''Yungavolucris'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

enantiornithean The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and cla ...

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s. It contains the single

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

''Yungavolucris brevipedalis'', which lived in the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

(

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval ...

, c.70.6 – 66 mya). The fossil bones were found in the

Lecho Formation The Lecho Formation is a geological formation in the Salta Basin of the provinces Jujuy and Salta of northwestern Argentina. Its strata date back to the Early Maastrichtian, and is a unit of the Salta Group. The fine-grained bioturbated sandston ...

at ''

estancia An estancia is a large, private plot of land used for farming or raising cattle or sheep. Estancias in the southern South American grasslands, the ''pampas'', have historically been estates used to raise livestock, such as cattle or sheep. In Pu ...

'' El Brete,

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 ...

."''Yungavolucris brevipedalis''" means "Short-footed Yungas bird". The generic name, ''Yungavolucris'' is after the

Yungas The Yungas ( Aymara ''yunka'' warm or temperate Andes or earth, Quechua ''yunka'' warm area on the slopes of the Andes) is a bioregion of a narrow band of forest along the eastern slope of the Andes Mountains from Peru and Bolivia, and extends int ...

region + the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''volucris'', which translates to "bird" (literally "flyer"). The specific name ''brevipedalis'' is from the Latin ''brevis'', which means "short", + ''pedalis'', from the Latin ''pes'', meaning "foot".

Description

The only remains of ''Yungavolucris'' discovered so far consist of several tarsometatarsals, of which only the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

(PVL-4053) is nearly complete. These tarsometatarsals are unusually very stout and flat, and also very wide at the lower end. These specimens are small, just over 4 cm (1.5 inches) long, and if its legs and feet were not excessively shortened in relation to the body, the bird was about the size of a large blackbird in life. The width of the bone is considerable though, being about twice the width of the tarsometatarsals of '' Lectavis'' and ''

Soroavisaurus ''Soroavisaurus'' is a genus of enantiornithean birds related to '' Avisaurus''. It lived during the Late Cretaceous of Argentina. The only known species, ''S. australis'', is known from fossils collected from the Lecho Formation (Maastrichtian ...

'', two of its contemporaries. Thus, if the leg and foot only shortened and did not also become wider, it might be expected to have been a heavily built, sluggish and maybe even flightless bird the size of a large

chicken The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adu ...

: a length of , hip height of , and weight of .

Metatarsal The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...

IV ( the outermost bone of the tarsometatarsus) is very thin and diminished, but nevertheless about the same length as metatarsal III (the middle bone of the tarsometatarsus). In addition, the end of metatarsal III is bent outwards, to a position that would in other birds fall between toes 3 and 4. Metatarsal II (the innermost preserved bone of the tarsometatarsus) has a very broad and pulley-shaped trochlea (toe joint). A small bony bump (a dorsomedial projection) is present just above the inside edge of this trochlea. A ridge extends between the metatarsals II and III in the lower part of each bone. The middle of metatarsal II preserved a large tubercule (a node for muscle attachment) while the near part of metatarsal III possesses a thin ridge. No metatarsal I or

hallux Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being '' digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being '' pl ...

is preserved in any of the specimens. As in most enantiornitheans, no hypotarsus (a wide ridge on the back of the tarsometatarsus) is present.

Relationships

Irrespective of the peculiar

autapomorph In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

ies present in this taxon's remains, its affinities are uncertain. It has sometimes been compared to

avisaurids Avisauridae is a family of extinct enantiornithine dinosaurs from the Cretaceous period, distinguished by several features of their ankle bones. Depending on the definition used, Avisauridae is either a broad and widespread group of advanced e ...

, a group of late Cretaceous enantiornitheans which are also primarily known from tarsometatarsals. A small

phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

performed during its initial description in 1993 found several most parsimonious trees with conflicting results. Some placed it as a closer relative of avisaurids than '' Lectavis bretincola'' (an unusually long-legged enantiornithean discovered in the same deposit) was. However, other most parsimonious trees offered the opposite result, with ''Lectavis'' being a closer relative of avisaurids than ''Yungavolucris''. Since 1993, additional analyses have broadened the gap between ''Yungavolucris'' and avisaurids. Other enantiornitheans, such as '' Enantiophoenix'', '' Halimornis'', and ''

Concornis ''Concornis'' is a genus of enantiornithean birds which lived during the early Cretaceous period, in the late Barremian age about 125 million years ago. Its remains are known from the Calizas de La Huérgina Formation at Las Hoyas, Cuenca prov ...

'', have been found to be closer to '' Avisaurus'' than either ''Yungavolucris'' or ''Lectavis''. A close relationship between the two El Brete taxa and ''Avisaurus'' seems highly unlikely. As only the tarsometatarsus is known from ''Yungavolucris'', it might be the same species as one of the other El Brete enantiornitheans described based on forelimb bones. The size of ''Yungavolucris'' is hard to tell; the comparatively huge ''

Enantiornis ''Enantiornis'' is a genus of Enantiornithes. The type and only currently accepted species ''E. leali'' is from the Late Cretaceous Lecho Formation at El Brete, Argentina. It was described from specimen PVL-4035, a coracoid, proximal scapula ...

'' might be a match if ''Yungavolucris'' had short legs of normal width, but ''Enantiornis'' seems to be a fairly conventionally-built taxon. If ''Yungavolucris'' had both unusually short ''and'' wide legs, it might have been the size of the small species of ''

Martinavis ''Martinavis'' is a genus of enantiornithine birds which existed in what is now southern France, North America and Salta Province, Argentina during the late Cretaceous period. It was named by Cyril A. Walker, Eric Buffetaut and Gareth J. Dyke ...

'' or maybe the slightly larger '' Elbretornis''. However, these genera have

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 s ...

material tentatively referred to them, and while this material may not actually belong to ''Martinavis'' or ''Elbretornis'', it does not match the shape of a tibiotarsus that would form a working ankle with the ''Yungavolucris'' tarsometatarsus. A few studies have recovered it as a close relative of '' Grabauornis''.

References

{{Taxonbar, from=Q8061277 Euenantiornitheans Bird genera Maastrichtian life Cretaceous birds of South America Late Cretaceous animals of South America Cretaceous Argentina Fossils of Argentina Lecho Formation Yungas Fossil taxa described in 1993 Taxa named by Luis M. Chiappe

Description

Relationships

See also

References