''Nanantius'' 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 ...

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 ...

avialan Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used ...

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 lightweigh ...

" in the broad sense of the word) known from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

(

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

, c. 100–112 mya) of

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Specimens and species

The only valid species of ''Nanantius'' is ''Nantantius eos,' '' which was first described in 1986. A supposed second species, ''Nanantius valifanovi,'' has turned out to be a

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

of ''

Gobipteryx minuta ''Gobipteryx'' (from Gobi eferring to the Gobi Desert where it was first discovered and Greek pteryx “wing”) is a genus of prehistoric bird from the Campanian Age of the Late Cretaceous Period.Elżanowski, A. (1974): Preliminary note on th ...

''. ''N. eos'' was initially only known from an incomplete but elongated

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 ...

and a cervical (neck)

vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...

hailing from the

Toolebuc Formation The Toolebuc Formation is a geological formation that extends from Queensland across South Australia and the Northern Territory in Australia, whose strata date back to the Albian stage of the Early Cretaceous. Dinosaurs,Weishampel ''et al.'', 20 ...

stratum. This

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 several ...

tibiotarsus ( QM F12992) was found at Warra Station near

Boulia Boulia () is an outback town and locality in the Shire of Boulia, Queensland, Australia. In the , Boulia had a population of 301 people. Boulia is the administrative centre of the Boulia Shire, population approximately 600, which covers an area ...

, in

Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...

. In 1997, additional fossils from Canary Station in the same area of Australia were also placed into the genus ''Nanantius.'' One of these was a cervical (neck) vertebra, QM F12991, which was assigned to ''Nanantius eos''. The other bone was a partial left tibiotarsus (QM F31813) which was assigned to ''Nanantius'' but not placed within ''Nanantius eos'' due to possessing a few anatomical differences. In 2009, an unpublished dissertation written by Jingmai O'Connor reported that the holotype tibiotarsus and referred vertebra of ''N. eos'' have been lost. As it stands, ''Nanantius eos'' is one of the most fragmentary named species of enantiornithean.

Description

''Nanantius eos'' has been classified as an enanthiornithean, a

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 ...

group of primitive birds that did not survive the Cretaceous–Paleogene mass extinction. However, it is now known that the characters of the tibiotarsus are not sufficiently diagnostic to place a bird into the Enantiornithes. For example, the more modern genus ''

Apsaravis ''Apsaravis'' is a Mesozoic bird genus from the Late Cretaceous. The single known species, ''Apsaravis ukhaana'', lived about 78 million years ago, in the Campanian age of the Cretaceous period. Its fossilized remains were found in the Camel's ...

'' also possessed an "enantiornithean" tibiotarsus. Thus, although an enantiornithine affinity of ''Nanantius'' is likely - these birds were the dominant avian group in the Early Cretaceous, and the tibiotarsus is very similar to the doubtlessly enantiornithine ''Gobipteryx'' -, this placement is not certain until more diagnostic material, such as the characteristic tarsometatarsi, have been found. In Hartman et 2019 supplementary it is noted that the construction of the tibiotarsus is more typical of enantiornitheans than ornithurine birds ''Nanantius'' is tentatively recorded as part of a clade closely related to ''

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 ...

'', '' Grabauornis'' and ''

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 ' ...

''. ''N. eos'' was a small species, about the size of a blackbird; it probably looked like a miniature gull with clawed wings and a neck and head more similar to that of a feathered

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

. It presumably fed on marine invertebrates and small fish on the coast of what was then the

Eromanga Sea Eromanga or Erromanga may refer to: * Eromanga, Queensland, Australia **Eromanga Refinery, a small oil refinery in the town * Eromanga Basin, Australia ** Eromanga Sea, a prehistoric epicontinental sea that once covered the Eromanga Basin * Erroman ...

, a shallow subtropical arm of the Tethys Seaway. The theory that ''Nanantius'' were seabirds is evidenced by the fact that another tibiotarsus referable to this genus, and quite possibly to ''N. eos'' itself, was found in the gut of an

ichthyosaur Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...

with specimen number QM F16811.

References

{{Taxonbar, from=Q3071261 Euenantiornitheans Bird genera Cretaceous birds of Australia Paleontology in Queensland Fossil taxa described in 1986