bird. These sizes are based on the size of quadratojugals from ''Titanis'' and the cranium of ''Phorusrhacos''. The premaxilla of ''Titanis'' is incomplete, consisting of its frontmost end including the characteristic long, sharp beak tip of Phorusrhacidae that would have been used for hunting. Its preserved length is with a height of with a triangular shape in vertical

cross-section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture and engineering 3D * Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) ...

. Sides of the fossil are flat bearing a large dorsal crest, as in other thin-skulled phorusrhacids like ''Phorusrhacos''. The culmen (upper arc) of the exposed premaxilla is identical to that in ''Patagornis marshi'', an Argentine phorusrhacid. The pterygoid is enlarged, as seen in other phorusrhacids, at in complete length with a medially placed joint for its articulation to the basipterygoid process. Two quadratojugals are preserved, both with different anatomies. The larger of the two has a more pronounced crest cranial to the articulation tubercular, whereas the smaller quadratojugal has a deep fossa instead of a crest. Potential

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

has been suggested due to the lack of signs of unfinished

ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the stu ...

development in the smaller quadratojugal, meaning they both come from adults. In the lower jaw, a partial mandible is known but it is unfigured and undescribed in scientific literature. Being a phorusrhacine, it would have had a long and narrow

symphysis A symphysis (, : symphyses) is a fibrocartilaginous fusion between two bones. It is a type of cartilaginous joint, specifically a secondary cartilaginous joint. # A symphysis is an amphiarthrosis, a slightly movable joint. # A growing together o ...

ending in a sharp tip pointing downward.

Postcranial skeleton

As for the postcranial anatomy, ''Titanis'' and other phorusrhacines were heavily built. They all preserve an elongated, thin tarsometatarsus that was at least 60% the length of the tibiotarsus. ''Titanis'' is distinguished from other phorusrhacines by the anatomy of its tarsometatarsus; the distal end of the mid-trochlea is spread out onto its sides and its slenderness compared to related genera of the same size. The pes is large and had three digits, the third of which had an enlarged

ungual An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropod Sauropoda (), whose members are known as sauropods (; ...

akin to that of

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 ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s. The spinal column is poorly known from ''Titanis'', though several

vertebra 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 spina ...

e have been collected. The cervical vertebrae are elongated anteroposteriorly and somewhat flexible, whereas the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

, sacral, and

caudal vertebrae Caudal vertebrae are the vertebrae of the tail in many vertebrates. In birds, the last few caudal vertebrae fuse into the pygostyle, and in apes, including humans, the caudal vertebrae are fused into the coccyx. In many reptiles, some of the caud ...

were more boxy and rigid. The dorsal vertebrae have tall neural spines atop the centra. The dorsal

ribs The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels ...

connected to the sacral ribs, creating a basketed underbelly. The wings are small and could not have been used for flight, but were much more strongly built than those of living

ratite Ratites () are a polyphyletic group consisting of all birds within the infraclass Palaeognathae that lack keels and cannot fly. They are mostly large, long-necked, and long-legged, the exception being the kiwi, which is also the only nocturnal ...

s. It also had a relatively rigid wrist, which would not have allowed the hand to fold back against the arm to the same degree as other birds. This led R. M. Chandler to suggest in a 1994 paper that the wings may have supported some type of clawed, mobile hand similar to the hands of non-avian

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaurs, such as the dromaeosaurs. It was later pointed out by Gould and Quitmyer in a 2005 study that demonstrated that this wing joint is not unique and is present in seriemas, which do not have specialized grasping hands. The wing bones articulated in an unusual joint-like structure, suggesting the digits could flex to some degree. Evidence of elongated quill-feathers are known from ''Patagornis'' and ''Llallawavis'', with large tubercles called quill knobs present on their ulnae. These quill knobs would have supported long

flight feather Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the tai ...

Paleobiology

Little is known about the paleobiology of ''Titanis'' due to a scarcity of fossil remains. Many of its habits are inferred based on related taxa like ''Kelenken'' and ''Andalgalornis.'' Features such as the pointed premaxillary beak tip and recurved pedal unguals are direct evidence of its carnivorous lifestyle.

Feeding and diet

Phorusrhacids are thought to have been terrestrial predators or

, and have often been considered

that dominated Cenozoic South America in the absence of placental mammalian predators. They co-existed with some large, carnivorous borhyaenid mammals for much of their existence. Earlier hypotheses of phorusrhacid feeding ecology were mainly inferred from their large skulls with hooked beaks rather than through detailed hypotheses and biomechanical studies. Detailed analyses of their running and predatory adaptations were only conducted from the beginning of the 21st century through the use of computer technology. Alvarenga and Elizabeth Höfling made some general remarks about phorusrhacid habits in a 2003 article. They were flightless, as evidenced by the proportional size of their wings and body mass, and the wing-size was more reduced in larger members of the group. These researchers pointed out that the narrowing of the pelvis, upper maxilla, and

thorax The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main di ...

could have been adaptations to enable the birds to search for and take smaller animals in tall plant growth or broken terrain. The large expansions above the eyes formed by the lacrimal bones (similar to what is seen in modern

hawks Hawks are bird of prey, birds of prey of the family Accipitridae. They are very widely distributed and are found on all continents, except Antarctica. The subfamily Accipitrinae includes goshawks, sparrowhawks, sharp-shinned hawks, and othe ...

) would have protected the eyes against the sun, and enabled keen eyesight, which indicates they hunted by sight in open, sunlit areas, and not shaded forests.

Leg function

In 2005, Rudemar Ernesto Blanco and Washington W. Jones examined the strength of the

tibiotarsus The tibiotarsus is the large bone between the femur and the tarsometatarsus in the leg of a bird. It is the fusion of the proximal part of the tarsus with the tibia. A similar structure also occurred in the Mesozoic Heterodontosauridae. These ...

(shin bone) of phorusrhacids to determine their speed, but conceded that such estimates can be unreliable even for extant animals. The tibiotarsal strength of ''Patagornis'' and an indeterminate large phorusrhacine suggested a speed of , and that of ''Mesembriornis'' suggested ; the latter is greater than that of a modern ostrich, approaching that of a cheetah, . They found these estimates unlikely due to the large body size of these birds, and instead suggested the strength could have been used to break the long-bones of medium-sized mammals, the size for example of a

saiga The saiga antelope (, ''Saiga tatarica''), or saiga, is a species of antelope which during antiquity inhabited a vast area of the Eurasian steppe, spanning the foothills of the Carpathian Mountains in the northwest and Caucasus in the southwes ...

Thomson's gazelle Thomson's gazelle (''Eudorcas thomsonii'') is one of the best known species of gazelles. It is named after explorer Joseph Thomson (explorer), Joseph Thomson and is sometimes referred to as a "tommie". It is considered by some to be a subspecies o ...

. This strength could be used for accessing the marrow inside the bones, or by using the legs as kicking weapons (like some modern ground birds do), consistent with the large, curved, and sideways compressed claws known in some phorusrhacids. They also suggested future studies could examine whether they could have used their beaks and claws against well-armored mammals such as

armadillos Armadillos () are New World placental mammals in the order Cingulata. They form part of the superorder Xenarthra, along with the anteaters and sloths. 21 extant species of armadillo have been described, some of which are distinguished by th ...

and glyptodonts. In a 2006 news article,

Luis Chiappe Luis María Chiappe (born 18 June 1962) is an Argentine paleontologist born in Buenos Aires who is best known for his discovery of the first sauropod nesting sites in the badlands of Patagonia in 1997 and for his work on the origin and early evol ...

, an Argentine paleontologist, stated that ''Kelenken'', a similar genus to ''Titanis'', would have been as quick as a

greyhound The English Greyhound, or simply the Greyhound, is a dog breed, breed of dog, a sighthound which has been bred for coursing, greyhound racing and hunting. Some are kept as show dogs or pets. Greyhounds are defined as a tall, muscular, smooth-c ...

, and that while there were other large predators in South America at the time, they were limited in numbers and not as fast and agile as the phorusrhacids, and the many

grazing In agriculture, grazing is a method of animal husbandry whereby domestic livestock are allowed outdoors to free range (roam around) and consume wild vegetations in order to feed conversion ratio, convert the otherwise indigestible (by human diges ...

mammals would have provided ample prey. Chiappe remarked that phorusrhacids crudely resembled earlier predatory dinosaurs like ''

Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...

'', in having gigantic heads, very small forelimbs, and very long legs, and thereby similar carnivore adaptations.

Skull and neck function

A 2010 study by Degrange and colleagues of the medium-sized phorusrhacid ''Andalgalornis'', based on

Finite Element Analysis Finite element method (FEM) is a popular method for numerically solving differential equations arising in engineering and mathematical models, mathematical modeling. Typical problem areas of interest include the traditional fields of structural ...

using

CT scans A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

, estimated its bite force and stress distribution in its skull. They found its bite force to be 133

Newtons The newton (symbol: N) is the unit of force in the International System of Units (SI). Expressed in terms of SI base units, it is 1 kg⋅m/s2, the force that accelerates a mass of one kilogram at one metre per second squared. The unit i ...

at the bill tip, and showed it had lost a large degree of intracranial immobility (mobility of skull bones in relation to each other), as was also the case for other large phorusrhacids such as ''Titanis''. These researchers interpreted this loss as an adaptation for enhanced rigidity of the skull; compared to the modern red-legged seriema and

white-tailed eagle The white-tailed eagle (''Haliaeetus albicilla''), sometimes known as the 'sea eagle', is a large bird of prey, widely distributed across temperate Eurasia. Like all eagles, it is a member of the family Accipitridae (or accipitrids) which also ...

, the skull of the phorusrhacid showed relatively high stress under sideways loadings, but low stress where force was applied up and down, and in simulations of "pullback" where the head returned to its normal position. Due to the relative weakness of the skull at the sides and midline, these researchers considered it unlikely that ''Andalgalornis'' engaged in potentially risky behavior that involved using its beak to subdue large, struggling prey. Instead, they suggested that it fed on smaller prey that could be killed and consumed more safely by swallowing it whole. Alternatively, if ''Andalgalornis'' did target large prey, Degrange ''et al.'' conjectured that it probably used a series of well-targeted repetitive strikes with the beak in an "attack-and-retreat" strategy. Struggling prey could also have been restrained with the feet, despite the lack of sharp talons. A 2012 follow-up study by Claudia Tambussi and colleagues analyzed the flexibility of the neck of ''Andalgalornis'' based on the morphology of its neck vertebrae, finding the neck to be divided into three sections. By manually manipulating the vertebrae, they concluded that the neck musculature and skeleton of ''Andalgalornis'' were adapted to carrying a large head and for raising the head after the neck had been fully extended. The researchers assumed same would be true for other large, big-headed phorusrhacids. A 2020 study of phorusrhacid skull morphology by Degrange found that there were two main morphotypes within the group, derived from a seriema-like ancestor. These were the "Psilopterine Skull Type", which was

plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, an ...

(more similar to the ancestral type), and the "Terror Bird Skull Type", which included ''Titanis'' and other large members, that was more specialized, with more rigid skulls. Despite the differences, studies have shown the two types handled prey similarly; the more rigid skulls and resulting larger bite force of the "Terror Bird" type would have been an adaptation to handling larger prey.

Paleoenvironment

During the Blancan stage, ''Titanis'' lived alongside both

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

mammals as well as new immigrants from Asia and South America. Because of this, the fauna of the Blancan starkly contrasted with the fauna of the Pleistocene and

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

. The localities in which ''Titanis'' is known are all tropical or subtropical in climate, with traditional interpretations indicating a habitat of dense forests and a variety of flora. In Inglis 1a specifically, previous studies have reported that

longleaf pine The longleaf pine (''Pinus palustris'') is a pine species native to the Southeastern United States, found along the coastal plain from East Texas to southern Virginia, extending into northern and central Florida. In this area it is also known as ...

flatwoods Flatwoods, pineywoods, pine savannas and longleaf pine–wiregrass ecosystem are terms that refer to an ecological community in the southeastern coastal plain of North America. Flatwoods are an ecosystem maintained by wildfire or prescribed fir ...

and pine-oak scrub are known to have occupied the area, similar to the modern flora. More recent interpretations suggest that the environment of Pliocene-Pleistocene Florida was a mosaic of different communities (i.e. a mixture of forests, savannas, wetlands, etc.), and that ''Titanis'' lived in areas of xeric thorn-scrubs and

savanna A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...

s. Similarly, the

Santa Cruz Formation The Santa Cruz Formation is a geological formation in the Magallanes Basin, Magallanes/Austral Basin in southern Patagonia in Argentina and adjacent areas of Chile. It dates to the late Early Miocene epoch, and is contemporaneous with the eponym ...

where '' Phorusrhacos'' was discovered also consisted of a variety of habitats, with ''Phorusrhacos'' suggested to live in open grasslands. During the Miocene-Pliocene climatic transition, the climate was cooler but temperatures did not reach those of the Pleistocene, creating a warm period. Sea levels were higher, but this was reversed at the end of the Pliocene during the beginning of large glaciations that fostered the Pleistocene's "Ice Age". The Blancan age strata of Florida from ''Titanis'' sites preserve over a hundred species and many different mammals. This includes extinct proboscideans and

perissodactyl Perissodactyla (, ), or odd-toed ungulates, is an order of Ungulate, ungulates. The order includes about 17 living species divided into three Family (biology), families: Equidae (wild horse, horses, Asinus, asses, and zebras), Rhinocerotidae ( ...

s represented by grazing equids and browsing

tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a Suidae, pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South America, South and Centr ...

s''.'' A wide array of

artiodactyls Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other thre ...

existed, including peccaries, camelids, pronghorns, and the extant

white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known Common name, commonly as the whitetail and the Virginia deer, is a medium-sized species of deer native to North America, North, Central America, Central and South America. It is the ...

''.''Morgan, G. S., & Hulbert Jr, R. C. (1995). "Overview of the geology and vertebrate biochronology of the Leisey Shell Pit local fauna, Hillsborough County, Florida". ''Bulletin of the Florida Museum of Natural History'', ''37''(1), 1–92. Armadillos and their relatives are also known such as a pampathere, a glyptodont, and dasypodids''.'' One of the largest groups known from the Blancan of Florida is the

ground sloth Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. They varied widely in size with the largest, belonging to genera '' Lestodon'', ''Eremotherium'' and ''Megatherium'', being around the size of elephants. ...

s represented by three families''.'' The carnivorans include borophagins,

hyaenids Hyenas or hyaenas ( ; from Ancient Greek , ) are feliformia, feliform carnivoran mammals belonging to the Family (biology), family Hyaenidae (). With just four extant species (each in its own genus), it is the fifth-smallest family in the orde ...

, and "saber-toothed" cats. Large

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s are represented by

capybara The capybara or greater capybara (''Hydrochoerus hydrochaeris'') is the largest living rodent, native to South America. It is a member of the genus '' Hydrochoerus''. The only other extant member is the lesser capybara (''Hydrochoerus isthmi ...

s and

porcupine Porcupines are large rodents with coats of sharp Spine (zoology), spines, or quills, that protect them against predation. The term covers two Family (biology), families of animals: the Old World porcupines of the family Hystricidae, and the New ...

s. Many fossils of smaller mammals like

shrew Shrews ( family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to dif ...

rabbits Rabbits are small mammals in the family Leporidae (which also includes the hares), which is in the order Lagomorpha (which also includes pikas). They are familiar throughout the world as a small herbivore, a prey animal, a domesticated form ...

, and

muskrat The muskrat or common muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic rodent native to North America and an introduced species in parts of Europe, Asia, and South America. The muskrat is found in wetlands over various climates ...

s have been found associated with ''Titanis.'' Along with mammals, a menagerie of reptiles including lizards, turtles, and snakes is known from fossils. There are abundant remains of avifauna, with thousands of known fossils, including

birds of prey Birds of prey or predatory birds, also known as (although not the same as) raptors, are hypercarnivorous bird species that actively predation, hunt and feed on other vertebrates (mainly mammals, reptiles and smaller birds). In addition to speed ...

, the teratorn ''

Teratornis ''Teratornis'' (Greek: "wonder" (teratos), "bird" (ornis)) is an extinct genus of huge North American birds of prey—the best-known of the teratorns—of which, two species are known to have existed: ''Teratornis merriami'' and ''Teratornis woo ...

'', one of the largest flight-capable birds known, and

turkeys The turkey is a large bird in the genus ''Meleagris'', native to North America. There are two extant turkey species: the wild turkey (''Meleagris gallopavo'') of eastern and central North America and the ocellated turkey (''Meleagris ocell ...

Great American Interchange

Great_American_Biotic_Interchange_examples

South America, the continent where phorusrhacids originated, was isolated after the breakup of the landmass

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

at the end of the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

era. This period of separation from the rest of the Earth's continents led to an age of unique mammalian and avian evolution, with the dominance of phorusrhacids and sparassodonts as predators in contrast to the North American placental carnivores. The fauna of North America was composed of living groups like canids, felids, ursids, tapirids, antilocaprids, and equids populating the region alongside now extinct families like the

gomphothere Gomphotheres are an extinct group of proboscideans related to modern elephants. First appearing in Africa during the Oligocene, they dispersed into Eurasia and North America during the Miocene and arrived in South America during the Pleistocene a ...

s, amphicyonids, and mammutids. Phorusrhacids evolved in South America to fill gaps in niches otherwise filled by placentals in other continents, such as that of apex predator. Flight-capable birds could more easily migrate between continents, creating a more homogenous avian fauna. The Great American Interchange took place between 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 ...

and Pliocene, though most species crossed at around 2.7 million years ago. The momentous final stage witnessed the movement of glyptodonts, capybaras, pampatheres, and marsupials to North America via the

, which connected South America to the rest of the Americas, and a reverse migration of ungulates, proboscideans, felids, canids, and many other mammal groups to South America. The oldest fossil of ''Titanis'' is estimated to be 5 million years old, at least half a million years older than the earliest date for the Isthmus's formation about 4.5–3.5 million years ago. How ''Titanis'' was able to traverse the gap to North America is unknown. A hypothesis made by a 2006 article suggested that it could have island-hopped through Central America and the Caribbean islands. ''Titanis'' is possibly not the only large animal to have done this; two genera of large ground sloth and a

procyonid Procyonidae ( ) is a New World family (biology), family of the order (biology), order Carnivora. It includes the Procyon (genus), raccoons, ringtails, cacomistles, coatis, kinkajous, olingos, and olinguitos. Procyonids inhabit a wide range of e ...

made it to North America millions of years before the volcanic formation of Panama. The period following the Isthmus's foundation saw the extinction of many groups, including the South American phorusrhacids; the last phorusrhacids went extinct in the Pleistocene. Human settlement in the Americas, climate change, and other factors likely led to the extinction of most of the remaining native South American mammal families.

Extinction

The extinction of ''Titanis'' and other phorusrhacids throughout the Americas was originally theorized to have been due to competition with large placental (

canid Canidae (; from Latin, ''canis'', "dog") is a family (biology), biological family of caniform carnivorans, constituting a clade. A member of this family is also called a canid (). The family includes three subfamily, subfamilies: the Caninae, a ...

felid Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...

, and possibly ursid) carnivores that occupied the same ancient terrestrial ecosystems during the Great American Interchange. However, this has been contested as ''Titanis'' had competed successfully against both groups for several million years upon entering North America. In South America, phorusrhacids were already on the decline prior to the Great American Interchange, further doubting competitive replacement. Brodkorb's description of ''Titanis'' as being from the latest Pleistocene, an error followed by later studies, postulated that it went extinct as recently as 15,000 BP (about 13,000 BCE). The rare-earth element analysis of ''Titanis'' fossils by MacFadden and colleagues in 2007 dispelled this, demonstrating that the genus lived during the Pliocene and earliest Pleistocene. Some phorusrhacid material from South America dates to the Late Pleistocene, younger than ''Titanis'', and close to the time of human arrival. Paleohistological analysis suggests environmental factors likely played a role in the extinction of phorusrhacids instead of competition with placental mammals.

References

{{Taxonbar, from=Q427685 Extinct flightless birds Bird genera Phorusrhacinae Pleistocene genus extinctions Pliocene birds of North America Pleistocene birds of North America Fossil taxa described in 1963 Taxa named by Pierce Brodkorb Fossils of California Fossils of Texas