''Enantiornis'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

Enantiornithes 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 ...

. The type and only currently accepted species ''E. leali'' is from 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 th ...

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 ...

El Brete EL, El or el may refer to: Religion * El (deity), a Semitic word for "God" People * EL (rapper) (born 1983), stage name of Elorm Adablah, a Ghanaian rapper and sound engineer * El DeBarge, music artist * El Franco Lee (1949–2016), American po ...

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 ...

. It was described from specimen PVL-4035, a coracoid, proximal

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...

and proximal

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

found close to each other and suspected to represent the left shoulder of a single individual.

Description

The genus and the larger group it belongs to, get their name from the reversed scapula-coracoid connection they possess compared to modern birds and the hesperornithids that were their contemporaries: Enanti "opposite", ornis is "bird". Another left shoulder and wing, almost complete and found associated in one lump of rock, as well as a few isolated bones were also assigned to this species mainly based on size. It is among the largest enantiornithines discovered to date, with a length in life of around , hip height of , weight of , and wingspan comparable to

herring gull Herring gull is a common name for several birds in the genus ''Larus'', all formerly treated as a single species. Three species are still combined in some taxonomies: * American herring gull (''Larus smithsonianus'') - North America * European he ...

s, around . Its

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for ...

resembled that of a mid-sized

vulture A vulture is a bird of prey that scavenges on carrion. There are 23 extant species of vulture (including Condors). Old World vultures include 16 living species native to Europe, Africa, and Asia; New World vultures are restricted to North and ...

eagle Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, just ...

Taxonomy and phylogeny

''E. leali'' was possibly fairly closely related to ''

Avisaurus ''Avisaurus'' (meaning "bird lizard") is a genus of enantiornithine bird from the Late Cretaceous of North America. Discovery ''Avisaurus archibaldi'' was discovered in the Late Cretaceous Hell Creek Formation of North America (Maastrichtian, fr ...

'', another genus of probably carnivorous enantiornithines, though its exact relationship is unclear. It was placed in a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

of its own, Enantiornithidae. Other species from

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

that were previously placed in this genus are now split off. The former ''Enantiornis martini'' is now placed in ''

Incolornis ''Incolornis'' (meaning "inhabitant bird") is an extinct genus of basal birds from the Late Cretaceous (Coniacian, 89-86 mya). Remains have been found in the Bissekty Formation in Uzbekistan.Panteleyev, A.V. (1998) New species of enantiornithine ...

'', while the former ''Enantiornis walkeri'' is now tentatively assigned to ''

Explorornis ''Explorornis'' ("discovered bird", from Latin ''explōrō'' "to discover" and Ancient Greek ''ornis'' (''όρνις'') "bird") is a genus of Mesozoic birds which lived during the mid-late Turonian stage, around 90 million years ago, in the Biss ...

''. The reason for this is that these species were described when the diversity of enantiornithines was underestimated. As no hindlimb elements are known from ''Enantiornis'', it might include one of the El Brete enantiornithines known only from leg bones, namely ''

Lectavis ''Lectavis'' is a genus of enantiornithine birds. Their fossil bones have been recovered from the Late Cretaceous (Maastrichtian, c. 70.6 – 66 mya) Lecho Formation at ''estancia'' El Brete, Argentina. The genus contains a single species, '' ...

'', ''

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 ...

'' or ''

Yungavolucris ''Yungavolucris'' is a genus of enantiornithean birds. It contains the single species ''Yungavolucris brevipedalis'', which lived in the Late Cretaceous (Maastrichtian, c.70.6 – 66 mya). The fossil bones were found in the Lecho Formation at ' ...

''. However, these apparently were all smaller than ''Enantiornis''. Hindlimb material tentatively assigned to ''

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 ...

'' and ''

Elbretornis ''Elbretornis'' is an extinct genus of enantiornithine which existed in what is now Salta Province, Argentina during the late Cretaceous period. Etymology It was named by Cyril A. Walker and Gareth J. Dyke in 2009, and the type and so far ...

'' seems somewhat and a lot too small, respectively, to represent ''Enantiornis''. The cladogram below is from Wang ''et al.'', 2022: Key to letters: ''b'' = ''

Boluochia ''Boluochia zhengi'' was an enantiornithine bird. It lived during the Early Cretaceous in the time span 121.6-110.6 mya ( late Aptian- early Albian) and is known from fossils found in the Jiufotang Formation of Liaoning province, People's Republ ...

''
''c'' = ''

Cathayornis ''Cathayornis'' is a genus of enantiornithean birds from the Jiufotang Formation of Liaoning, People's Republic of China. It is known definitively from only one species, ''Cathayornis yandica'', one of the first Enantiornithes found in China. Se ...

''
''e'' = ''

Enantiophoenix ''Enantiophoenix'' is a genus of enantiornithine birds. Fossil remains were recovered from Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon () or the Lebanese Republic, is a country in Wes ...

''
''f'' = ''

Houornis ''Houornis'' is a genus of enantiornithean birds from the Jiufotang Formation of Liaoning, People's Republic of China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous c ...

''
''h'' = ''

Longipteryx ''Longipteryx'' is a genus of prehistoric bird which lived during the Early Cretaceous (Aptian stage, 120.3 million years ago). It contains a single species, ''Longipteryx chaoyangensis''. Its remains have been recovered from the Jiufotang Forma ...

''
''i'' = ''

Parabohaiornis ''Parabohaiornis'' is an extinct genus of bohaiornithid enantiornithean dinosaur known from the Early Cretaceous of Liaoning Province, northeastern China. It contains a single species, ''Parabohaiornis martini''. Discovery ''Parabohaiornis' ...

''
''j'' = '' Pterygornis''
''l'' = ''

Vorona ''Vorona'' ( ; Malagasy for "bird", ''V. berivotrensis'', "from Berivotra") is a monotypic genus of prehistoric birds. It was described from fossils found in a Maevarano Formation quarry near the village of Berivotra, Mahajanga Province, Madag ...

''
''m'' = ''

Yuanjiawaornis ''Yuanjiawaornis'' is an extinct genus of large enantiornithean bird known from the early Cretaceous of present-day China. It is monotypic, with only type species ''Y. virisosus'' known.Dongyu Hu, Ying Liu, Jinhua Li, Xing Xu & Lianhai Hou, 20 ...

''
''n'' = ''

References

Euenantiornitheans Maastrichtian life Cretaceous birds of South America Cretaceous Argentina Fossils of Argentina Lecho Formation Fossil taxa described in 1981 {{Theropod-stub