''Olympidytes'' 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 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 ...

Plotopteridae Plotopteridae is an extinct family of flightless seabirds with uncertain placement, generally considered as member of order Suliformes. They exhibited remarkable convergent evolution with the penguins, particularly with the now extinct giant peng ...

, a family of large, flightless

marine bird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same envir ...

superficially similar to modern

penguin Penguins are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...

s but more closely related to

cormorant Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the International Ornithologists' Union (IOU) ado ...

s and

gannet Gannets are seabirds comprising the genus ''Morus'' in the family Sulidae, closely related to boobies. They are known as 'solan' or 'solan goose' in Scotland. A common misconception is that the Scottish name is 'guga' but this is the Gaelic n ...

s. It lived during the Late

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

or the Early

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

, in what is today the

State of Washington Washington, officially the State of Washington, is a state in the Pacific Northwest region of the United States. It is often referred to as Washington State to distinguish it from the national capital, both named after George Washington ...

and

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

History and etymology

The first specimen attributed to ''Olympidites'', a partial postcranial skeleton, was collected in 2012 by Bruce Thiel in Late Eocene to Early Oligocene sediments from the

Lincoln Creek Formation Lincoln Creek Formation (originally known as the Lincoln Formation) is a geologic formation in the state of Washington. It is part of the Belgian Basin and preserves fossils dating to between the Late Eocene-Early Miocene, recording an almost comp ...

. Another specimen attributed to the genus was collected by James L. Goedert in 2012, from Late

or Early

rocks from the Jansen Creek member of the Makah Formation, in the southwest of the

. In 2016, those remains were identified by Goedert and

Gerald Mayr Gerald Mayr is a German palaeontologist who is Curator of Ornithology at the Senckenberg Research Institute in Frankfurt am Main, Hesse. He has published extensively on fossil birds, especially the Paleogene avifauna of Europe.Mayr, Gerald (2016). ...

as belonging to a new genus and species of plotopterid, which they named ''Olympidytes thieli'', based on the holotype SMF Av 608, the fragmentary skeleton found by Thiel. In 2021, Mori Hirotsugu and Miyata Kazunori tentatively referred to the genus, as cf. ''Olympidytes'' sp., a fragmentary right tibiotarsus found in Early

deposits belonging to the lower member of the Kakinoura Formation near Saikai,

. With the redescription of the Japanese remains of ''

Tonsala ''Tonsala'' is an extinct genus of Plotopteridae, a family of flightless seabird similar in biology with penguins, but more closely related to modern cormorants. The genus is known from terrains dated from the Late Oligocene of the State of Washi ...

'' from Japan as the new genus '' Stenornis'', ''Olympidytes'' is the only genus of tonsalin plotopterid known from both sides of the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

. In 2021, a specimen once referred to ''Tonsala'' (now ''

Klallamornis ''Klallamornis'' is an extinct genus of Plotopteridae, a family of large, flightless birds related to modern cormorants, darters, gannets, and boobies. This genus included the largest North American plotopterids. Its remains can be found in Late ...

'') ''buchanani'' was redescribed as an indeterminate new species of plotopterid potentially belonging either to the genus ''Olympidytes'' or ''Klallamornis''.

Etymology

The genus name, ''Olympidytes'', is formed from the prefix "''Olymp-''", referring to the

Olympic Peninsula The Olympic Peninsula is a large peninsula in Western Washington that lies across Puget Sound from Seattle, and contains Olympic National Park. It is bounded on the west by the Pacific Ocean, the north by the Strait of Juan de Fuca, and the ...

in which the

paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...

was discovered, and the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

"''-dytes''", meaning "diver". The species name, ''thieli'', was given to honour Bruce Thiel, the collector and donator of the holotype.

Description

''Olympidytes'' was a comparatively small plotopterid, comparable in size with its relative ''

''. The

pygostyle Pygostyle is a skeletal condition in which the final few caudal vertebrae are fused into a single ossification, supporting the tail feathers and musculature. In modern birds, the rectrices attach to these. The pygostyle is the main component o ...

was more typical of that of leg-propelled diving birds like

s, rather than the elongated shape typical of modern wing-propelled divers, although this can be explained by the function held by the tail in terrestrial locomotion for the modern penguins, absent in plotopterids. The 111.2 cm long

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

was intermediate in its stoutness between ''

'' and its larger

ese relatives ''

Hokkaidornis ''Hokkaidornis'' is an extinct genus of Sphenisciformes, penguin-like plotopterid from the Late Oligocene of Hokkaido, Japan. History and etymology The first ''Hokkaidornis'' remains were discovered in sediments dated from the Late Oligocene of ...

'' and ''

Copepteryx ''Copepteryx'' is an extinct genus of flightless bird, flightless bird of the family Plotopteridae, endemic to Japan during the Oligocene living from 28.4 to 23 Annum, mya, meaning it existed for approximately . History and Etymology Remains of ...

''. The complete

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 ...

of the holotype, unique among all plotopterids, was similar but stouter than that of ''Tonsala''. The referred

tarsometatarsus 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) a ...

, although damaged, lacked a foramen vasculare distale, as in its relative ''

'', possibly suggesting that they were

sister taxa In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

. Cf ''Olympidytes'' sp., based on the specimen SM-SKT-1153 from

, likely represent a new species different from ''O. thieli''. While very similar in size and in shape to the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, the

lacked a deep groove located on the lateral side of the pons supratendineus where the tandon of the

fibularis brevis In human anatomy, the fibularis brevis (or peroneus brevis) is a muscle that lies underneath the fibularis longus within the lateral compartment of the leg. It acts to tilt the sole of the foot away from the midline of the body (eversion) and to ...

muscle would attach, a distinctive trait of the genus ''Olympidytes''.

Palaeoecology

Like its relative ''

'' and modern

s, ''Olympidytes'' is known to swallow pebbles, recovered as

gastrolith A gastrolith, also called a stomach stone or gizzard stone, is a rock held inside a gastrointestinal tract. Gastroliths in some species are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. In ...

s in association with the holotype. The presence of a well-developed trochlea cartiginalis tibialis, an adaptation usually present in hindlimb-propelled diving birds, and unusual for the wing-propelled plotopterid, may indicate that ''Olympidytes'' and its relative ''

'' were well adapted for both forms of propulsions. In the Late Eocene to Early Oligocene ocean preserved by the Jansen Creek member of the Makah Formation, ''Olympidytes'' coexisted with at least two other species of plotopterids, '' Klallamornis abyssa'' and ?''Klallamornis clarki''. With remains assigned tentatively to ''Olympidytes'' discovered in

, it is currently the only known genus of plotopterid known from both sides of the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

. The diversity of plotopterid on both sides of the

during the Late Eocene and Early Oligocene ; the group may have benefited from the global cooling event occurring during the Eocene-Oligocene boundary, which increase the presence of nutrients and the diversity of

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

in seas worldwide.

References

{{Taxonbar, from1=Q119495939 Fossil taxa described in 2016 Oligocene animals of North America Paleogene Japan Plotopteridae Extinct flightless birds Prehistoric bird genera