Lopez de Bertodano Formation

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.[3] 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.[4] Directly above the boundary a layer of disarticulated fish fossils occurs, victims of a disturbed ecosystem immediately following the impact event.[3] Multiple reports have described evidence for climatic changes in Antarctica prior to the mass extinction,[5] 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.[6]

During the Maastrichtian, Seymour Island was located within the Antarctic polar circle at around ~65°S latitude.[7] Chemical studies on oxygen-18 isotopes found in shells and benthic foraminifera have calculated intermediate-depth and deep-sea ocean temperatures at a mean average of 6 °C (43 °F) with fluctuations of 4–12 °C (39–54 °F) 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.[8][9] Alternatively, a study using data acquired from ancient bacterial membrane lipids yielded a slightly warmer temperature of 12 ± 5 °C (54 ± 9 °F) around 66 Ma. Nevertheless, these estimated climates characterize primarily cool temperate environments with possible subpolar and warm episodes.[7]

The Lopez de Bertodano Formation has provided many fossils of flora, dinosaurs and birds.[10][11][12] Also the first fossil egg from Antarctica, Antarcticoolithus, was found in the formation.[13]

Dinosaur remains are among the fossils that have been recovered from the formation[14] 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,[15] and cephalopods (ammonites and nautiloids).[16]

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.[17]

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.

Dinosaurs recorded from Lopez de Bertodano Formation
Genus	Species	Member	Material	Description	Image
Polarornis	P. gregorii	Lower Sandwich Bluff	Partial skull and skeleton, holotype	A loon?[14]
	P.? sp.	Lower Sandwich Bluff	Partial skeleton including wing and hindlimbs	Possibly a more primitive form with strong flight ability and lighter bones
Vegavis	V. iaai[18]	Lower Sandwich Bluff	Partial skeleton, holotype	An anseriform
	V. sp.	Cape Lamb	Isolated femur	Initially identified as a fossil of a member of Cariamae,[19] but subsequently reinterpreted as a fossil of an unnamed large-bodied member of the genus Vegavis.[20]
Conflicto	C. antarcticus		Partial skeleton	An anseriform
Morrosaurus[21]	M. antarcticus			An elasmarian ornithopod
Undescribed charadriiform[22]	Unnamed species	Cape Lamb	Partial skeleton
Unidentified Neornithes	Unnamed species		Partial skull	Relationships undetermined, cranium some 5–6 centimetres (2.0–2.4 in) long
Undescribed hadrosaurid	Unnamed species		Isolated tooth[1]
Undescribed non-avian theropod	Unnamed species		Fragments[1]

Reptiles

Reptiles recorded from Lopez de Bertodano Formation
Genus	Species	Member	Material	Description	Image
Aristonectes[23]	A. cf. parvidens		Partial postcranial skeleton, MLP 89-III-3-1.	A giant elasmosaur
Kaikaifilu	K. hervei		Several incomplete parts of a skull, jawbone, 30 isolated teeth, and a partial left humerus.	A mosasaur.
Morturneria	M. seymourensis		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

• Lists of dinosaur-bearing stratigraphic units
• List of fossiliferous stratigraphic units in Antarctica
• South Polar region of the Cretaceous

• Poole, I.; Mennega, A. M. W.; Cantrill, D. J. (2003). "Valdivian ecosystems in the Late Cretaceous and Early Tertiary of Antarctica: further evidence from myrtaceous and eucryphiaceous fossil wood". Review of Palaeobotany and Palynology. 124 (1–2): 9–27. doi:10.1016/s0034-6667(02)00244-0. hdl:1874/31608. S2CID 129281012.