''Patagorhacos'' is an extinct genus of medium-sized phorusrhacid from the early

Miocene The Miocene ( ) is the first 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 means "less recen ...

of Patagonia. Currently only the single species ''Patagorhacos terrificus'' is known, which is represented by two highly fragmentary specimen, one belonging to the back of the skull and the other being the distal end of a leg bone. It was described together with the contemporary

rheid In geology, a rheid is a substance whose temperature is below its melting point and whose deformation by viscous flow during the time of observation is at least three orders of magnitude (1,000×) greater than the elastic deformation under the ...

'' Opisthodactylus horacioperezi''.

History and naming

Fossil remains of this phorusrhacid have been discovered in Paso Córdoba, a Natural Protection area in the Rio Negro Province of

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. The rocks of the area belong to the

Chichinales Formation The Chichinales Formation is a geological formation in Río Negro Province, Argentina which dates from the Late Oligocene to the Early Miocene, around 23 to 17.5 million years ago. It predominantly consists of pyroclastic deposits, which were depo ...

, which dates to the early Miocene (Colhuehuapian in accordance with South American land mammal age (SALMA) classification. ''Patagorhacos'' is known from only two specimens. The holotype (MPCN-PV-377) is the distal end of a right

quadrate Quadrate may refer to: * Quadrate bone * Quadrate (heraldry) * Quadrate lobe of liver * Quadrate tubercle The quadrate tubercle is a small tubercle found upon the upper part of the femur. It serves as a point of insertion of the quadratus femori ...

, while the single referred specimen consists of the distal end of an

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

(MPCN-PV-379). Despite the lack in overlap, the ulna was assigned to ''Patagorhacos'' for its presence in the same locality and strata as the holotype quadrate and the fact that its size is consistent with the type specimen. The name ''Patagorhacos'' is a combination of Patagonia and ''rhacos'', which was chosen for its use in the name of the type genus of the family, '' Phorusrhacos''. The species name "terrificus" was chosen to represent the "terrific" nature of phorusrhacids.

Description

The quadrate of ''Patagorhacos'' is a robust bone belonging to a medium-sized Phorusrhacid. The body is comparably thin and compressed with strongly concave inner and outer margins. The pterygoid condyle meanwhile is strongly convex and very prominent, with a well-developed egg-shaped fossa on its rostrodorsal edge. In proximity to the condyle and separated by a thin bone wall are two more depressions, likely pneumatic fossae. The cotyle that receives the quadratojugal is deep and ovoid in shape and located above the lateral condyle. Towards the distal end of the bone three condyles can be seen, one medial, one lateral and one caudal, each separated through each other by grooves of varying width and depth. The ulna referred to Patagorhacos is poorly preserved and suffered heavily from erosion. However, it can be determined that the diaphysis was rather thin and the dorsal condyle well developed. When viewed from the side it's notably less prominent than that of ''

Patagornis ''Patagornis'' is a genus of extinct flightless predatory birds of the family Phorusrhacidae. Known as "terror birds", these lived in what is now Argentina during the Early and Middle Miocene; the Santa Cruz Formation in Patagonia contains numer ...

'', ''

Paraphysornis ''Paraphysornis'' is an extinct genus of giant flightless terror birds that inhabited Brazil during Late Oligocene or Early Miocene epochs. Although not the tallest phorusrhacid, ''Paraphysornis'' was a notably robust bird, having short and robus ...

'' and '' Mesembriornis''.

Paleoenvironment

''Patagorhacos'' was found in the Patagonian

, which is mostly known for its fossil mammals. The local fauna includes astrapotheres, the

litoptern Litopterna (from grc, λῑτή πτέρνα "smooth heel") is an extinct order of fossil hoofed mammals from the Cenozoic era. The order is one of the five great orders of South American ungulates that were endemic to the continent, until th ...

Cramauchenia ''Cramauchenia'' is an extinct genus of litoptern South American ungulate. ''Cramauchenia'' was named by Florentino Ameghino. The name has no literal translation. Instead, it is an anagram of the name of a related genus ''Macrauchenia''. This g ...

'', the notoungulates ''

Colpodon ''Colpodon'' is an extinct genus of herbivorous mammal, belonging to the order Notoungulata. It lived during the Early Miocene, in what is today Argentina and Chile, in South America. Description This animal is almost exclusively known from cra ...

'' (a leontiniid) and '' Cochilius volvens'' (an interatheriid),

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

('' Willidewu esteparius'' and '' Australoprocta''),

xenarthrans Xenarthra (; from Ancient Greek wikt:ξένος, ξένος, xénos, "foreign, alien" + wikt:ἄρθρον, ἄρθρον, árthron, "joint") is a major clade of Placentalia, placental mammals native to the Americas. There are 31 living species: ...

and borhyaenoids. Bird remains from the formation are comparatively poor. A part of a

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 sm ...

has previously been classified as an undetermined species of psilopterine phorusrhacid, a relative of ''Patagorhacos''. Other birds include an undetermined

wading bird 245px, A flock of Dunlins and Red knots">Red_knot.html" ;"title="Dunlins and Red knot">Dunlins and Red knots Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflat ...

and '' Opisthodactylus horacioperezi'', a species of rhea. During the Miocene the area likely consisted of open but wooded environment with temperate climate and a proximity to freshwater.

References

{{Cariamiformes, C., state=collapsed Phorusrhacidae Prehistoric bird genera Extinct flightless birds Miocene birds of South America Colhuehuapian Neogene Argentina Fossils of Argentina Fossil taxa described in 2015 Chichinales Formation