Phorusrhacidae (terror birds) 

1. Gastornis parisiensis 2. Phorusrhacos longissimus 3. Dromornis autralis 4. Kelenken guillermoi

Phorusrhacids, colloquially known as terror birds, are an extinct clade of large carnivorous flightless birds that were the largest species of apex predators in South America during the Cenozoic era; their temporal range covers from 62 to 1.8 million years (Ma) ago.
They were roughly 1–3 metres (3.3–9.8 ft) tall. Their closest modern-day relatives are believed to be the 80 cm-tall seriemas. Titanis walleri, one of the larger species, is also known in North America from Texas and Florida. This makes the phorusrhacids the only known large South American predator to migrate north during the Great American Interchange, which commenced after the Isthmus of Panama land bridge rose about 10 to 15 Ma.
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. Still, reports from Uruguay of new findings dating to 450,000 and 17,000 years ago, would imply that some phorusrhacids survived there until very recently (i.e., until the late Pleistocene); but this claim is debated. Phorusrhacids may have even made their way into Africa; the genus Lavocatavis was recently discovered in Algeria, but its status as a true phorusrhacid is questioned.A possible European form, Eleutherornis, has also been identified, suggesting that this group had a wider geographical range in the Paleogene. Based on Claudia P. Tambussi, Ricardo de Mendoza, Federico J. Degrange, and Mariana B. Picasso’s work, the phorusrhacid"s neck can be divided into three main regions. In the higher regions of the neck, the phorusrhacid has bifurcate neural spines (BNS), while it has high neural spines in its lower regions. This suggests that the phorusrhacid had a highly flexible and developed neck allowing it to carry its heavy head and strike with terrifying speed and power. Although the phorusrhacid externally looks like it has a short neck, its flexible skeletal neck structure proves that it can 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 can produce enough momentum and power to cause fatal damage to the Terror Bird’s prey.

Kelenken guillermoi, from the Langhian stage of the Miocene epoch, some 15 million years ago, discovered in Patagonia in 2006, represents the largest bird skull yet found. The fossil has been described as being a 71 cm (28 in), nearly intact skull. The beak is roughly 46 cm (18 in) long and curves in a hook shape that resembles an eagle"s beak. Most species described as phorusrhacid birds were smaller, 60–90 cm (2.0–3.0 ft) tall, but the new fossil belongs to a bird that probably stood about 3 m (9.8 ft) tall. Scientists theorize that the large terror birds were extremely nimble and quick runners able to reach speeds of 48 km/h (30 mph).
Most phorusrhacids were very fast and agile. All members possessed a large, sharp beak, a powerful neck and sharp talons. However, even with these attributes, the phorusrhacids are assumed to have preyed on smaller animals that could be dispatched with a minimum of struggle. 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. Generally speaking, it is thought that a terror bird would use its feet to injure prey by kicking it, and to hold the prey down and finish it off by pecking at it with its large beak. Larger prey may also have been attacked by pecking and kicking.
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. The anatomy of the typical phorusrhacid skull shows that it can handle this form of stress the best. This downward force would have allowed the phorusrhacid to shatter bones more easily, stunning its prey and making it easier to swallow whole. Some researchers think that the phorusrhacids closest relative, the seriema, acts very much like a phorusrhacid would have; picking up the prey and throwing them down then picking at them. If the prey was too large to swallow whole, the curved tip of the beak allowed the bird to pick at the prey and rip apart flesh, all using its very strong neck structure. They may have also used their claws to tear apart carcasses as well as helping them tear flesh.

1. Eleutherornis cotei 2. Psilopterus lemoinei 3. Procariama simplex 4. Mesembriornis milneedwardsii 5. Llallawavis scagliai 6. Patagorhacos terrificus 7. Andrewsornis abbotti 8. Patagornis marshii 9. Andalgalornis steulleti 10. Phorusrhacos longissimus 11. Devincenzia pozzi 12. Kelenken guillemori 13. Titanis walleri 14. Paraphysornis brasiliensis 15. Physornis fortis 16. Brontornis burmeisteri
From 27 million years to 2.5 million years ago, 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 savannah environment. However, as the Isthmus of Panama emerged, 2.5 million years ago, carnivorous dogs, bears, and cats from North America were able to cross into South America, increasing competition. As the population of phorusrhacids gradually decreased, this suggests that competition with other predators was a major influence on Phorusrhacidae extinction. Some researchers believe that the Phorusrhacidae"s extinction started at the beginning of the Pleistocene, 2.5 million years ago. South America was also home to other large carnivorous animals, including the sebecid crocodylomorphs, giant snakes and predatory relatives of marsupials, all of which were direct competitors with the phorusrhacids. This meant even more competition for the phorusrhacids. The combined competition of both new foreign and ancient endemic predators may have driven the phorusrhacids out of South America and eventually to extinction.

South American Phorusrhacids

Brontornis

The largest ever gruiform and largest phorusrhacid or "terror bird" (highly predatory, flightless birds of South America) was Brontornis, which was about 175 cm tall at the shoulder, could raise its head 2,8 metres above the ground an could have weighed as much as 400 kg.
It is known from bones, mainly of the legs and feet but also portions of some skulls and backbone, found in several localities of Santa Cruz Province.
B. burmeisteri was the second tallest species of phorusrhacid, with a height of around 2.8 m (9.2 ft) and the heaviest species of phorusrhacid with an estimated weight of 350–400 kg (770–880 lb) (Alvarenga & Hцfling, 2003), making it the third-heaviest bird ever according to current knowledge (after Aepyornis maximus and Dromornis stirtoni), and the most massive land predator of its time and place. Due to its bulk, it probably had a lifestyle between an ambush predator and one that actively chased prey, pouncing on the latter from a hideout and bringing it down by sheer force of attack after a short chase. In attacking prey (but probably not necessarily in a defensive situation, as it was too slow-moving) it most likely was the dominant carnivore of Miocene Patagonia, being able to kill even large animals such as the elephant-like Astrapotherium and in the predatory role being on par with a pack of Thylacosmilus (metatherian sabre-tooth). It coexisted with some slightly smaller and more active phorusrhacids like Phorusrhacos, but apparently became extinct before the appearance of the immense Argentavis, the largest flying bird ever.
Possibly, the fossils described as B. platyonyx represent another species; they are about one-third smaller than the largest Brontornis bones. It is much more likely, however, that they represent sexual dimorphism. In today"s hawks and owls, females are usually considerably larger than the males; this prevents overutilization of one size class of prey. It is not known whether phorusrhacid males or females would have been larger, but the fossils of the North American phorusrhacid Titanis also show considerable variation in size, suggesting that there was indeed at least a tendency for differently sized sexes.
Some recent workhas cast doubt on the hypothesis that Brontornis is a phorusrhacid; according to this research, it seems to actually be an anseriform. The other genera traditionally assigned to the subfamily Brontornithinae (Physornis and Paraphysornis) apparently are true phorusrhacids so the subfamily containing them had been proposed to be renamed Physornithinae, with Physornis fortis as the type. If valid, this would mean that there are three groups of giant basal anseriformes, in chronological order of divergence first the gastornids (relatives of Gastornis) then Brontornis and finally the mihirungs of Australia.
However, a subsequent analysis interprets Brontornis as having adaptations to great weight but exhibiting thoracic vertebrae diagnostic of phorusrhacids, reaffirming its placement within that group.

Phorusrhacos

Phorusrhacos longissimus (pronounced is an extinct, giant flightless predatory bird that lived in Miocene Patagonia. P. longissimus" closest living relatives are the much smaller seriemas. P. longissimus is thought to have lived in woodlands and grassland.
Phorusrhacos grew up to 2.5 metres (8.2 ft) tall and weighed approximately 130 kilograms (290 lb). They had enormous skulls up to sixty centimeters long, armed with powerful, hook-tipped beaks. The structure of the beak and the large claws on the toes show that they were carnivorous.
Like similar predatory birds of its day, Phorusrhacos was flightless with its wings greatly reduced in size. The wings of Phorusrhacos also had sharp hooks that seem to be more suited for gripping. These hooks have been suggested as being used to secure struggling prey as Phorusrhacos dispatched it with its beak, but it is also possible that they may have had a use in combat between Phorusrhacos individuals. Either purpose is possible, but birds like Phorusrhacos are usually depicted as hunting small to medium sized prey which may have been too small to be gripped with the wings.
The beak of Phorusrhacos is large and strongly curved to form a hook tip shape that is commonly seen in other birds that eat meat. This beak seems to have been the primary tool for killing prey with two main possible uses now generally accepted. The first method has been derived from observing the South American seriema birds which are thought to be the closest living relatives to terror birds like Phorusrhacos. Seriema birds pick up prey in their beaks and then throw it against the ground as hard as they can. Not only does this stun and kill prey, it breaks the bones so that small prey can be more easily swallowed as well as making it easier to use their claws to tear parts off prey too large to swallow. Many palaeontologists think that Phorusrhacos would have killed and eaten in a similar way, just on a larger scale.
The second method of killing prey involves using the beak to make precision strikes on critical body parts. As mentioned above, the beak is strongly curved and pointed, more so than necessary just for the purpose of feeding. It’s possible that this beak hook was brought down on top of prey for a quick strike to the back of the preys skull. This strike would have pierced the skull, causing damage to the brain resulting in instant death to the prey.
In order for Phorusrhacos to deliver a fatal strike it would first have to catch its prey, something it was well adapted to do. While the wings were too small for flight, the legs were very long and powerful. Across open ground Phorusrhacos would have easily been capable of chasing and catching up smaller mammalian prey. In hunting, Phorusrhacos may have stayed near thin outcroppings of shrubs and trees where its body form could more easily blend in with the tree trunks.Once prey approached close it could then ambush it with devastating speed before it had time to react. Once prey was caught and killed, Phorusrhacos probably used a combination of its sharp beak and the sharp claws of its feet to tear up the carcass so that it could be more efficiently eaten. While the beak of Phorusrhacos was sharp, the advantage of using the claws on its feet is clear because with these it could use its entire body weight (estimated to be as much as 130 kilograms) to push its claws through its preys body.
The suggestion has been made that Phorusrhacos and another ‘terror bird’ named Titanis are actually the same genus. However, while both birds are very similar, Titanis has a more robust build, particularly a shorter neck and heavier support for a skull.Because of this the majority of researchers continue to recognise Titanis as an independent genus, although because it is very similar it continues to belong to the same sub-family as Phorusrhacos, the Phorusrhacinae.

Andalgalornis

Andalgalornis has a more gracile build than many other South American ‘terror birds’ and this lightweight build is also reflected in the skull and beak. In depth analysis suggests that the beak was strongest when subjected to stresses from below rather than the sides. This meant that gripping and holding large prey was a risky business for Andalgalornis, but it does support two long held theories about how terror birds hunted and dispatched their prey. One is to focus upon smaller prey that could be easily killed by picking it up and throwing it hard against the ground and then swallowing the animal. The second is that the hook tip of the beak was used to strike down onto a preys’ skull to cause a mortal injury that would result in a quick death for the prey.


Devincenzia

Devincenzia was one of the larger terror birds but was still more gracile than some such as Brontornis. This implies that Devincenzia would have had a greater reliance upon speed and agility while hunting. Actually attacks upon prey may have been a series of heavy downward blows from its beak onto the head and neck of larger prey, while smaller prey may have been swallowed whole.
Devincenzia might even be larger than the increasingly famous Kelenken in terms of size, especially given that Keleneken has been estimated to be somewhere between 2.3 and 3 meters tall, depending upon the size of the body. However this turns out though, Devincenzia seems to ahve had a shorter skull given the the skull of Devincenzia is estimated to be around sixty-five centimetres long, while the skull of Kelenken is seventy-one centimetres long.
One first that the Devincenzia genus can claim is that it was the first terror bird to be discovered in Uruguay.

The immense phorushacid Kelenken with a skull 28 inches (71 cm) long (18 inches of which was beak), had the largest head of any known bird. Kelenken guillermoi is an giant flightless predatorybird of the extinct family Phorusrhacidae or "terror birds".

K. guillermoi lived in the Langhian stage of the Miocene, some 15 million years ago, in Argentina along with Argentavis. With a skull 28 inches (71 cm) long (including its 18 inch, 45.7 cm beak), it had the largest head of any known bird. It is the largest species of phorusrhacid. The tarsometatarsus was about 45 cm long.
It is not entirely clear how Kelenken captured and killed its prey. As a large flightless carnivore, Kelenken likely chased down and killed its prey with several bone-shattering blows from its massive beak. Another possibility is that it may have picked up its prey item, then proceeded to shake it vigorously in order break its back. It is also possible that Kelenken may have been a scavenger, driving off other predators from their kills with its impressive size.

Mesembriornis

Mesembriornis is a genus of intermediate-sized phorusrhacids that grew up to 1.5 metres in height. They represent a well-distinct lineage of terror birds, differing from the massive large groups and the smaller Psilopterinae. In general proportions, they most resembled the Patagornithinae which flourished somewhat earlier, mainly to the south of the range of Mesembriornis.
Two species are nowadays accepted, Mesembriornis incertus and Mesembriornis milneedwardsi. Mesembriornis lived on the pampa of E and NW Argentina from the Late Miocene to the Late Pliocene, roughly 10–2 million years ago. Together with the North American giant Titanis walleri, it was among the last terror birds alive.


Paraphysornis (Paraphysornis brasiliensis)

Paraphysornis is an extinct genus of giant flightless predatory birds of the family Phorusrhacidae or "terror birds" and the subfamily brontornithinae that lived in Brazil. Its length was about 2 meter,200 kg of weightand the skull had a length of 60 centimeter. The only known species is Paraphysornis brasiliensis. It lived 23 million years ago.
Paraphysornis was one of the more robust members of the phorusrhacid ‘terror birds’ and was most closely related to Physornis and Brontornis. Because of its large size and heavier build, Paraphysornis probably relied more upon ambush tactics to surprise prey rather than running it down over extended distances. Although this does not mean that Paraphysornis was afraid to give chase after prey.
 

Physornis

Physornis fortis is an extinct species of giant flightless predatory birds of the family Phorusrhacidae or "terror birds", within the subfamily Brontornithinae, that lived in Argentina. It lived from 28 to 23 million years ago, during the Oligocene
As a member of the Brontornithinae group of terror birds Physornis was one of the larger and more robust members of the larger group, the Phorusrhacidae, probably over 2 meters high.. As such it would have been related to Paraphysornis and Brontornis, and living during the Oligocene it was one of the earliest terror birds to roam and hunt in South America.

Patagornis