The Snow Hill Island Formation is an Early Maastrichtian geologic

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

found on

James Ross Island James Ross Island () is a large island off the southeast side and near the northeastern extremity of the Antarctic Peninsula, from which it is separated by Prince Gustav Channel. Rising to , it is irregularly shaped and extends in a north–so ...

James Ross Island group The James Ross Island group () is a group of islands located close to the northeastern tip of the Antarctic Peninsula. The largest islands in the group are James Ross Island, Snow Hill Island, Vega Island, and Seymour Island. The islands lie to ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

. Remains of a

paravian Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the av ...

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 ...

Imperobator ''Imperobator'' ("powerful warrior") is a genus of probable unenlagiid Paraves, paravian theropod dinosaurs, that lived during the Maastrichtian age of the Late Cretaceous in what is now James Ross Island in Antarctica. ''Imperobator'' is one of ...

antarcticus''Ely & Case, 2019 have been recovered from it, as well as the

elasmaria Elasmaria is a clade of Ornithopoda, ornithopods known from Cretaceous deposits in the former Gondwana (South America, Antarctica, Australia, and possibly Africa) that contains many bipedal ornithopods that were previously considered Hypsilophodo ...

n ornithopods ''

Trinisaura ''Trinisaura'' is a genus of ornithopod dinosaur that lived during the late Campanian stage of the Late Cretaceous, Upper Cretaceous, around 73 to 72 million years ago in what is now James Ross Island off the coast of northern Antarctica near Pa ...

santamartaensis'', "Biscoveosaurus" and ''

Morrosaurus ''Morrosaurus'' is an extinct genus of herbivorous elasmarian dinosaur that lived in the late Cretaceous in Antarctica. The only known species is the type ''Morrosaurus antarcticus''. Discovery In 2002, the Argentine paleontologist Fernando ...

antarcticus'', the

ankylosauria Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs ...

n ''

Antarctopelta ''Antarctopelta'' (; meaning 'Antarctic shield') is a genus of ankylosaurian dinosaur, a group of large, quadrupedal herbivores, that lived during the Maastrichtian stage of the Late Cretaceous period on what is now James Ross Island, Antarctica ...

oliveroi'', and the shark ''

Notidanodon ''Notidanodon'' is an extinct genus of cow shark. Fossils ascribed to this genus are known from the Jurassic and Cretaceous periods. Recently, the genus underwent a major revision and was split into two after the erection of ''Xampylodon'' to ac ...

'' sp. Alongside these described genera are also the remains of indeterminate

elasmosaurids Elasmosauridae, often called elasmosaurs or elasmosaurids, is an extinct family (biology), family of plesiosaurs that lived from the Hauterivian Stage (stratigraphy), stage of the Early Cretaceous to the Maastrichtian stage of the Late Cretaceou ...

,O'Gorman, 2012, p.2

lithostrotia Lithostrotia is a clade of derived titanosaur sauropods that lived during the Early Cretaceous and Late Cretaceous. The group was defined by Upchurch ''et al.'' in 2004 as the most recent common ancestor of ''Malawisaurus'' and ''Saltasaurus'' an ...

n titanosaurs and an indeterminate

pterosaur Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...

. In the Herbert Sound Member of the Snow Hill Island Formation, bivalves,

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

s, and fish were found.O'Gorman, 2012, p.3

Fossil content

Invertebrates

Corals

Crustaceans

Mollusks

= Ammonites

= Bivalves

= Gastropods

= Nautilidaes

Vertebrates

Fish

Pterosaurs

Dinosaurs

= Ankylosaurs

= Ornithopods

= Sauropods

= Theropods

Plesiosaurs

Mosasaurs

Plants

During the Campanian–Maastrichtian, the Antarctic Peninsula supported temperate, humid forests dominated by podocarps, araucarian conifers, and a diversifying group of angiosperms. Key angiosperm families included

Nothofagaceae ''Nothofagus'', also known as the southern beeches, is a genus of 43 species of trees and shrubs native to the Southern Hemisphere, found across southern South America (Chile, Argentina) and east and southeast Australia, New Zealand, New Guin ...

Monimiaceae The Monimiaceae is a family (biology), family of flowering plants in the magnoliid Order (biology), order Laurales.Peter F. Stevens (2001 onwards). "Monimiaceae" At: Angiosperm Phylogeny Website. At: Botanical Databases At: Missouri Botanical Gar ...

Cunoniaceae Cunoniaceae is a family of 27 genera and about 335 species of woody plants in the order Oxalidales, mostly found in the tropical and wet temperate regions of the Southern Hemisphere. The greatest diversity of genera are in Australia and Tasmania ...

Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...

Myrtaceae Myrtaceae (), the myrtle family, is a family of dicotyledonous plants placed within the order Myrtales. Myrtle, pōhutukawa, bay rum tree, clove, guava, acca (feijoa), allspice, and eucalyptus are some notable members of this group. All ...

Lauraceae Lauraceae, or the laurels, is a plant Family (biology), family that includes the bay laurel, true laurel and its closest relatives. This family comprises about 2850 known species in about 45 genus (biology), genera worldwide. They are dicotyled ...

Atherospermataceae The Atherospermataceae, commonly known as the southern sassafrases, are a family (biology), family of broadleaf evergreen trees and shrubs. The family includes 14 species in seven genus, genera. The atherosperms are today mostly distributed in th ...

Winteraceae Winteraceae is a primitive family of tropical trees and shrubs including 93 species in five genera. It is of particular interest because it is such a primitive angiosperm family, distantly related to Magnoliaceae, though it has a much more south ...

, and extinct ''

Sassafras ''Sassafras'' is a genus of three extant and one extinct species of deciduous trees in the family Lauraceae, native to eastern North America and eastern Asia.Wolfe, Jack A. & Wehr, Wesley C. 1987. The sassafras is an ornamental tree. "Middle Eo ...

''-like forms. Another important group is

Asteraceae Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...

, with ''

Dasyphyllum ''Dasyphyllum'' is a genus of flowering plants in the family Asteraceae. It is distributed in South America, with several species in southeastern Brazil.Osmundaceae Osmundaceae (royal fern family) is a family of ferns containing four to six extant genera and 18–25 known species. It is the only living family of the order Osmundales in the class Polypodiopsida (ferns) or in some classifications the only ord ...

and

Gleicheniaceae The forked ferns are the family Gleicheniaceae, which includes six genera and about 160 known species. The formerly independent families Dicranopteridaceae and Stromatopteridaceae are generally included in the Gleicheniaceae, whereas the Dipteri ...

formed part of the understorey. Fossil evidence (wood, pollen, leaves) comes mainly from Seymour, Vega, James Ross, and Snow Hill islands. Forests were structurally similar to modern

Valdivian temperate forests The Valdivian temperate forests (NT0404) is an ecoregion on the west coast of southern South America, in Chile and Argentina. It is part of the Neotropical realm. The forests are named after the city of Valdivia. The Valdivian temperate rainfores ...

. The flora reflects a transition from gymnosperm-dominated to mixed angiosperm-conifer ecosystems under polar greenhouse conditions.

References

Bibliography

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