This article is about an Antarctica sedimentary sequence. For the geological feature, see
Mesa. For other uses, see
Meseta.
The La Meseta Formation is a sedimentary sequence deposited during the Eocene on Seymour Island off the coast of the Antarctic Peninsula. It is noted for its fossils, which include both marine organisms and the only terrestrial vertebrate fossils from the Cenozoic of Antarctica.[2][4]
Description
La Meseta Formation lies unconformably on the Cretaceous Lopez de Bertodano Formation. It is an approximately 557 metres (1,827 ft) thick sequence of poorly consolidated sandstones and siltstones. The depositional environment was probably coastal, deltaic or estuarine in character. The top of the sequence is an erosional unconformity to Pleistocene glacial gravels.[3][2] La Meseta Formation is one of the sequences that make up the fill of the Late Jurassic to Paleogene James Ross Basin.[3]
Paleoenvironment
The terrestrial environment surrounding the deposition area is thought to have been a temperate polar forest, including podocarp and araucarian conifers, as well as Nothofagus.[5][6] Most of the fossilized woods and flowers discovered on Seymour Islands consist of extinct species of conifer trees and lilies during warm climate.[7][8]
Paleobiota
La Meseta Formation is extremely rich in fossils. Among mammals, the meridiungulata Antarctodon and Trigonostylops have been found in the formation.[9][10] as well as marsupial Derorhynchidae, Microbiotheria, and polydolopimorphia.[11][12] It is famous for its penguin fossils, for example the two genera Archaeospheniscus and Palaeeudyptes.[13][14] Other bird fossils include Dasornis, a genus of pseudotooth birds. There is also an abundance of trace fossils. Diplocraterion, Helminthopsis, Muensteria, Oichnus, Ophiomorpha, Skolithos, Teredolites and Zapfella have been described.[15] Over 35 species and 26 families of fish, which includes sharks, have been described from the Ypresian Cucullaea bed.[3][16]
Mammals
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Color key
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Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
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Meriduingulata
- Astrapotheria
- Litopterna
| Taxa |
Species |
Locality |
Stratigraphic position |
Material |
Notes |
Images
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| Notiolofos
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N. arquinotiensis
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Locality IAA 1/13 and DPV 16/84.
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Acantilados II, Campamento, Cucullaea I Allomember (Telm 4) and Submeseta Member (Telm 7).
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A Brachyodont lower right molar fragment, probably m1 or m2, preserves a portion of the talonid with most of the lingual side (MLP 13-I-25-1) and left M3 incomplete (MLP 95-I-10-6).
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A sparnotheriodontid litoptern.
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| N. regueroi
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Locality IAA 2/16
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Lower coquina bed of Cucullaea I Allomember.
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IAA-PV 173, Isolated complete left m3.
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| Victorlemoinea
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V. sp.
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Cucullaea I allomember (Telm 5).
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A sparnotheriodontid litoptern.
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Cetacean
| Taxa |
Species |
Locality |
Stratigraphic position |
Material |
Notes |
Images
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| Basilosaurus
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undetermined
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| Llanocetus
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L. denticrenatus
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Locality DPV 10/84 and DVP 13/24.
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Unit III Member and Telm 7.
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A partial mandible with two teeth (specimen USNM 183022) and an endocast of the braincase.
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a toothed baleen whale.
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| Zygorhiza
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undetermined
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Metatherians
- Derorhynchidae
| Taxa |
Species |
Locality |
Stratigraphic position |
Material |
Notes |
Images
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| Derorhynchus[17]
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D. minutus[17]
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Locality IAA 1/90.
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Allomember Cucullaea I (Telm 5).
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MLP 96-1-5-44, incomplete right horizontal ramus of the dentary fragment with m2-3.
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| Pauladelphys[17][18]
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P. juanjoi[17][18]
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Locality IAA 2/95 and IAA 1/90.
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Allomember Cucullaea I (Telm 5).
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An isolated lower molar (MLP 95-1-10-2) and an upper left molar (MLP 96-1-5-44).
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| Xenostylos
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X. peninsularis[17]
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Locality IAA 1/90.
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Allomember Cucullaea I (Telm 5).
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MLP 94-111-15-10, an isolated upper right molar.
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- Microbiotheria
| Taxa |
Species |
Locality |
Stratigraphic position |
Material |
Notes |
Images
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| Marambiotherium[17]
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M. glacialis[17]
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Locality IAA 1/90 and RV-8200.
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Cucullaea I allomember (Telm 5).
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MLP 95-1-10-1, a fragment of a right mandibular ramus with a complete m4 and the posterior alveolus of m3 and MLP 88-1-1-1, an edentulous left mandibular ramus with the alveoli for p3-m4.
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Members of Microbiotheria
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| Woodburnodon
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W. casei
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Locality IAA 1/95.
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Cucullaea I allomember (Telm 5).
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MLP 04-III-1-2, an isolated, worn upper right molar (M2 or M3).
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- Polydolopimorphia
Other mammals
| Taxa |
Species |
Locality |
Stratigraphic position |
Material |
Notes |
Images
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| Sudamerica
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S. ameghinoi
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Locality IAA 1/90 upper level.
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Cucullaea I Allomember.
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MLP 95-I-10-5, anterior part of a left dentary with the rodent-like incisor partially preserved.
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A gondwanathere
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| Meridiolestida?[20]
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Indeterminate
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Locality IAA 1/90 upper level.
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Cucullaea I Allomember.
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A single tooth, now lost.[20]
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| Xenarthra?
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Indeterminate.
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Locality S124.
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Cucullaea I Allomember/ Telm 4.
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TMM 44190-1, left metacarpal II and A phalanx and a partial tooth[20]
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Birds
Sphenisciformes
