Monday, September 28, 2015

Scaglia’s Terror Bird (Llallawavis scagliai)

Scaglia’s Terror Bird (Llallawavis scagliai) is the most recently discovered member of the terror bird family (Phorusrhacidae). This species known for a single near-complete, fully-articulated skeleton which even includes a preserved windpipe.
Drawing showing the skeletal anatomy of Llallawavis scagliai.
Figure 2 from Degrange et al., 2015.
The name Llallawa means “magnificent” in Quechua, in reference to the well-preserved nature of the remains. Avis is the Latin word for “bird”. The species name is after Galileo Juan Scalia, a naturalist and director of the Museo Municipal de Ciencias Naturales in Mar del Plata, Argentina. Fully translated, the binomial name therefore means “Scaglia’s Magnificent Bird”.

Habitat & Distribution
Scaglia’s Terror Bird lived during the late Pliocene in what is now Argentina. Its habitat was likely grassland and open woodland.

Physical Attributes
This species is known from a single, nearly complete articulated skeleton, the most complete of any terror bird known to date. Discovered in 2010 and described in 2015, the skeleton (shown above) was missing only some of the forelimb bones, toe bones, and the pygostyle*. This specimen is particularly valuable in that it includes the only complete trachea known for any terror bird, as well as intact sclerotic rings*.

Scaglia’s Terror Bird was one of the smaller members of its family, with an estimated body mass of 18kg (40lbs) and a hip height of about 90cm (3ft). When fully erect, it could have stood 120cm (4ft) tall at the top of its head. The body was lightly-built with long, slender legs for fast running. The skull was about 27cm (0.9ft) long with a beak that was relatively shallower and with a less prominent hook than that of other terror birds. Another notable feature of the bird’s head was its narial knob or bump just above its nostrils.

Ecology & Behavior
The structure of the inner ear suggests that Scaglia’s Terror Bird was adapted for very rapid and precise movements of the head and neck in response to visual and audio cues. Its low, narrow beak and lightweight body suggests that its diet consisted of relatively small prey items such as cavimorph rodents and other small mammals, as well as smaller birds and reptiles. It probably hunted in a manner similar to modern seriemas; after a short dash the prey would be pinned down before being picked up and violently slammed into the ground repeatedly. This action not only kills the victim, but also makes it easier to swallow due to the breaking of its bones.
Although it is currently impossible to reproduce the types of sounds Scaglia’s Terror Bird could produce, detailed analysis of its hearing capacity has shown that it could detect frequencies ranging from 380 to 4230 Hz, with a mean sensitivity of 2300 Hz. The bird’s own vocalizations, as well as those of its prey would have fallen within this range.

Hertz (Hz): a unit of frequency
Pygostyle: in birds, the fusion of several caudal (tail) vertebrae into a single bone.
Sclerotic ring: rings of interlocking bones which support the eyeball in several vertebrate groups.

References & Further Reading
Degrange FJ, Tambussi CP, Taglioretti ML, Dondas A, Scaglia F (2015). “A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds”. Journal of Vertebrate Paleontology 35(2): e912656 <Abstract>

Wednesday, September 2, 2015

Phorusrhacidae: the Terror Birds

The phorusrhacids, known commonly as the “terror birds”, were a diverse group of predatory flightless birds that inhabited South America from the early Paleocene to the late Pleistocene. The family Phorusrhacidae belongs to a larger order of birds known as the Cariamiformes or Cariamae, which originated during the late Cretaceous and appear to have become specialized for a primarily terrestrial lifestyle very early in their evolutionary history. In addition to South America, close relatives of terror birds were also distributed through Europe, Africa, and Antarctica during the Paleocene and Eocene. By the Oligocene, however, they had become extinct on all other continents except South America where they remained diverse.
Life restoration of Phorusrhacos longissimus
by Charles R. Knight, 1901. Wiki
The terror birds themselves were prominent components of the carnivore-omnivore guild in South America throughout the Cenozoic together with sebecid* crocodylians and sparassodont* marsupials. At least one species, Titanis walleri, managed to colonize the southern United States after the Isthmus of Panama connected the two Americas during the middle Pliocene. Species within this family range in mass from 5kg to about 400kg (10 to 880lbs). Terror birds continued to thrive in South America until they became extinct at the end of the Pleistocene together with many other types of large birds and mammals. The closest living relatives of the terror birds, and the only surviving representatives of the Cariamae, are the two species of seriema (Cariamidae) from South America. These modern birds are still capable of flight but prefer to hunt on the ground.
Red-legged Seriema (Cariama cristata), one
of two surviving representatives of the
Cariamae. Wiki
Anatomy & Action
Terror birds had proportionally large heads with deep, laterally flattened beaks with a hooked tip for tearing flesh. The inner structure of the beak was reinforced by bony struts and the skull bones were tightly fused together for strength. The pelvis was especially large to act as a counterbalance. They had long, powerful necks which would have been held in an S-shaped position when at rest. Detailed studies of the neck vertebrae shows that they were particularly well-adapted at making swift movements in the sagittal* plane, which is an ideal motion for striking prey. The caudal* vertebrae also appear to be somewhat more developed than those of modern flightless birds, implying that the tail, though highly reduced, may have been functional as a rudder of sorts during the pursuit of prey. As with all flightless birds, the bones of the forelimbs are greatly reduced in terror birds and were possibly involved in stability and maneuverability while running. The overall skeleton is much heavier and sturdier than what would be expected for a flying bird of the same size.

CT scan of the skull of the mid-sized terror
bird Andalgalornis steulleti. Wiki
Terror birds were primarily carnivorous, as evidenced by their large heads and massive, hooked beaks. Recent studies have shown that the sense of hearing in terror birds was well-developed and particularly sensitive to low-frequency sounds, suggesting that these birds utilized deep, resonant vocalizations to communicate with one another. CT scans of the brain cavities have shown that the areas of the brain that deal with visual information and problem-solving are also well-developed, while the sense of smell was relatively less so. It seems likely that terror birds hunted using vision and hearing as their primary senses. Once captured and dispatched, smaller prey items would have simply been swallowed whole, while larger meals were torn apart by the birds’ massive beak. Studies of terror bird limb muscular and proportions suggests that they were capable of exceptional feats of speed and agility.

Restored skeleton of Titanis walleri at the Florida Museum of
Natual History. Wiki
Terror Bird Groups
The family Phorusrhacidae is divided into five subfamilies; Psilopterinae, Brontornithinae, Patagornithinae, Mesembriornithinae, and Phorusrhacinae.
Restored skulls and heads of five terror bird species belonging to each of the subfamilies. 
A. Psilopterus lemoinei (Psilopterinae), B. Paraphysornis brasiliensis (Brontornithinae),
C. Andalgalornis steuletti (Patagornithinae), D. Llawllavis scagliai (Mesembriornithinae),
E. Kelenken guillermoi (Phorusrhacinae).
The longest-lived terror bird lineage, the Psilopterinae have a temporal range spanning from the late Paleocene to the early Pliocene. They are characterized by relatively slender, lightweight bodies, proportionally thin hindlimbs, and small overall size. Members of this subfamily range from 5 to 15kg in body mass. Known species include Paleopsilopterus itaboraiensis (early Paleocene), Psilopterus affinis (late Oligocene), P. bachmanni (late Miocene), P. lemoinei (late Miocene), and P. cozecus (late Miocene).

The brontornithines were large-bodied terror birds that existed during the Oligocene through to the early Miocene. Over time they appear to have been replaced by the Phorusrhacinae (see below) by the middle Miocene. Known species include Physornis fortis (late Oligocene), Paraphysornis brasiliensis (middle Oligocene to early Miocene), Brontornis burmeisteri (late Oligocene to middle Miocene).

Patagornithines were mid-sized terror birds with lean bodies and slender limb proportions. Known species include Andalgalornis steulleti (late Miocene to Pliocene), Andrewsornis abbotti (middle to late Oligocene), Patagornis marshi (middle Miocene).

The Mesembriornithinae are the shortest-lived and most diverse phorusrhacid subfamily, with a fossil record dating back to the late Miocene to the late Pliocene. Most are relatively small at around 10kg, while a few grew considerably large achieving estimated body weights of up to 70kg. It contains three genera and four species; Procariama simplex (late Miocene to late Pliocene), Llallawavis scagliai (Pliocene), Mesembriornis incertus (late Miocene to Pliocene), and M. milineedwardsi (late Miocene to Pliocene).

The Phorusrhacinae, together with the Brontornithinae, include some of the largest of the terror birds, with species ranging in mass from 100 to 400kg. This subfamily first appeared during the middle Miocene and persisted to the end of the Pleistocene. Known species include Phorusrhacos longissimus (middle Miocene), Kelenken guillermoi (middle Miocene), Devincenzia pozzi (late Miocene to early Pliocene), Titanis walleri (late Pliocene to early Pleistocene).

Caudal: of or referring to the tail of an animal.
Sagittal: a vertical plane that divides the body into right and left halves.
Sebecidae: an extinct group of terrestrial crocodilians endemic to South America until the late Miocene.
Sparassodonta: an extinct order of predatory mammals endemic to South America until the Pliocene.

References & Further Reading
Degrange FJ, Tambussi CP, Taglioretti ML, Dondas A, Scaglia F (2015). “A new Mesembriornithinae (Aves, Phorusrhacidae) provides new insights into the phylogeny and sensory capabilities of terror birds”. Journal of Vertebrate Paleontology 35(2): e912656 <Abstract>

Blanco RE & Jones WW (2013). “Terror birds on the run: a mechanical model to estimate its maximum running speed”. Proceedings of the Royal Society B 272: 1769-1773 <Full Article>

Angst D, Buffetaut E, Lecuyer C, Amiot R (2013). “Terror birds (Phorusrhacidae) from the Eocene of Europe imply trans-Tethys dispersal”. PLoS ONE 8(11): e80357 <Full Article>

Vezzosi RI (2012). “First record of Procariama simplex Rovereto, 1914 (Phorusrhacidae, Psilopterinae) in the Cerro Azul Formation (upper Miocene) of La Pampa Province; remarks on its anatomy, palaeogeography and chronological range”. Alcheringa: an Australasian Journal of Palaeontology 36(2): 157-169 <Full Article>

Tambussi CP, de Mendoza R, Degrange FJ, Picasso MB (2012). “Flexibility along the neck of the Neogene terror bird Andalgalornis steuletti (Aves Phorusrhacidae)”. PLoS ONE 7(5): e37701 <Full Article>

Degrange FJ & Tambussi CP (2011). “Re-examination of Psilopterus lemoinei (Aves, Phorusrhacidae), a late early Miocene little terror bird from Patagonia (Argentina)”. Journal of Vertebrate Paleontology 31(5): 1080-1092 <Abstract>

Mourer-Chauvire C, Tabuce R, Mahboubi M, Adaci M, Bensalah M (2011). “A Phororhacoid bird from the Eocene of Africa”. Naturwissenschaften 98: 815-823 <Full Article>

Degrange FJ, Tambussi CP, Moreno K, Witmer LM, Wroe S (2010). “Mechanical analysis of feeding behavior in the extinct “terror bird” Andalgalornis steulleti (Gruiformes: Phorusrhacidae)”. PLoS ONE 5(8): e11856 <Full Article>

Alvarenga H, Jones W, Rinderknecht A (2010). “The youngest record of phorusrhacid birds (Aves, Phorusrhacidae) from the late Pleistocene of Uruguay”. Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 256(2): 229-234 <Full Article>

Bertelli S, Chiappe LM, Tambussi C (2007). “A new phorusrhacid (Aves: Cariamae) from the middle Miocene of Patagonia, Argentina”. Journal of Vertebrate Paleontology 27(2): 409-419 <Full Article>

Chiappe LM & Bertelli S (2006). "Skull morphology of giant terror birds". Nature 443: 929 <Full Article>

Alvarenga HMF, Höfling E (2003). "Systematic revision of the Phorusrhacidae (Aves: Ralliformes)". Papéis Avulsos de Zoologia 43(4): 55–91 <Full Article>

Baskin JA (1995). "The giant flightless bird Titanis walleri (Aves: Phorusrhacidae) from the Pleistocene coastal plain of south Texas". Journal of Vertebrate Paleontology 15(4): 842-844 <>

Brodkorb P (1963). "A giant flightless bird from the Pleistocene of Florida". The Auk 80(2): 111-115 <Full Article>

Patterson B (1941). "A new phororhacoid bird from the Deseado formation of Patagonia". Geological Series of Field Museum of Natural History 8(8): 49-54 <Full Article>