The López 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) to the Danian stage of the lower Paleocene, from about 70 to 65.5 million years ago, straddling the Cretaceous-Paleogene boundary.
Cretaceous-Paleogene boundary
The Cretaceous–Paleogene boundary (K–Pg) crops out on Seymour Island in the upper levels of the López de Bertodano Formation. 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. Directly above the boundary a layer of disarticulated fish fossils occurs, victims of a disturbed ecosystem immediately following the impact event. Multiple reports have described evidence for climatic changes in Antarctica prior to the mass extinction, 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.
Climate During the Maastrichtian, Seymour Island was located just outside the Antarctic polar circle at around ~64°S latitude. Studies on oxygen-18 isotopes found in belemnites and benthic foraminifera have calculated intermediate-deep-shelf water temperatures at an average of . This paper also suggested annual temperature variability of 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. Alternatively, a study using data acquired from ancient bacterial membrane lipids yielded a slightly warmer temperature of ; further research in other high latitude localities have suggested these methods may be biased towards summer temperatures. More recently a paper has used oxygen-18 isotopes from bony fish fossils to estimate an average water temperature of , overall supporting a subpolar climate regime perhaps similar to the modern Magallanes Region.
Fossil content The López de Bertodano Formation has provided many fossils of flora, dinosaurs and birds.Marambio Group - Lopez de Bertodano Formation at Fossilworks.orgSeymour Island Group - Lopez de Bertodano Formation at Fossilworks.orgUpper Lopez de Bertodano Formation at Fossilworks.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, 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, and cephalopods (ammonites and nautiloids).
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.
Vertebrates Dinosaurs
Ornithischians
Ornithischians recorded from López de Bertodano Formation Genus Species Member/location Material Description ImageElasmariaIndeterminateSandwich Bluff MemberCM 93790, right prox. Metatarsal II; Rt. Prox. Metatarsal IV; left. Prox. Fibula IndeterminateSandwich Bluff MemberMLP 98-I-10-70, pedal ungualAlso considered Ornithischia indet. Hadrosauridae Indeterminate Sandwich Bluff, Vega Island Isolated cheek tooth, MLP 98-I-10-1.The first hadrosaur remains known from AntarcticaIndeterminateSeymour IslandMLP 96-1-6-2, Distal end of metatarsalParankylosauriaIndeterminateSandwich Bluff MemberRight pedal ungual IV, CM93791, and osteoderm
Saurischians Saurischians recorded from López de Bertodano Formation Genus Species Member/location Material Description ImageAvesIndeterminateLower Sandwich BluffAMNH FARB 30898, incomplete coracoid Charadriiform Indeterminate Cape Lamb Partial skeleton; incomplete tarsometatarsus (MLP 98-I-10-25) Reminiscent of a thick-knee Conflicto C. antarcticus Seymour Island MLP 07-III-1-1, a three-dimensionally preserved, partly complete skeleton An anseriform GaviiformesIndeterminateVEG IAA 2/98, Isla VegaMLP 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.Very similar to that of Gavia immercf. GaviiformesIndeterminateVEG IAA 2/98, Isla VegaMLP 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 tibiotarsusVery similar to that of Gavia immerMegaraptoraIndeterminateSandwich Bluff, Cape LambSDSM 159537, maxilla Has oblong and narrow tooth alveoli, seen in megaraptoransIndeterminateSandwich Bluff, Cape LambSDSM 9918, left maxillaryOrnithuraeIndeterminateCape Lamb, Vega IslandAMNH FARB 30913, distal tarsometatarsus Polarornis P. gregorii Seymour Island Partial skull and skeleton, holotypeA possible vegaviid, or aequornithe P.? sp. Sandwich Bluff, Cape Lamb Partial skeleton including wing and hindlimbscf. P. gregoriiSandwich Bluff, Cape LambMN 7833-V, distal portion of a tarsometatarsusP. sp.IAA 10/13, Seymour IslandMLP 96-I-6-2, incomplete skeleton Pujatopouli P. soberana Seymour Island MLP-PV 08-XI-30-44, cranial and associated postcranial material An early aequornithe. Sauropoda? Indeterminate Tesore Hill Footprints? Potential sauropod footprints Theropoda Indeterminate Sandwich Bluff, Cape Lamb S061-9917, Fragments Indeterminate Tesore Hill Footprints? Potential theropod footprintsVegavisV. iaai Supporting informationLower Sandwich BluffHolotype (MLP 93-I-3-1), partial skeleton MACN-PV 19.748, partial skeletonA foot-propelled diver neognathV. geitononesosMolluscan Allomember, Marambio IslandMLP-PV 15-I-7-52. Skull lacking the upper beakA foot-propelled diver neognathV. notopothousaLower Sandwich BluffAMNH FARB 30899. Partial skullPreviously referred to V. iaai.V. sp.Plesiosaur Papoose, Cape LambIsolated femurInitially identified as a fossil of a member of Cariamae, but subsequently reinterpreted as a fossil of an unnamed large-bodied member of the genus Vegavis.cf. V. iaaiSandwich Bluff, Cape LambMN 7832-V, synsacrumVegaviidaeIndeterminateSeymour Island
Elasmosaurs Elasmosaurs recorded from López de Bertodano Formation Genus Species Member/location Material Description ImageAristonectesO'Gorman, J. P., Gasparini, Z., & Salgado, L. (2012). Postcranial morphology of Aristonectes (Plesiosauria, Elasmosauridae) from the Upper Cretaceous of Patagonia and Antarctica. Antarctic Science, 25(1), 71–82. https://doi.org/10.1017/S0954102012000673A. parvidens Seymour IslandPartial postcranial skeleton (MLP 89-III-3-1) A giant elasmosaurA. spSandwich Bluff, Cape LambMLP 11-I-1-15, caudal vertebraA. spSeymour IslandTTU.P.9219 (holotype skull and cervical vertebrae)ElasmosauridaeIndeterminateSW corner, Seymour IslandMLP 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 scapulaeIndeterminateSW corner, Seymour IslandZPAL R.8, pectoral, dorsal, and caudal vertebral centra, femur, tibia, and fragments of the humerus, scapula, and ischiaIndeterminateSeymour IslandTTU P 9240; dorsal, sacral and caudal vertebrae, limbs and paddle fragmentsIndeterminateSeymour IslandSGO.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.IndeterminateSeymour IslandTTU P 9238; part of cervicals, rib fragments, isolated paddles, and gastrolithsIndeterminateSeymour IslandTTU P 9239; isolated vertebrae, limb bones, paddle elements, and ribsIndeterminateSeymour IslandIAA 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 gastrolithsEuelasmosauridaIndeterminateSandwich Bluff, Cape LambCM 93780; left and right pubes and ischia: MLP 15-I-7-8, left ilium and indeterminate fragmentsMarambionectesM. molinaiSeymour IslandPartially 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 MorturneriaM. seymourensis Seymour Islandseveral cervical vertebrae, a right humerus, a nearly complete left forelimb missing the proximal end of the humerus, and a left femur (TTU P9217)An elasmosaurWeddellonectiaIndeterminateSandwich Bluff, Cape LambMLP 15-I-7-48, right humerus, ulna, ulnare, intermedium, distal carpal I, distal carpal II+III, pisiform, phalanges and one ribIndeterminateSeymour IslandMLP 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
Mosasaurs