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.
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. 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
Color key
Notes Uncertain or tentative taxa are in small text ; crossed out taxa are discredited.
Meriduingulata
Astrapotheria
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 (Telm 4) and Submeseta Member (Telm 7).
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).
A sparnotheriodontid litoptern .
N. regueroi
Locality IAA 2/16
Lower coquina bed of Cucullaea I Allomember.
IAA-PV 173, Isolated complete left m3.
Victorlemoinea
V. sp.
Cucullaea I allomember (Telm 5).
A sparnotheriodontid litoptern .
Cetacean
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Basilosaurus
undetermined
Llanocetus
L. denticrenatus
Locality DPV 10/84 and DVP 13/24.
Unit III Member and Telm 7.
A partial mandible with two teeth (specimen USNM 183022) and an endocast of the braincase.
a toothed baleen whale.
Zygorhiza
undetermined
Metatherians
Derorhynchidae
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Derorhynchus
D. minutus
Locality IAA 1/90.
Allomember Cucullaea I (Telm 5).
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 (Telm 5).
An isolated lower molar (MLP 95-1-10-2) and an upper left molar (MLP 96-1-5-44).
Xenostylos
X. peninsularis
Locality IAA 1/90.
Allomember Cucullaea I (Telm 5).
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 (Telm 5).
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.
Members of Microbiotheria
Woodburnodon
W. casei
Locality IAA 1/95.
Cucullaea I allomember (Telm 5).
MLP 04-III-1-2, an isolated, worn upper right molar (M2 or M3).
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 (Telm 5).
UCR 20910, a left dentary with p3-m2.
A polydolopimorphian metatherian.
A. mesetaense
Locality IAA 1/90 and DPV 6/84.
Cucullaea I allomember (Telm 5).
Right dentary fragments.
Perrodelphys
P. coquinense
Locality IAA 1/90.
Cucullaea I allomember (Telm 5).
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 (Telm 5).
A polydolopimorphian metatherian.
P. seymouriensis
Locality IAA 1/90 & DPV 3/84.
Cucullaea I allomember (Telm 5).
P. thomasi
Locality IAA 1/90 & DPV 3/84.
Cucullaea I allomember (Telm 5).
Pujatodon
P. ektopos
Locality IAA 1/90.
Cucullaea I Allomember (Telm 5).
Specimen MLP 14-I-10-20, a lower left molar (m2 or m3) partially worn.
A polydolopimorphian metatherian.
Other mammals
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Sudamerica
S. ameghinoi
Locality IAA 1/90 upper level.
Cucullaea I Allomember.
MLP 95-I-10-5, anterior part of a left dentary with the rodent-like incisor partially preserved.
A gondwanathere
Meridiolestida ?
Indeterminate
Locality IAA 1/90 upper level.
Cucullaea I Allomember.
A single tooth, now lost.
Xenarthra ?
Indeterminate.
Locality S124.
Cucullaea I Allomember/ Telm 4.
TMM 44190-1, left metacarpal II and A phalanx and a partial tooth
Birds
Sphenisciformes
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Anthropornis
A. grandis
Locality IAA 4/12, IAA 1/90, DPV 13/84, and DVP 2/84.
Telm 4 member, Telm 7 member, and Submeseta Allomember.
Humerus: MLP 93-X-1-4 (proximal epiphysis), MLP 82-IV-23-4 (proximal epiphysis), MLP 83-I-1-190(proximal epiphysis) and MLP 88-I-1-463(proximal epiphysis).
A. nordenskjoldi
Submeseta Allomember.
Humerus: MLP CX-60-25 (proximal epiphysis), MLP 83-V-30-5 (diaphysis) and MLP 93-X-1-104(complete humerus).
Archaeospheniscus
A. lopdelli
Submeseta Allomember.
A. wimani
Submeseta Allomember.
Delphinornis
D. arctowskii
DPV 14/84
Cucullaea I Allomember (Telm 7).
D. graclis
DPV 14/84
Cucullaea I Allomember (Telm 7).
D. larseni
DPV 13/84 and DPV 14/84.
Cucullaea I Allomember (Telm 5 and Telm 7) and Submeseta Allomember.
Marambiornis
M. exilis
Mesetaornis
M. polaris
Orthopteryx
O. gigas
Palaeeudyptes
P. antarcticus
Cucullaea I Allomember (Telm 3, Telm 4, Telm 5, and Telm 7) and Submeseta Allomember.
The narrow-flippered penguin.
P. gunnari
DVP 2/84, DVP 10/84, DVP 13/84, DVP 14/84, DVP 15/84, and ZPAL 4.
Cucullaea I Allomember (Telm 3, Telm 5, and Telm 7) and Submeseta Allomember.
P. klekowskii
DVP 2/84, DVP 10/84, DVP 13/84, DVP 14/84, DVP 16/84, and ZPAL 4.
Cucullaea I Allomember (Telm 3, Telm 5, and Telm 7) and Submeseta Allomember.
Wimanornis
W. seymourensis
DPV 14/84.
Cucullaea I Allomember (Telm 7) and Submeseta Allomember.
Tonniornis
T. mesetaensis
DPV 14/84.
Cucullaea I Allomember (Telm 7) and Submeseta Allomember.
T. minimum
DPV 14/84.
Cucullaea I Allomember (Telm 7) and Submeseta Allomember.
Pelagornithidae
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Dasornis
D. sp.
Amphibians
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Calyptocephalella
C. sp.
Locality IAA 2/95.
Cucullaea I Allomember (Telm 5).
The fragmentary right ilium (NRM-PZ B282) and a skull bone (NRM-PZ B281).
Calyptocephalellid frog
Fish
Chondrichthyes
Carcharhinidae
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Scoliodon
S. sp.
Hexanchidae
Lamnidae
Mitsukurinidae
Odontaspididae
Orectolobidae
Pristiophoridae
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Pristiophorus
P. lanceolatus
P. laevis
Squalidae
Actinopterygii
Xiphiidae
Notothenioids
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Mesetaichthys
M. jerzmanskae
An early member of the Notothenioidei , the dominant marine fish of Antarctica today. Initially assigned to the Gadiformes .
Cephalopods
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Antarcticeras
A. nordenskjoeldi
NRM 8, below IAA 1/90 (Ungulate Site).
Cucullaea I shell bed, Telm 4.
A fragmentary preserved straight shell.
An enigmatic cephalopod that is either considered a descendant of the orthocerids or an oegopsid squid.
Euciphoceras
E . sp.
NRM 8, below IAA 1/90 (Ungulate Site).
Cucullaea I shell bed, Telm 4.
A fragmentary preserved straight shell.
A nautiloid .
Plants
Taxa
Species
Locality
Stratigraphic position
Material
Notes
Images
Agathoxylon
A. pseudoparenchymatosum
fossilized seed of Notonuphar
Cupressinoxylon
C. hallei
Notonuphar
N. antarctica
IAA 2/95.
Cucullaea I Allomember (Telm 5).
Fossilized seeds.
A water lily.
Nelumbo
? Nelumbo sp.
Protophyllocladoxylon
P. francisiae
Phyllocladoxylon
P. antarcticum
P. pooleae
See also