La Meseta Formation
The La Meseta Formation is a sedimentary sequence deposited during much of the Paleogene 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.
In some treatments, the La Meseta Formation is restricted to just the older Thanetian to Lutetian-aged strata, with the younger Bartonian to Rupelian strata treated as the overlying Submeseta Formation. However, other papers instead treat the Submeseta Formation as an allomember of the La Meseta Formation.
Description
La Meseta Formation lies unconformably on the Cretaceous Lopez de Bertodano Formation. It is an approximately 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. La Meseta Formation is one of the sequences that make up the fill of the Late Jurassic to Paleogene James Ross Basin.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. Most of the fossilized woods and flowers discovered on Seymour Islands consist of extinct species of conifer trees and lilies during warm climate.Paleobiota
La Meseta Formation is extremely rich in fossils. Among mammals, the meridiungulata Antarctodon and Trigonostylops have been found in the formation. as well as marsupial Derorhynchidae, Microbiotheria, and polydolopimorphia. It is famous for its penguin fossils, for example the two genera Archaeospheniscus and Palaeeudyptes. 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. Over 35 species and 26 families of fish, which includes sharks, have been described from the Ypresian Cucullaea bed.Mammals
Meriduingulata
; Astrapotheria| Taxa | Species | Locality | Stratigraphic position | Material | Notes | Images |
| Antarctodon | A. sobrali | Locality DVP 2/84 and IAA 1/90. | Cucullaea I allomember. | MLP 08-XI-30-1, an isolated right p4 or m1. | An astrapothere | |
| Trigonostylops | T. sp. | Cucullaea I allomember. | An astrapothere |
; Litopterna
| Taxa | Species | Locality | Stratigraphic position | Material | Notes | Images |
| Notiolofos | N. arquinotiensis | Locality IAA 1/13 and DPV 16/84. | Acantilados II, Campamento, Cucullaea I Allomember and Submeseta Member. | A Brachyodont lower right molar fragment, probably m1 or m2, preserves a portion of the talonid with most of the lingual side and left M3 incomplete. | A sparnotheriodontid litoptern. | |
| Notiolofos | N. regueroi | Locality IAA 2/16 | Lower coquina bed of Cucullaea I Allomember. | IAA-PV 173, Isolated complete left m3. | A sparnotheriodontid litoptern. | |
| Victorlemoinea | V. sp. | Cucullaea I allomember. | A sparnotheriodontid litoptern. |
Metatherians
; Derorhynchidae| Taxa | Species | Locality | Stratigraphic position | Material | Notes | Images |
| Derorhynchus | D. minutus | Locality IAA 1/90. | Allomember Cucullaea I. | MLP 96-1-5-44, incomplete right horizontal ramus of the dentary fragment with m2-3. | ||
| Pauladelphys | P. juanjoi | Locality IAA 2/95 and IAA 1/90. | Allomember Cucullaea I. | An isolated lower molar and an upper left molar. | - | |
| Xenostylos | X. peninsularis | Locality IAA 1/90. | Allomember Cucullaea I. | MLP 94-111-15-10, an isolated upper right molar. | - |
; Microbiotheria
| Taxa | Species | Locality | Stratigraphic position | Material | Notes | Images |
| Marambiotherium | M. glacialis | Locality IAA 1/90 and RV-8200. | Cucullaea I allomember. | 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. | A microbiothere, related to the modern monito del monte. | |
| Woodburnodon | W. casei | Locality IAA 1/95. | Cucullaea I allomember. | MLP 04-III-1-2, an isolated, worn upper right molar. | A microbiothere, related to the modern monito del monte. |
; Polydolopimorphia
| Taxa | Species | Locality | Stratigraphic position | Material | Notes | Images |
| Antarctodolops | A. dailyi | Locality IAA 2/95, DPV 2/84, and DPV 6/84. | Cucullaea I allomember. | UCR 20910, a left dentary with p3-m2. | A polydolopimorphian metatherian. | |
| Antarctodolops | A. mesetaense | Locality IAA 1/90 and DPV 6/84. | Cucullaea I allomember. | Right dentary fragments. | A polydolopimorphian metatherian. | |
| Perrodelphys | P. coquinense | Locality IAA 1/90. | Cucullaea I allomember. | MLP 96-1-5-11, an isolated left lower molar. | A polydolopimorphian metatherian. | |
| Polydolops | P. dailyi | Locality IAA 1/90 & DPV 3/84. | Cucullaea I allomember. | A polydolopimorphian metatherian. | ||
| Polydolops | P. seymouriensis | Locality IAA 1/90 & DPV 3/84. | Cucullaea I allomember. | A polydolopimorphian metatherian. | ||
| Polydolops | P. thomasi | Locality IAA 1/90 & DPV 3/84. | Cucullaea I allomember. | A polydolopimorphian metatherian. | ||
| Pujatodon | P. ektopos | Locality IAA 1/90. | Cucullaea I Allomember. | Specimen MLP 14-I-10-20, a lower left molar partially worn. | A polydolopimorphian metatherian. |