''Nanantius'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce 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 cl ...

avialan Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative defi ...

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

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

(

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

, c. 100–112 mya) of Australia.

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 precisely 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 a ...

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 the Pal ...

''. ''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 ...

and a cervical (neck)

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

hailing from the

Toolebuc Formation The Toolebuc Formation is a geological Formation (geology), 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,Weis ...

stratum. This

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

tibiotarsus ( QM F12992) was found at

Warra Station Warra is a rural town and locality in the Western Downs Region, Queensland, Australia. In the , the locality of Warra had a population of 180 people. Geography Warra is on the Darling Downs, a farming area in Queensland. It is on the Warrego ...

near

Boulia Boulia () is an outback town and locality in the Shire of Boulia, Queensland, Australia. In the , the locality of Boulia had a population of 314 people. Boulia is the administrative centre of the Boulia Shire, population approximately 600, whi ...

, in

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

. 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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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 avialan 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 ...

'' 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 The tarsometatarsus is a bone that is only found in the lower leg of birds and some non-avian dinosaurs. It is formed from the fusion of several bird bones found in other types of animals, and homologous to the mammalian tarsus (ankle bones) an ...

, 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 berivotrensis'' ( ; Malagasy for "bird", ''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 Provi ...

'', ''

Grabauornis ''Grabauornis'' is an extinct genus of enantiornitheans from the Early Cretaceous of China. The type species, ''Grabauornis lingyuanensis'', was named and described in 2014 by Johan Dalsätt, Per Ericson and Zhou Zhonghe. The genus name combin ...

'' and ''

Yungavolucris ''Yungavolucris'' is a genus of enantiornitheans. 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 '' es ...

''. ''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 (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

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

Eromanga Sea The Eromanga Sea was an inland sea across the Australian continent that formed in the Early Cretaceous. The sea extended from the Eromanga Basin northward to the Carpentarian Basin. Its southern extents comprised lagoons and rivers, and to the ea ...

, a shallow subtropical arm of the

Tethys Seaway The Tethys Ocean ( ; ), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean during much of the Mesozoic Era and early-mid Cenozoic Era. It was the predecessor to the modern Indian Ocean, the Mediterranean Sea, and the Eurasian ...

. 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 Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fo ...

with specimen number QM F16811.

References

{{Taxonbar, from=Q3071261 Enantiornithes Dinosaur genera Albian dinosaurs Taxa named by Ralph Molnar Fossil taxa described in 1986 Dinosaurs of Australia