Opalios

Opalios Temporal range: Late Cretaceous (Cenomanian), 100.2–96.6 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Monotremata
Superfamily:	Ornithorhynchoidea
Family:	†Opalionidae Flannery et al., 2024
Genus:	†Opalios Flannery et al., 2024
Species:	†O. splendens
Binomial name
†Opalios splendens Flannery et al., 2024

Opalios (meaning "opal") is an extinct genus of monotreme mammal from the Late Cretaceous (Cenomanian) Griman Creek Formation of Australia. The genus contains a single species, O. splendens, known from a fragmentary left dentary.

Discovery and naming

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Opalios type locality near Lightning Ridge, Australia

The Opalios holotype 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, Australia. The specimen consists of four broken pieces of the left dentary.^[1]

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 family Opalionidae within the Ornithorhynchoidea—the superfamily also containing modern echidnas and platypus—to house Opalios due to its similarity to both of these extant lineages. The generic name, Opalios, is a Greek word meaning "opal", referencing the holotype's opalized nature. The specific name, splendens, is a Latin word meaning "shining" or " distinguished", in reference to the holotype's striking translucency and size.^[1]

Opalios was nicknamed "echidnapus" (a portmanteau of "echidna" and "platypus") in the press following its description due to the specimen's similarities to both extant monotreme lineages.^[2] Several other monotremes are known from the Griman Creek Formation, including Dharragarra and Parvopalus—which were described in the same publication as Opalios—as well as Kollikodon, Steropodon, and Stirtodon.^[1]

References

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Mammalia

Kingdom: Animalia Phylum: Chordata Clade: Synapsida Clade: Therapsida Clade: Cynodontia Clade: Mammaliaformes
Synapsida see Synapsida Cynodontia see Cynodontia Mammalia see below↓

Mammalia
Australosphenida? †Ambondro †Tendagurutherium? Monotremata? †Henosferidae Asfaltomylos Henosferus †Ausktribosphenidae Ausktribosphenos Bishops? Kryoparvus? Monotremata †Kollikodontidae? Kollikodon Kryoryctes? Sundrius †Steropodontidae Parvopalus? Steropodon †Teinolophidae Stirtodon? Teinolophos Ornithorhynchoidea †Opalios Ornithorhynchidae †Dharragarra? †Monotrematum? †Obdurodon Ornithorhynchus †Patagorhynchus? Tachyglossidae †Megalibgwilia †Murrayglossus Tachyglossus Zaglossus †Allotheria? see Allotheria includes multituberculates Theriimorpha see below↓

Theriimorpha
Theriimorpha †Acinacodus †Amphidon †Amphilestes †Aploconodon †Chaoyangodens †Comodon †Condorodon †Dyskritodon? †Fruitafossor? †Hakusanodon †Indotriconodon †Juchilestes †Jueconodon †Kemchugia †Kryptotherium †Liaoconodon †Liaotherium †Manchurodon †Nakunodon †Phascolotherium †Sangarotherium †Tendagurodon †Allotheria? Monotremata? †Gobiconodontidae Fuxinoconodon Gobiconodon Hangjinia Huasteconodon? Meemannodon Repenomamus Spinolestes †Jeholodentidae Jeholodens Yanoconodon †Klameliidae? Ferganodon Klamelia †Triconodontidae Alticonodon Arundelconodon Astroconodon Corviconodon Eotriconodon Jugulator Meiconodon Priacodon Triconodon Trioracodon Victoriaconodon Volaticotheria? †Volaticotheria Argentoconodon Ichthyoconodon Triconolestes? Volaticotherium †Tinodontidae Gobiotheriodon? Tinodon Trishulotherium Yermakia Trechnotheria Monotremata? †Zhangheotheriidae Anebodon Kiyatherium Maotherium Ningchengodon Origolestes Zhangheotherium †Spalacotheriidae Akidolestes Aliaga Cifellitherium Heishanlestes Infernolestes Lactodens Shalbaatar Spalacolestes Spalacotheridium Spalacotherium Spalacotheroides Symmetrodontoides Symmetrolestes Yaverlestes Cladotheria see below↓

Cladotheria
†Dryolestida Brancatherulum? Dorsetodon Drescheratherium Euthlastus Henkelotherium Paurodon Tathiodon Dryolestidae Achyrodon Amblotherium Anthracolestes Beckumia Crusafontia Dryolestes Groebertherium? Guimarotodus Hercynodon Krebsotherium Lakotalestes? Laolestes Minutolestes Phascolestes Portopinheirodon Treslagosodon †Meridiolestida Amarillodon Austrotriconodon Bondesius Casamiquelia Cronopio Groebertherium? Lakotalestes? Leonardus Necrolestes Paraungulatum Quirogatherium Solanutherium Mesungulatoidea Coloniatherium Mesungulatum Orretherium Peligrotherium Reigitherium †Donodontidae Amazighodon Anoualestes Donodon Stylodens Prototribosphenida †Abelodon †Amphibetulimus †Amphitherium †Arguimus †Brancatherulum? †Chunnelodon †Magnimus †Minimus †Mozomus †Nanolestes †Palaeoxonodon †Vincelestes Monotremata? †Peramuridae Afriquiamus? Kouriogenys Peramuroides Peramus Tendagurutherium? Tribosphenida / Boreosphenida †Aegialodon †Argaliatherium †Brasilestes †Carinalestes †Eomaia †Holoclemensia †Hypomylos †Juramaia †Kermackia †Kielantherium †Pappotherium †Picopsis †Tirotherium †Tribactonodon Theria †Patagomaia Eutheria see Eutheria includes placentals Metatheria see Metatheria includes marsupials

Other taxa
Incertae sedis †Atlasodon †Chronoperates †Microderson †Thereuodon †Tingamarra Saint Bathans Mammal UA 8699 Other taxa Prototheria Yinotheria Eutriconodonta Amphilestidae Theriiformes Pantotheria Symmetrodonta Eupantotheria Paurodontidae Amphitheriidae Marsupionta