Lopez de Bertodano Formation

Lopez de Bertodano Formation
Stratigraphic range: Maastrichtian-Danian
~
TypeGeological formation
Unit ofMarambio & Seymour Island Groups
Sub-unitsCape Lamb & Lower Sandwich Bluff Members
UnderliesSobral Fm., La Meseta Fm.
OverliesSnow Hill Island Formation
Lithology
PrimarySiltstone, mudstone
OtherSandstone with concretions
Location
Coordinates64°00′S 57°24′W / 64.0°S 57.4°W / -64.0; -57.4
Approximate paleocoordinates61°54′S 68°06′W / 61.9°S 68.1°W / -61.9; -68.1
RegionSeymour Island, James Ross Island group, Vega Island
CountryAntarctica
Type section
Named forLópez de Bertodano Bay
Lopez de Bertodano Formation is located in Antarctica
Lopez de Bertodano Formation
Lopez de Bertodano Formation (Antarctica)

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[1]) to the Danian stage of the lower Paleocene, from about 70 to 65.5 million years ago, straddling the Cretaceous-Paleogene boundary.[2][3]

Cretaceous-Paleogene boundary

Geologic map of Seymour Island, Antarctica with the Lopez de Bertodano Formation in light green, the locations where the Cretaceous–Paleogene boundary is exposed are indicated

The Cretaceous–Paleogene boundary (K–Pg) crops out on Seymour Island in the upper levels of the Lopez de Bertodano Formation.[4] A small (but significant) iridium anomaly occurs at the boundary on Seymour Island, as at lower latitudes, thought to be fallout from the Chicxulub impactor in the Gulf of Mexico.[5] Directly above the boundary a layer of disarticulated fish fossils occurs, victims of a disturbed ecosystem immediately following the impact event.[4] Multiple reports have described evidence for climatic changes in Antarctica prior to the mass extinction,[6] but the extent to which these affected marine biodiversity is debated. Based on extensive marine fossil collections from Seymour Island, recent work has confirmed that a single and severe mass extinction event occurred at this time in Antarctica just as at lower latitudes.[7]

Climate

During the Maastrichtian, Seymour Island was located just outside the Antarctic polar circle at around ~64°S latitude.[8] Studies on oxygen-18 isotopes found in belemnites and benthic foraminifera have calculated intermediate-deep-shelf water temperatures at an average of 6 °C (43 °F).[9] This paper also suggested annual temperature variability of 5 °C (41 °F) based on Belemnite growth bands, perhaps in agreement with another study which has suggested that sea surface temperatures may have possibly dropped below freezing and formed sea ice at times.[10] Alternatively, a study using data acquired from ancient bacterial membrane lipids yielded a slightly warmer temperature of 12 ± 5 °C (54 ± 9 °F); further research in other high latitude localities have suggested these methods may be biased towards summer temperatures.[8][11] More recently a paper has used oxygen-18 isotopes from bony fish fossils to estimate an average water temperature of 6.8 °C (44.2 °F), overall supporting a subpolar climate regime perhaps similar to the modern Magallanes Region.[12]

Southern Chilean forests are a modern analogue for Maastrichtian Antarctica

Fossil content

The Lopez de Bertodano Formation has provided many fossils of flora, dinosaurs and birds.[13][14][15] Also the first fossil egg from Antarctica, Antarcticoolithus, was found in the formation.[16]

Dinosaur remains are among the fossils that have been recovered from the formation[17] and include at least two and probably as much as six lineages of indisputably modern birds: one related to waterfowl, a primitive shorebird or related form, 1 to 2 species of possible loons, a large and possibly flightless bird belonging to a lineage extinct today as well as a partial skull that might belong to either of the smaller species or represent yet another one. The formation also contains a rich fossil invertebrate fauna, including bivalves, gastropods,[18] and cephalopods (ammonites and nautiloids).[19]

The fish assemblage of the López de Bertodano Formation was dominated by Enchodus and ichthyodectiformes, accounting for 21.95% and 45.6% of local fish diversity respectively. Of the remaining percentages, sand sharks made up 10.5%, the cow shark Notidanodon 6.8%, chimaeras 3.9%, saw sharks 2.7%, various other teleost fish 2.4%, and the remaining 6% were shared between other sharks like Paraorthacodus, frilled sharks, Protosqualus, and Cretalamna.[20]

Vertebrates

Dinosaurs

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Ornithischians
Ornithischians recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Elasmaria Indeterminate Sandwich Bluff Member CM 93790, right prox. Metatarsal II; Rt. Prox. Metatarsal IV; left. Prox. Fibula [21]
Indeterminate Sandwich Bluff Member MLP 98-I-10-70, pedal ungual[21] Also considered Ornithischia Indet
Hadrosauridae Indeterminate Sandwich Bluff, Vega Island Isolated cheek tooth, MLP 98-I-10-1.[22][23] The 1st Hadrosaur remains of Antarctica
Indeterminate Seymour Island MLP 96-1-6-2, Distal end of metatarsal[24][23]
Parankylosauria Indeterminate Sandwich Bluff Member Right pedal ungual IV, CM93791, and osteoderm[21][23]
Saurischians
Saurischians recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Aves[25] Indeterminate Lower Sandwich Bluff AMNH FARB 30898, incomplete coracoid
Charadriiform[26] Indeterminate Cape Lamb Partial skeleton; incomplete tarsometatarsus (MLP 98-I-10-25)[27] Resembles Vanellus chilensis
Modern Vanellus chilensis, with convergent features
Conflicto[28] C. antarcticus Seymour Island MLP 07-III-1-1, a three-dimensionally preserved, partly complete skeleton An anseriform
Skeletal reconstruction
Gaviiformes Indeterminate VEG IAA 2/98, Isla Vega MLP 98-I-10-47, MLP 98-I-10-50, MLP 98-I-10-52, MLP 98-I-10-76: tarsometatarsus;MLP 98-I-10-59: diaphysis of left tibiotarsus; MLP 98-I-10-51: proximal end of left femur; MLP 98-I-10-48: distal end of left tibiotarsus; MLP 98-I-10-60 and MLP 98-I-10-61: distal end and partial corpus of pedal phalanges.[29] Very similar to that of Gavia immer
Modern Gavia immer, with convergent features
cf. Gaviiformes Indeterminate VEG IAA 2/98, Isla Vega MLP 98-I-10-54, MLP 98-I-10-27: tarsometatarsus; MLP 98-I-10-53: distal end of left tibiotarsus; MLP 98-I-10-49 distal end of right tibiotarsus[29] Very similar to that of Gavia immer
Megaraptora[21] Indeterminate Sandwich Bluff, Cape Lamb SDSM 159537, maxilla Has oblong and narrow tooth alveoli, seen in Megaraptorans
Indeterminate Sandwich Bluff, Cape Lamb SDSM 9918, left maxillary
Ornithurae[25] Indeterminate Cape Lamb, Vega Island AMNH FARB 30913, distal tarsometatarsus
Polarornis P. gregorii Sandwich Bluff, Seymour Island Partial skull and skeleton, holotype A Vegaviid of uncertain relative. Possibly a more primitive form with strong flight ability and lighter bones[17]
P.? sp. Sandwich Bluff, Cape Lamb Partial skeleton including wing and hindlimbs
cf. P. gregorii[27] Sandwich Bluff, Cape Lamb MN 7833-V, distal portion of a tarsometatarsus
P. sp. IAA 10/13, Marambio Island MLP 96-I-6-2, incomplete skeleton[29]
Sauropoda?[1][23] Indeterminate Tesore Hill Footprints? Potential Sauropod Footprints
Vegavis[30] V. iaai[31] Lower Sandwich Bluff
  • Holotype (MLP 93-I-3-1), partial skeleton
  • MACN-PV 19.748, partial skeleton
  • AMNH FARB 30899, skull[32]
 A foot-propelled diver anseriform
Vegavis restoration
V. sp. Plesiosaur Papoose, Cape Lamb Isolated femur Initially identified as a fossil of a member of Cariamae,[33] but subsequently reinterpreted as a fossil of an unnamed large-bodied member of the genus Vegavis.[34]
cf. V. iaai[27] Sandwich Bluff, Cape Lamb MN 7832-V, synsacrum
Vegaviidae Indeterminate Seymour Island [29]
Sphenisciformes?[25][35] Indeterminate Sandwich Bluff, Cape Lamb MLP-PV 08-XI-30-44, cranium and associated postcraneal material Relationships undetermined, cranium some 5–6 centimetres (2.0–2.4 in) long
Theropoda Indeterminate Sandwich Bluff, Cape Lamb S061-9917, Fragments[1][23]
Indeterminate Tesore Hill Footprints?[1][23] Potential Theropod Footprints

Fish

Bony fishes
Bony fish recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Antarctiberyx[36] A. seymouri Seymour Island TTU P9210. A poorly preserved anterior skull section with partial dentary attached A member of Beryciformes
Enchodus E. sp. Seymour Island One palatine tooth, MLP 12-XI-29-43; five teeth, MLP 12-XI-29-25 to 28; one tooth, MLP 12-XI-29-53; thirty-five teeth, MLP 12-XI-29-55; fifty-three teeth, MLP 12-XI-29-56[20] A member of Enchodontidae
Ichthyodectiformes Indeterminate Seymour Island One tooth, MLP 12-XI-29-21; ninety-four teeth, MLP 12-XI-29-38; thirteen teeth, MLP 12-XI-29-51; seventy-eight teeth, MLP 12-XI-29-52; one tooth, MLP 12-XI-29-54.[20]
Pachycormidae Indeterminate Seymour Island Isolated and fragmentary caudal fin-rays, MLP 13XI-29-57.[20]
Chondrichthyes
Chondrichthyes recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Callorhinchus C. sp. [37] Seymour Island Teeth A Chimaera
Carcharias cf. C. sp. Seymour Island Two left upper lateral teeth preserving one root branch and lateral denticle, MLP 13-XI-29-35, MLP 13-XI-29-37; one right upper lateral tooth preserving one root branch and lateral denticle, MLP 13-XI-29-36; several fragmentary teeth, MLP 13-XI29-4, MLP13-XI-29-44 to46, MLP13-XI-29-16, MLP 13-XI-29-13 to 14.[20] A Odontaspididae Shark
"Cretalamna" “C. appendiculata” Seymour Island One lateral lower tooth which lacks crown tip, distal lateral cusplet, and distal root branch, MLP 13XI-29-47; one anterior upper tooth lacking the distal root branch, distal lateral cusplet, and crown tip, MLP 13-XI-29-2[20] A Otodontidae Shark
Lamniformes Indeterminate Seymour Island Four crowns, MLP 13-XI-29-30.[20]
Notidanodon[36] N. sp. Seymour Island Teeth A Hexanchidae Shark
?N. sp.[37] Seymour Island Teeth A Hexanchidae Shark
Paraorthacodus P. sp. Seymour Island Four fragmentary teeth, MLP 13-XI-29-8, MLP 13XI-29-18, MLP 13-XI-29-31, and MLP 13-XI-29-32.[20] A Paraorthacodontidae Shark
Propristiophorus aff. P. sp. Seymour Island Three fragmentary rostral spines, MLP 13-XI-2939, MLP 13-XI-29-40, and MLP 13-XI-29-41.[20] A Pristiophoridae Shark
Protosqualus P. sp. Seymour Island Two lateral, almost complete teeth, MLP 13-XI29-9, MLP 13-XI-29-33; one latero-posterior, complete tooth, MLP 13-XI-29-10[20] A Squalidae Shark
Sphenodus[36] S. sp. Seymour Island Teeth A Orthacodontidae Shark
S. sp. Seymour Island Two fragmentary teeth, MLP 13-XI-29-20, MLP 13-XI-29-11[20] A Orthacodontidae Shark
Xampylodon[38] X. diastemacron Filo Negro Section, Klb 9 MN 7825-V (holotype),incomplete posterolateral tooth of the lower jaw, with only its anterior portion still preserved A Hexanchidae Shark


Elasmosaurs

Elasmosaurs recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Aristonectes[39] A. parvidens Seymour Island Partial postcranial skeleton (MLP 89-III-3-1) A giant elasmosaur
A. sp[40] Sandwich Bluff, Cape Lamb MLP 11-I-1-15, caudal vertebra
A. sp[41][42] Seymour Island TTU.P.9219 (holotype skull and cervical vertebrae)
Elasmosauridae[43] Indeterminate SW corner, Seymour Island MLP 82-I-28-1, an incomplete skeleton comprising 15 cervical, three pectorals, 21 dorsal, three sacral, and 22 caudal vertebrae, an almost complete left hind limb, some dorsal ribs, incomplete coracoids and fragments of the scapulae
Indeterminate[44] SW corner, Seymour Island ZPAL R.8, pectoral, dorsal, and caudal vertebral centra, femur, tibia, and fragments of the humerus, scapula, and ischia
Indeterminate[45] Seymour Island TTU P 9240; dorsal, sacral and caudal vertebrae, limbs and paddle fragments
Indeterminate[46] Seymour Island SGO.PV.6523, postcranial remains of a single adult individual, including remains of 9 mid-to-posterior cervical vertebrae (6 of them preserving parts of their centra), the right scapula, several fragments of ribs and gastralia, and one phalanx.
Indeterminate[45] Seymour Island TTU P 9238; part of cervicals, rib fragments, isolated paddles, and gastroliths
Indeterminate[41] Seymour Island TTU P 9239; isolated vertebrae, limb bones, paddle elements, and ribs
Indeterminate Seymour Island IAA Pv 443, an incomplete skeleton comprising the mandibular symphysis and part of right and left mandibular rami, cervical and dorsal centra, an incomplete humerus, radius, ulna, ulnare, intermedium, radiale and distal carpal 1, 2 þ 3 and 4, other fragmentary postcranial bones and associated gastroliths[47]
Euelasmosaurida[40] Indeterminate Sandwich Bluff, Cape Lamb CM 93780; left and right pubes and ischia: MLP 15-I-7-8, left ilium and indeterminate fragments
Marambionectes[48] M. molinai Seymour Island Partially articulated incomplete skeleton including cranial material, many vertebrae, ribs, an ilium, limb bones (right humerus and ulna, a femur), and gastroliths (IAA-Pv 752) A weddellonectian elasmosaur
Morturneria[41] M. seymourensis Seymour Island several cervical vertebrae, a right humerus, a nearly complete left forelimb missing the proximal end of the humerus, and a left femur (TTU P9217) An elasmosaur
Weddellonectia[49] Indeterminate Sandwich Bluff, Cape Lamb MLP 15-I-7-48, right humerus, ulna, ulnare, intermedium, distal carpal I, distal carpal II+III, pisiform, phalanges and one rib
Indeterminate Seymour Island MLP 14-I-20-16, 12 cervical vertebrae, three pectoral vertebrae, 11 dorsal vertebrae, one sacral vertebra, 11 caudal vertebrae, right femur, tibia, fibula and mesopodial elements, fragments of pectoral and pelvic girdles and gastroliths[49]

Mosasaurs

Mosasaurs recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Antarcticoolithus A. bradyi Seymour Island. A fossilized eggshell. A mosasaur.
Kaikaifilu[50] K. hervei Seymour Island Several incomplete parts of a skull, jawbone, 30 isolated teeth, and a partial left humerus (SGO.PV.6509) A tylosaurine mosasaur
Liodon[51] L sp. Vega Island Sandwich Bluff MLP 98-I-10-1 is a fragment of a maxilla; MLP 98-I-10-12/15/23 are a teeth[51] A Mosasauridae mosasaur
L sp. Seymour Island DJ.952.266, a tooth[52]
Mosasauridae Indeterminate Bahía Fósiles MLP 80-I-1-1, a cervical vertebra; MLP 80-I-1-2, a mandibular fragment; MLP 80-I-1-3, a cranial fragment; MLP 82-I-28-2, a vertebra; MLP 82-I-3-1/4, four caudal centers[53]
Indeterminate Seymour Island DJ.957.133, 18 partially articulated caudal vertebrae, four of which possess transverse process, and DJ.957.505 a caudal vertebra[52]
Indeterminate Filo Negro Section MLP 82-I-26-1, a pygal vertebra[38]
Indeterminate Seymour Island IAA-Pv 819, an almost complete right humerus.[54]
Indeterminate Seymour Island MLP 82-I-5-1, fragments of vertebrae and ribs[53]
Mosasaurus aff. M. hoffmanni Seymour Island DJ.1053.10, a large, fragmentary skull[52] A Mosasauridae mosasaur
M. sp. Seymour Island DJ.1020.2-A, DJ.1020.2-B and DJ.1053.14- A, teeth; MLP 83-X-12-2, a caudal vertebra; MLP 92-XII-30, skull fragments including one tooth and a relatively short, and medially constricted suprastapedial process of the quadrate[52]
M. sp. Seymour Island MLP 15-I-24-41, a partial skull including, partial frontal, right postorbital, parietal, right quadrate, right posterior end of basisphenoid, right coronoid, right angular, splenial and right surangular, a broken marginal tooth and several pterygoid teeth have been associated to this specimen.[55]
Plioplatecarpus P. sp. Seymour Island DJ.1020.2-C, DJ.1020.2-H and DJ.952.266, teeth[52] A Mosasauridae mosasaur
P. sp. Quebrada de la Foca muerta MLP 79-I-1/20, several vertebrae[53]
Tylosaurinae Indeterminate Bahía Fósiles MLP 87-II-7-1, a vertebra; MLP 86-X-28-7, an anterior caudal vertebra[53]
Indeterminate Seymour Island DJ.956.41, two or three caudal vertebrae[52]
Indeterminate Filo Negro Section lam. II, 7-8, a vertebra[38]

Other fossils

Ammonites[19]
Ammonites recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Diplomoceras D. cylindraceum A paperclip-shaped Ammonite.
Gaudryceras G. seymouriense
Grossouvrites G. joharae
Kitchinites K. laurae
Maorites M. densicostatus
Pachydiscus P. (Pachydiscus) ultimus
Pseudophyllites P. cf. loryi
Zelandites Z. varuna
Other invertebrates
Invertebrates recorded from Lopez de Bertodano Formation
Genus Species Member/location Material Description Image
Eutrephoceras E. dorbignyanum
Cyathocidaris C. nordenskjoldi
C. patera
Rotularia R. fallax

Flora

The Maastrichtian represented a period of Coolhouse conditions following the gradual global cooling from the Cretaceous Thermal Maximum. Coincident with this trend, an overturning of the Antarctic floral composition occurred during this time, particularly with the diversification of Nothofagaceae and the disappearance of some more archaic angiosperm forms. Other important constituents of the Antarctic floral communities include; Araucariaceae, Podocarpaceae, Atherospermataceae, Myrtaceae, Proteaceae, and Cunoniaceae. Fossil wood and sparse leaves indicates a canopy dominated by Nothofagus, whose wood anatomy suggested a rainforest climate as well as a transition towards deciduousness. Tree rings in Maastrichtian fossil wood are significantly narrower and more distinct than the preceding Coniacian-Campanian periods, indicating less productive growing conditions, and among fossil forests recorded in Antarctica, the Maastrichtian recorded the highest frequency of deferred optimum vessel diameter tree rings which occur when growth commences due to ample moisture availability but temperatures are below the required threshold for peak transpiration. This scenario is common among Nothofagus growing at ca. 55°S today.[56] One study using fossil wood characters calculated mean annual temperatures between 7.3–9.94 °C (45.14–49.89 °F), overall supporting a cool temperate climate for the Maastrichtian Antarctic Peninsula.[57]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Taxa Species Locality Material Notes Images
Antarctoxylon A. juglandoides Tentatively compared to Juglans.[58]
Araucaria A. antarctica Fossil leaves similar to the extant Araucaria araucana.[59]
A. fibrosa
Araucarioxylon A. sp. An Araucariaceaous wood morphotaxon.[56]
Atherospermoxylon A. sp. An Atherospermataceaous wood morphotaxon.[56]
Eucryphiaceoxylon E. eucryphioides A Eucryphiaceous wood morphotaxon.[58]
Laurelites L. jamesrossii An Atherospermataceaous wood morphotaxon. Similar to Laureliopsis.[56]
Myrceugenelloxylon M. antarcticus A Myrtaceaous wood morphotaxon. Similar to Myrceugenia.[58]
Nothofagus N. sp. Identical to leaves found in the Snow Hill Island Formation.[60]
Nothofagoxylon N. scalariforme A Nothofagaceaous wood morphotaxon, Subgenus Nothofagus.[61]
N. corrugatus A Nothofagaceaous wood morphotaxon, Subgenus Fuscospora.[61]
N. aconcaguaense A Nothofagaceaous wood morphotaxon, Subgenus Lophozonia.[61]
N. ruei A Nothofagaceaous wood morphotaxon, Subgenus Lophozonia.[61]
N. kraeuseli A Nothofagaceaous wood morphotaxon, Subgenus Lophozonia or Fuscospora.[61]
Phyllocladoxylon P. sp. A Podocarpaceaous wood morphotaxon.[56]
Podocarpoxylon P. sp. A Podocarpaceous wood morphotaxon.[56]
Sassafrasoxylon S. sp. Tentatively compared to Sassafras.[62]

See also

References

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  2. ^ Bowman, V.; Ineson, J.; Riding, J.; Crame, J.; Francis, J.; Condon, D.; Whittle, R.; Ferraccioli, F. (2016). "The Paleocene of Antarctica: Dinoflagellate cyst biostratigraphy, chronostratigraphy and implications for the palaeo-Pacific margin of Gondwana". Gondwana Research. 38: 132–148. Bibcode:2016GondR..38..132B. doi:10.1016/j.gr.2015.10.018.
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  13. ^ Marambio Group - Lopez de Bertodano Formation at Fossilworks.org
  14. ^ Seymour Island Group - Lopez de Bertodano Formation at Fossilworks.org
  15. ^ Upper Lopez de Bertodano Formation at Fossilworks.org
  16. ^ Legendre et al., 2020
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