Ari Iglesias

Premise: The modern distribution of the southern cypresses, Callitroideae (Cupressaceae), reflects a classic Gondwanan distribution. The initial diversification of Callitroideae is estimated to have occurred during the Cretaceous, yet fossils from this period are rare, hampering our understanding of its early evolutionary history. Methods: A permineralized cluster of callitroid seed cones has been recovered from the Late Cretaceous Santa Marta Formation on James Ross Island, Antarctica. The specimen was sectioned using the acetate peel technique. We conducted a comparative morphological and anatomical investigation of the fossil with living members of Callitroideae and tested its phylogenetic placement using Bayesian and parsimony inference methods. Results: Each cone has four opposite‐decussate ovuliferous complexes, a central columella, and subtending bifacially flattened shoots. This new fossil resembles living Austrocedrus in having ovuliferous complexes with a short, apically located bract tip and an abaxial row of vascular bundles. Phylogenetic reconstructions place the fossil sister to Austrocedrus chilensis , and we erect a new species, Austrocedrus vetus sp. nov. Conclusions: Austrocedrus is known by a handful of Cenozoic fossils from Australia and a single surviving taxon, A. chilensis , in the Southern Andes of Chile and Argentina. Austrocedrus vetus is the oldest evidence of the genus, extending its stratigraphic record by 40 Ma. Our findings indicate that Austrocedrus diverged by the Campanian and experienced stasis in seed cone morphology. Furthermore, this fossil is the first occurrence of Austrocedrus in Antarctica, demonstrating that the genus was an element of Antarctic forest ecosystems during the Late Cretaceous.

Summary: Through symbiotic associations with microbes, mosses play many important ecological roles in terrestrial ecosystems, such as facilitating trophic interactions and nitrogen cycling. However, little is known about interactions between mosses and microbes in past ecosystems. Here, we characterize a permineralized moss with epiphytic cyanobacteria and tubular hyphae from the Cretaceous of Antarctica. The fossil was identified in a calcium carbonate concretion from the Beta member of the Santa Marta Formation Cretaceous (Campanian) from James Ross Island. The fossil was studied using acetate peels and light microscopy. The fossil moss is assignable to Bryopsida. Cyanobacteria trichomes with heterocyst‐like cells are present in leaf axils and the perichaetium. In some leaf axils, epiphytic fungi are preserved. The apical perichaetium contains several archegonia; one contains an egg cell while another contains a possible embryo. Fossil epiphytic cyanobacteria demonstrate that moss associations were part of Antarctic polar forests during the Cretaceous. Recognizing their importance in modern ecosystems, moss–cyanobacteria associations likely contributed bioavailable nitrogen to the nutrient cycle of ancient polar forests, which would benefit organisms in different trophic levels. This work reveals long‐term stasis in commensal relationships between cyanobacteria and mosses and provides a minimum age for these relationships.

Premise: Palms can develop a wide variety of fruit shapes and sizes. Species in the Cocoseae tribe possess an evident synapomorphy: the presence of three “eyes” or germination pores in their endocarp, probably best known by the widespread monotypic extant Cocos nucifera . There is little consensus on the biogeographic history of the cocosoid palms, there being few previous world‐spread fossil records, some of which require further study in order to establish a clear taxonomic assignment. Methods: Anatomy of permineralized fruits (pyrenes) from the Miocene in northern Patagonia, Argentina, was studied using thin sectioning and polished surfaces observed under transmitted and epifluorescence microscopy. Some fossils were analyzed under X‐ray micro‐tomography. Results: We report a new palm fruit fossil record based on anatomical studies of >30 specimens. These were assigned to a new fossil taxon within the subtribe Attaleinae (Tribe Cocoseae, Arecoideae). Furthermore, the presence of an unusual character as endocarp intrusions suggests a close anatomical relationship with the extant Syagrus romanzoffiana . Conclusions: The new fossil taxon is one of the best‐preserved fossils of the Cocoseae worldwide and is the first unambiguous fossil record for Attaleinae from southern South America. The extremely high concentration (hundreds to thousands) of pyrenes within several strata of the basal section of the Chichinales Formation and their wide distribution in the study area allow for the interpretation of a palm grove community. This record represents the most austral occurrence of the Attaleinae in South America, indicating that subtropical climatic conditions extended into northern Patagonia almost to the Early Miocene.

Premise: The spurge family Euphorbiaceae is prominent in tropical rainforests worldwide, particularly in Asia. There is little consensus on the biogeographic origins of the family or its principal lineages. No confirmed spurge macrofossils have come from Gondwana.Methods: We describe the first Gondwanan macrofossils of Euphorbiaceae, represented by two infructescences and associated peltate leaves from the early Eocene (52 Myr ago [Ma]) Laguna del Hunco site in Chubut, Argentina.Results: The infructescences are panicles bearing tiny, pedicellate, spineless capsular fruits with two locules, two axile lenticular seeds, and two unbranched, plumose stigmas. The fossils' character combination only occurs today in some species of the Macaranga‐Mallotus clade (MMC; Euphorbiaceae), a widespread Old‐World understory group often thought to have tropical Asian origins. The associated leaves are consistent with extant Macaranga.Conclusions: The new fossils are the oldest known for the MMC, demonstrating its Gondwanan history and marking its divergence by at least 52 Ma. This discovery makes an Asian origin of the MMC unlikely because immense oceanic distances separated Asia and South America 52 Ma. The only other MMC reproductive fossils so far known are also from the southern hemisphere (early Miocene, southern New Zealand), far from the Asian tropics. The MMC, along with many other Gondwanan survivors, most likely entered Asia during the Neogene Sahul‐Sunda collision. Our discovery adds to a substantial series of well‐dated, well‐preserved fossils from one undersampled region, Patagonia, that have changed our understanding of plant biogeographic history.

The Snow Hill Island Formation (SHIF; late Campanian - early Maastrichtian) crops out in the northeast of the Antarctic Peninsula and constitutes the basal part of the late Campanian-early Maastrichtian sedimentary succession of the James Ross Basin (NG Sequence). Its major exposures occur at the James Ross and Vega islands. Several fossil-bearing localities have been identified in the SHIF providing a valuable fauna of invertebrates and vertebrates, and flora. Our study focuses on the vertebrate fauna recovered at Gamma and Cape Lamb members of the SHIF. The marine vertebrate assemblages include chondrichthyans, actinopterygians, and marine reptiles (elasmosaurid plesiosaurs and mosasaurs). A diverse terrestrial vertebrate assemblage has been reported being characterized by dinosaurs (sauropod, elasmarian ornithopods, nodosaurid ankylosaur, and a paravian theropod), pterosaurs and birds. Most SHIF dinosaurs share close affinities with penecontemporaneous taxa from southern South America, indicating that at least some continental vertebrates could disperse between southern South America and Antarctica during the Late Cretaceous. The Snow Hill Island Formation provides the most diverse Late Cretaceous marine and continental faunas from Antarctica. The present study summarizes previous and new vertebrate findings with the best actualized stratigraphical framework, providing a more complete fauna association and analyzing further perspectives.

Many plant genera in the tropical West Pacific are survivors from the paleo-rainforests of Gondwana. For example, the oldest fossils of the Malesian and Australasian coniferAgathis(Araucariaceae) come from the early Paleocene and possibly latest Cretaceous of Patagonia, Argentina (West Gondwana). However, it is unknown whether dependent ecological guilds or lineages of associated insects and fungi persisted on Gondwanan host plants likeAgathisthrough time and space. We report insect-feeding and fungal damage on PatagonianAgathisfossils from four latest Cretaceous to middle Eocene floras spanning ca. 18 Myr and compare it with damage on extantAgathis. Very similar damage was found on fossil and modernAgathis, including blotch mines representing the first known Cretaceous–Paleogene boundary crossing leaf-mine association, external foliage feeding, galls, possible armored scale insect (Diaspididae) covers, and a rust fungus (Pucciniales). The similar suite of damage, unique to fossil and extantAgathis, suggests persistence of ecological guilds and possibly the component communities associated withAgathissince the late Mesozoic, implying host tracking of the genus across major plate movements that led to survival at great distances. The living associations, mostly made by still-unknown culprits, point to previously unrecognized biodiversity and evolutionary history in threatened rainforest ecosystems.

The Cretaceous–Paleogene (K/Pg) extinction appears to have been geographically heterogeneous for some organismal groups. Southern Hemisphere K/Pg palynological records have shown lower extinction and faster recovery than in the Northern Hemisphere, but no comparable, well-constrained Southern Hemisphere macrofloras spanning this interval had been available. Here, macrofloral turnover patterns are addressed for the first time in the Southern Hemisphere, using more than 3500 dicot leaves from the latest Cretaceous (Maastrichtian) and the earliest Paleocene (Danian) of Argentine Patagonia. A maximum ca. 90% macrofloral extinction and ca. 45% drop in rarefied species richness is estimated across the K/Pg, consistent with substantial species-level extinction and previously observed extirpation of host-specialized leaf mines. However, prior palynological and taxonomic studies indicate low turnover of higher taxa and persistence of general floral composition in the same sections. High species extinction, decreased species richness, and homogeneous Danian macrofloras across time and facies resemble patterns often observed in North America, but there are several notable differences. When compared with boundary-spanning macrofloras at similar absolute paleolatitudes (ca. 50°S or 50°N) from the Williston Basin (WB) in the Dakotas, both Maastrichtian and Danian Patagonian species richnesses are higher, extending a history of elevated South American diversity into the Maastrichtian. Despite high species turnover, our analyses also reveal continuity and expansion of leaf morphospace, including an increase in lobed and toothed species unlike the Danian WB. Thus, both Patagonian and WB K/Pg macrofloras support a significant extinction event, but they may also reflect geographically heterogeneous diversity, extinction, and recovery patterns warranting future study.