The Lopez de Bertodano Formation is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

in the James Ross archipelago of the

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

. The strata date from the end of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

(upper-lower

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interv ...

stage) to the

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Creta ...

stage of the lower

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

, from about 70 to 65.5 million years ago, straddling the Cretaceous-Paleogene boundary.

Cretaceous-Paleogene boundary

Geologic map of Seymour Island, Antarctica

The

Cretaceous–Paleogene boundary The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end ...

(K–Pg) crops out 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 ...

in the upper levels of the Lopez de Bertodano Formation. A small (but significant)

iridium Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...

anomaly occurs at the boundary on Seymour Island, as at lower latitudes, thought to be fallout from the

Chicxulub impactor The Chicxulub crater () is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore near the community of Chicxulub, after which it is named. It was formed slightly over 66 million years ago when a large a ...

in the

Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United S ...

. Directly above the boundary a layer of disarticulated fish

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s occurs, victims of a disturbed ecosystem immediately following the impact event. Multiple reports have described evidence for climatic changes in

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 co ...

prior to the

mass extinction An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. I ...

, but the extent to which these affected marine

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic ('' genetic variability''), species ('' species diversity''), and ecosystem ('' ecosystem diversity' ...

is debated. Based on extensive marine fossil collections from Seymour Island, recent work has confirmed that a single and severe

event occurred at this time in Antarctica just as at lower latitudes.

Climate

During the Maastrichtian, Seymour Island was located within the Antarctic

polar circle A polar circle is a geographic term for a conditional circular line (arc) referring either to the Arctic Circle or the Antarctic Circle. These are two of the keynote circles of latitude (parallels). On Earth, the Arctic Circle is currently ...

at around ~65°S latitude. Chemical studies on

oxygen-18 Oxygen-18 (, Ω) is a natural, stable isotope of oxygen and one of the environmental isotopes. is an important precursor for the production of fluorodeoxyglucose (FDG) used in positron emission tomography (PET). Generally, in the radiopharm ...

isotopes found in shells and benthic

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

have calculated intermediate-depth and deep-sea ocean temperatures at a mean average of with fluctuations of throughout the Maastrichtian; one of the same studies has also suggested that sea surface temperatures may have been colder, possibly dropping below freezing and forming sea ice at times. Alternatively, a study using data acquired from ancient bacterial membrane lipids yielded a slightly warmer temperature of around 66 Ma. Nevertheless, these estimated climates characterize primarily cool temperate environments with possible subpolar and warm episodes.

Fossil content

The Lopez de Bertodano Formation has provided many fossils of

flora Flora (: floras or florae) is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. The corresponding term for animals is ''fauna'', and for f ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s and

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s.Marambio Group - Lopez de Bertodano Formation
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.orgSeymour Island Group - Lopez de Bertodano Formation
at

.orgUpper Lopez de Bertodano Formation
at

.org Also the first fossil egg from Antarctica, '' Antarcticoolithus'', was found in the formation.Legendre et al., 2020 Dinosaur remains are among the fossils that have been recovered from the formationWeishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, Antarctica)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. p. 606. . and include at least two and probably as much as six lineages of indisputably modern birds: one related to

waterfowl Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which i ...

, a primitive

shorebird 245px, A flock of Red_knot.html" ;"title="Dunlins and Red knot">Dunlins and Red knots Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflats in order to foraging, ...

or related form, 1 to 2 species of possible

loon Loons (North American English) or divers ( British / Irish English) are a group of aquatic birds found in much of North America and northern Eurasia. All living species of loons are members of the genus ''Gavia'', family Gaviidae and order G ...

s, a large and possibly

flightless bird Flightless birds are birds that through evolution lost the ability to fly. There are over 60 extant species, including the well known ratites (ostriches, emu, cassowaries, rheas, and kiwi) and penguins. The smallest flightless bird is the ...

belonging to a lineage extinct today as well as a partial

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, t ...

that might belong to either of the smaller species or represent yet another one. The formation also contains a rich fossil

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

fauna, including

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...

s, gastropods, and

cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, ...

s (

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttle ...

s and

nautiloid Nautiloids are a group of marine cephalopods ( Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and '' Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded speci ...

s). 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 ''Notidanodon'' is an extinct genus of cow shark. Fossils ascribed to this genus are known from the Jurassic, Cretaceous, and Paleogene periods. The genus is known from every continent including Antarctica. Species The earliest occurrences of ...

'' 6.8%,

chimaera Chimaeras are cartilaginous fish in the order Chimaeriformes , known informally as ghost sharks, rat fish, spookfish, or rabbit fish; the last three names are not to be confused with rattails, Opisthoproctidae, or Siganidae, respectively. A ...

s 3.9%, saw sharks 2.7%, various other

teleost fish Teleostei (; Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts ), is, by far, the largest infraclass in the class Actinopterygii, the ray-finned fishes, containing 96% of all extant species of fish. Tele ...

2.4%, and the remaining 6% were shared between other sharks like ''

Paraorthacodus ''Paraorthacodus'' is an extinct genus of cartilaginous fish. An unidentified species has been found in the Hasle Formation of Bornholm Bornholm () is a Danish island in the Baltic Sea, to the east of the rest of Denmark, south of Sweden, no ...

'',

frilled sharks ''Chlamydoselachus'' is a genus of sharks and the sole extant member of the family Chlamydoselachidae, in the order Hexanchiformes. It contains two extant and several extinct species. The most widely known species still surviving is the frill ...

, ''

Protosqualus ''Protosqualus'' ("Primitive Squalus") was a genus of Squalidae, dogfish shark that existed during the Cretaceous. Fossils have been found in Europe (mainly in France, Russia, Germany, Lithuania, The United Kingdom and Ukraine), East Asia (mainl ...

'', and ''Cretalamna''.

Other fossils

Among others, the following fossils have been found in the formation: ;Ammonites * '' Diplomoceras cylindraceum'' * '' Gaudryceras seymouriense'' * '' Grossouvrites joharae'' * '' Kitchinites laurae'' * '' Maorites densicostatus'' * '' Pachydiscus (Pachydiscus) ultimus'' * '' Zelandites varuna'' * '' Pseudophyllites cf. loryi'' ;Other invertebrates * '' Eutrephoceras dorbignyanum'' * '' Rotularia fallax'' * '' Cyathocidaris nordenskjoldi'', '' C. patera'' ;Flora * '' Antarctoxylon juglandoides'' * '' Eucryphiaceoxylon eucryphioides'' * '' Myrceugenelloxylon antarcticus'' *

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

Cretaceous-Paleogene boundary

Climate

Fossil content

Other fossils

See also

References

Bibliography

Further reading