''Opalios'' (meaning "opal") is an

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 ...

genus of

monotreme Monotremes () are mammals of the order Monotremata. They are the only group of living mammals that lay eggs, rather than bearing live young. The extant monotreme species are the platypus and the four species of echidnas. Monotremes are typified ...

mammal from the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

(

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

) Griman Creek Formation of Australia. The genus contains a single species, ''O. splendens'', known from a fragmentary left

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

Discovery and naming

The ''Opalios''

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 ...

specimen, AM F132596–AM F132599, was discovered in 2001 in sediments of the Griman Creek Formation (Wallangulla Sandstone Member) near Lightning Ridge,

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

, Australia. The specimen consists of four broken pieces of the left

. In 2024, Flannery et al. described ''Opalios splendens'' as a new genus and species of early monotreme based on these fossil remains. They erected the new

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

family Opalionidae within the

Ornithorhynchoidea Ornithorhynchoidea is a superfamily of egg-laying mammals containing the only living monotremes, the platypus and the echidnas, as well as their closest fossil relatives, to the exclusion of more primitive fossil monotremes of uncertain affini ...

—the superfamily also containing modern

echidna Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the Family (biology), family Tachyglossidae , living in Australia and New Guinea. The four Extant taxon, extant species of echidnas ...

s and

platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypi ...

—to house ''Opalios'' due to its similarity to both of these extant lineages. The generic name, ''Opalios'', is a

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

word meaning "

opal Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...

", referencing the holotype's opalized nature. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

, '' splendens'', is a

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word meaning "shining" or " distinguished", in reference to the holotype's striking translucency and size. ''Opalios'' was nicknamed "echidnapus" (a

portmanteau In linguistics, a blend—also known as a blend word, lexical blend, or portmanteau—is a word formed by combining the meanings, and parts of the sounds, of two or more words together.

of "echidna" and "platypus") in the press following its description due to the specimen's similarities to both

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

monotreme lineages. Several other monotremes are known from the Griman Creek Formation, including ''

Dharragarra ''Dharragarra'' (meaning "platypus" in the Gamilaraay language) is an extinct genus of monotreme mammal from the Late Cretaceous (Cenomanian) Griman Creek Formation of Australia. The genus contains a single species, ''D. aurora'', known from a ...

'' and ''

Parvopalus ''Parvopalus'' (meaning "small opal") is an extinct genus of monotreme mammal from the Late Cretaceous (Cenomanian) Griman Creek Formation of Australia. The genus contains a single species, ''P. clytiei'', known from a partial left dentary. D ...

''—which were described in the same

publication To publish is to make content available to the general public.Berne Convention, articl ...

as ''Opalios''—as well as ''

Kollikodon ''Kollikodon'' is an extinct species of mammal, considered to be an early monotreme. It is known only from an opalised dentary fragment, with one premolar and two molars '' in situ'', as well as a referred maxillary fragment containing the las ...

'', ''

Steropodon ''Steropodon'' is a genus of prehistoric platypus-like monotreme, or Oviparity, egg-laying mammal. It contains a single species, ''Steropodon galmani'', that lived about 100.2–96.6 million years ago during the Cretaceous period, from early to m ...

'', and ''

Stirtodon ''Stirtodon'' is an extinct genus of monotreme mammal from the Late Cretaceous (Cenomanian) Griman Creek Formation of Australia. The genus contains a single species, ''S. elizabethae'', known from a large isolated premolar. ''Stirtodon'' may be ...

''.

References

{{Taxonbar, from1=Q126123780, from2=Q126123785 Prehistoric monotremes Prehistoric mammal genera Cenomanian life Cretaceous mammals of Australia Fossil taxa described in 2024 Taxa named by Tim Flannery Taxa named by Tom Rich Taxa named by Patricia Vickers-Rich