The La Meseta Formation is a sedimentary sequence deposited during the

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

. The formation is found on

Seymour Island Seymour Island or Marambio Island, is an island in the chain of 16 major islands around the tip of the Graham Land on the Antarctic Peninsula. Graham Land is the closest part of Antarctica to South America. It lies within the section of the isla ...

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

Description

La Meseta Formation lies unconformably on the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

Lopez de Bertodano Formation The Lopez de Bertodano Formation is a geological formation in the James Ross archipelago of the Antarctic Peninsula. The strata date from the end of the Late Cretaceous (upper-lower Maastrichtian stage) to the Danian stage of the lower Paleocene ...

. It is an approximately thick sequence of poorly consolidated

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

s and

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...

s. The

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

was probably coastal, deltaic or estuarine in character. The top of the sequence is an erosional unconformity to

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

glacial gravels. La Meseta Formation is one of the sequences that make up the fill of the

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...

James Ross Basin.

Fossil content

La Meseta Formation is extremely rich in fossils. Among mammals, the

meridiungulata South American native ungulates, commonly abbreviated as SANUs, are extinct ungulate-like mammals of controversial affinities that were indigenous to South America prior to the Great American Biotic Interchange. They comprise five major groups co ...

Antarctodon ''Antarctodon'' is an extinct genus of mammals from the Early Eocene (late Ypresian age). It is a basal astrapotherian which lived in what is now Seymour Island, Antarctic Peninsula, at that moment still connected to South America where most of ...

'' and ''

Trigonostylops ''Trigonostylops'' is an extinct genus of South American meridiungulatan ungulate, from the Late Paleocene to Late Eocene (Itaboraian to Tinguirirican in the SALMA classification) of South America (Argentina and Peru) and Antarctica ( Seymour Is ...

'' have been found in the formation.''Antarctodon''
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals ...

.org''Trigonostylops''
at

.org as well as marsupial

Microbiotheria Microbiotheria is an australidelphian marsupial order that encompasses two families, Microbiotheriidae and Woodburnodontidae, and is represented by only one extant species, the monito del monte, and a number of extinct species known from fossi ...

. It is famous for its penguin fossils, for example the two genera ''

Archaeospheniscus ''Archaeospheniscus'' is an extinct genus of large penguins. It currently contains three species, known from somewhat fragmentary remains. ''A. wimani'', the smallest species (about the size of a gentoo penguin), was found in Middle or Late Eocen ...

'' and ''

Palaeeudyptes ''Palaeeudyptes'' is an extinct genus of large penguins, currently containing four accepted species. They were probably larger than almost all living penguins, with the smaller species being about the size of an emperor penguin, and the largest s ...

''. Other bird fossils include ''

Dasornis ''Dasornis'' is a genus of the prehistoric pseudotooth birds. These were probably rather close relatives of either pelicans and storks, or of waterfowl, and are here placed in the order Odontopterygiformes to account for this uncertainty. ...

'', a genus of

pseudotooth bird The Pelagornithidae, commonly called pelagornithids, pseudodontorns, bony-toothed birds, false-toothed birds or pseudotooth birds, are a prehistoric family (biology), family of large seabirds. Their fossil remains have been found all over the wor ...

s. There are also an abundance of trace fossils.

Diplocraterion ''Diplocraterion'' is an ichnogenus describing vertical U-shaped burrows having a spreite (weblike construction) between the two limbs of the U. The spreite of an individual ''Diplocraterion'' trace can be either protrusive (between the paired ...

, Helminthopsis,

Muensteria ''Muensteria'' is the ichnogenus of a type of trace fossil that is found in sedimentary rocks, and is thought to represent the horizontal burrow of a marine invertebrate organism. It is a horizontal, non-branching, unlined, tube-like burrow char ...

, Oichnus,

Ophiomorpha ''Ophiomorpha'' is an ichnotaxon, usually interpreted as a burrow of an organism (specifically a crustacean) living in the near-shore environment. The burrow lining is more or less smooth on the inside, and densely to strongly mammalated or nod ...

Skolithos ''Skolithos'' (formerly spelled ''Scolithus'' or ''Skolithus'') is a common trace fossil ichnogenus that is, or was originally, an approximately vertical cylindrical burrow. It is produced by a variety of organisms in shallow marine environment ...

, Teredolites and Zapfella have been described. Over 35 species and 26 families of fish have been described from the

Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

Cucullaea bed.

Mammals

Astrapotheria

* ''

'' * '' Trigonostylopidae indet.''

Cetacea

* ''

Basilosaurus ''Basilosaurus'' (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). First described in 1834, it was the first archaeocete and prehistori ...

'' * ''

Llanocetus ''Llanocetus'' ( "Llano's whale" ) is a genus of extinct toothed baleen whales from the Late Eocene of Antarctica. The type species, ''Llanocetus denticrenatus'', reached gigantic proportions, with the juvenile specimen reaching an estimated i ...

Litopterna

* '' Notiolofos arquinotiensis'' * ''

Victorlemoinea ''Victorlemoinea'' is an extinct litoptern genus of the family Sparnotheriodontidae, that lived from the Early to Middle Eocene. Fossils of ''Victorlemoinea'' have been found in the Las Flores, Sarmiento and Koluel Kaike Formations of Argent ...

Marsupialia

* '' Marambiotherium glacialis'' * '' Woodburnodon casei''

Metatheria

* ''

Antarctodolops ''Antarctodolops'' is an extinct genus of polydolopimorphian metatherian similar to, but not closely related to, the living shrew opossums. It lived on Seymour Island, Antarctica in the Eocene.L. Chornogubsky, F. J. Goin, and M. Reguero. 2009. A ...

'' * '' Derorhynchus'' * '' Pauladelphys juanjoi''Antarctic Paleontological Heritage: Late Cretaceous–Paleogene vertebrates from Seymour (Marambio) Island, Antarctic Peninsula
. Advances in Polar Science. 30. 20 August 2019. doi:10.13679/j.advps.2019.0015. * '' Perrodelphys coquinense'' * '' Polydolops thomasi'' * '' Xenostylos peninsularis''

Birds

Sphenisciformes

* ''

Anthropornis ''Anthropornis'' is a genus of giant penguin that lived 45-33 million years ago, during the Late Eocene and the earliest part of the Oligocene.Myrcha, A., Jadwiszczak, P., Tambussi, C.P., Noriega, J.I., Gazdzicki, A., Tatur, A., and Valle, R.A. ...

'' # '' A. grandis'' # '' A. nordenskjoldi'' * ''

'' # '' A. lopdelli'' # '' A. wimani'' * '' Delphinornis larseni'' * ''

'' # '' P. antarcticus'' # '' P. gunnari'' # '' P. klekowskii''

Pelagornithidae

* ''

Amphibians

* ''

Calyptocephalella ''Calyptocephalella'' is a genus of frogs in the family Calyptocephalellidae. It is represented by a single living species, ''Calyptocephalella gayi'', commonly known as the helmeted water toad, Chilean helmeted bull frog or wide-mouth toad. Add ...

'' sp.

Fish

* ''

Otodus auriculatus ''Otodus auriculatus'' is an extinct species of large sharks in the genus ''Otodus'' of the family Otodontidae, closely related to the sharks of the genus ''Otodus'', and also closely related to the later species megalodon. Its teeth were large, ...

'' * ''

Hexanchus The sixgill sharks are a genus, ''Hexanchus'', of deepwater sharks in the family Hexanchidae. These sharks are characterized by a broad, pointed head, six pairs of gill slits, comb-like, yellow lower teeth, and a long tail. The largest species ca ...

'' sp. * ''

Pristiophorus ''Pristiophorus'' is a genus of sawsharks found in the Pacific, Atlantic and Indian oceans. Members of this genus differ from the Sixgill Sawshark ''(Pliotrema warreni The sixgill sawshark, ''Pliotrema warreni'' is a sawshark of the famil ...

laevis'' * cf. ''

Xiphiorhynchus ''Xiphiorhynchus'' is an extinct genus of prehistoric swordfish that lived from the Eocene until the Miocene. Unlike the modern swordfish, both the upper and lower jaws of ''Xiphiorhynchus'' were extended into blade-like points. Distribution ...

Plants

* '' Notonuphar antarctica'' * ?''

Nelumbo ''Nelumbo'' is a genus of aquatic plants with large, showy flowers. Members are commonly called lotus, though the name is also applied to various other plants and plant groups, including the unrelated genus '' Lotus''. Members outwardly resemb ...

'' sp.''''

Description

Fossil content

Mammals

Astrapotheria

Cetacea

Litopterna

Marsupialia

Metatheria

Birds

Sphenisciformes

Pelagornithidae

Amphibians

Fish

Plants

See also

References

Further reading