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

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

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

. 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 th ...

'' 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 Rio or Río is the Portuguese and Spanish word for "river". The word also exists in Italian, but is largely obsolete and used in a poetical or literary context to mean "stream". Rio, RIO or Río may also refer to: Places United States * Rio, Fl ...

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

. 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 dep ...

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

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

(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

and ''rhacos'', which was chosen for its use in the name of the type genus of the family, ''

Phorusrhacos ''Phorusrhacos'' ( ) is an extinct genus of giant flightless bird, flightless terror birds that inhabited South America during the Miocene epoch. ''Phorusrhacos'' was one of the dominant land predators in South America at the time it existed. It ...

''. The

species name In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...

"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 The quadratojugal is a skull bone present in many vertebrates, including some living reptiles and amphibians. Anatomy and function In animals with a quadratojugal bone, it is typically found connected to the jugal (cheek) bone from the front and ...

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 The diaphysis (: diaphyses) is the main or midsection (shaft) of a long bone. It is made up of cortical bone and usually contains bone marrow and adipose tissue (fat). It is a middle tubular part composed of compact bone which surrounds a centr ...

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 nume ...

'', ''

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'' measured up to tall at the hips and weighed aro ...

'' and ''

Mesembriornis ''Mesembriornis'' is a genus of intermediate-sized phorusrhacids that grew up to in height. They represent a well-distinct lineage of terror birds, differing from the massive large groups and the smaller Psilopterinae. In general proportions, t ...

''.

Paleoenvironment

''Patagorhacos'' was found in the Patagonian

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

litoptern Litopterna (from "smooth heel") is an extinct order of South American native ungulates that lived from the Paleocene to the Pleistocene-Holocene around 62.5 million to 12,000 years ago (or possibly as late as 3,500 years ago), and were also pres ...

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 ge ...

'', 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 n ...

('' Willidewu esteparius'' and ''

Australoprocta ''Australoprocta'' is an extinct genus of dasyproctid rodent that lived during the Early Miocene of what is now Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area ...

''),

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

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 ...

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

wading bird Birders in Canada and the United States refer to several families of long-legged wading birds in semi-aquatic ecosystems as waders. These include the families Phoenicopteridae (flamingos), Ciconiidae (storks), Threskiornithidae (ibises and s ...

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

{{Taxonbar, from1=Q27947437, from2=Q27972196 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