Acritarch biostratigraphic and δ¹³C chemostratigraphic data from the Krol A Formation in the Solan area (Lesser Himalaya, northern India) are integrated to aid inter-basinal correlation of early–middle Ediacaran strata. We identified a prominent negative δ¹³C excursion (likely equivalent to EN2 in the lower Doushantuo Formation in the Yangtze Gorges area of South China), over a dozen species of acanthomorphs (including two new species—Cavaspina tiwariae Xiao n. sp., Dictyotidium grazhdankinii Xiao n. sp.), and numerous other microfossils from an interval in the Krol A Formation. Most microfossil taxa from the Krol A and the underlying Infra-Krol formations are also present in the Doushantuo Formation. Infra-Krol acanthomorphs support a correlation with the earliest Doushantuo biozone: the Appendisphaera grandis-Weissiella grandistella-Tianzhushania spinosa Assemblage Zone. Krol A microfossils indicate a correlation with the second or (more likely, when δ¹³C data are considered) the third biozone in the lower Doushantuo Formation (i.e., the Tanarium tuberosum-Schizofusa zangwenlongii or Tanarium conoideum-Cavaspina basiconica Assemblage Zone). The association of acanthomorphs with EN2 in the Krol Formation fills a critical gap in South China where chert nodules, and thus acanthomorphs, are rare in the EN2 interval. Like many other Ediacaran acanthomorphs assemblages, Krol A and Doushantuo acanthomorphs are distributed in low paleolatitudes, and they may represent a distinct paleobiogeographic province in east Gondwana. The Indian data affirm the stratigraphic significance of acanthomorphs and δ¹³C, clarify key issues of lower Ediacaran bio- and chemostratigraphic correlation, and strengthen the basis for the study of Ediacaran eukaryote evolution and paleobiogeography.

Two rare, phosphatized, tubular microfossils of uncertain affinity, probably algal, are described from the Portfjeld biota (Ediacaran) of North Greenland. Portfjeldia aestatis n. gen. n. sp. preserves two tubules, one of which branches, within an annulated outer sheath. Its morphology can be compared to that of the much larger Ramitubus from the Weng'an biota of South China. An unnamed long, parallel-sided tubule occupied the postmortal cavity formed within diagenetically mineralized specimens of the cyanobacterium Jiangispirellus.

The terminal Ediacaran Shibantan biota (∼550–543 Ma) from the Dengying Formation in the Yangtze Gorges area of South China represents one of the rare examples of carbonate-hosted Ediacara-type macrofossil assemblages. In addition to the numerically dominant taxa—the non-biomineralizing tubular fossil Wutubus and discoidal fossils Aspidella and Hiemalora, the Shibantan biota also bears a moderate diversity of frondose fossils, including Pteridinium, Rangea, Arborea, and Charnia. In this paper, we report two species of the rangeomorph genus Charnia, including the type species Charnia masoni Ford, 1958 emend. and Charnia gracilis new species, from the Shibantan biota. Most of the Shibantan Charnia specimens preserve only the petalodium, with a few bearing the holdfast and stem. Despite overall architectural similarities to other Charnia species, the Shibantan specimens of Charnia gracilis n. sp. are distinct in their relatively straight, slender, and more acutely angled first-order branches. They also show evidence that may support a two-stage growth model and a epibenthic sessile lifestyle. Charnia fossils described herein represent one of the youngest occurrences of this genus and extend its paleogeographic and stratigraphic distributions. Our discovery also highlights the notable diversity of the Shibantan biota, which contains examples of a wide range of Ediacaran morphogroups.

Large, soft-bodied fronds were among the first large and complex creatures that evolved on our planet, and these fronds dominated the seas during the latter half of the Ediacaran Period (575–538 million years ago), which immediately preceded the Cambrian. Some of the first Ediacaran fronds described were found in the Flinders Ranges of Australia. A frond named Rangea longa by Martin Glaessner and Mary Wade in 1966, which was nearly half a meter long, is unique in almost always appearing on the top of the bed that contains it. The morphologies of the specimens they described were variable, which hindered global understanding of how many types were present and the time range that each morphology exhibited. Our study of all specimens ever discovered shows that Glaessner and Wade were correct in concluding that all these specimens belonged to the same species, and superb preservation of these fronds shows that the variation we see among these fossils reflects which side of the frond faced up and what angle it lay on the sea floor when it died. These fronds represent a new genus called Akrophyllas (literally “the frond on the top” in ancient Greek). Akrophyllas lived as an erect frond that was firmly anchored to the shallow sea floor by a bulbous holdfast, and died when it was buried by sand during a storm.

Decimeter-scale, elongate, fossil fronds from the Ediacara Range in South Australia were formally described as Rangea longa Glaessner and Wade, 1966, but the disparate nature of documented specimens has hindered their inclusion in global syntheses and has resulted in these fossils being assigned to at least five different genera in two different clades since their discovery. Detailed study of the type material from the Ediacara Range and the few specimens subsequently collected elsewhere in the Flinders Ranges reaffirms that these specimens represent a single species, with the apparent morphological variation between specimens entirely taphonomic and reflecting the obverse and reverse surfaces of these fronds coupled with the orientation of the frond axis and petaloids at different angles relative to the sea bottom on which they were preserved. The preserved architecture of these fronds constitutes three orders of branching microstructure that are strictly orthogonal to immediately higher and lower orders. This implies affinities with the arboreomorphs, but representing a new frond genus herein named Akrophyllas. Akrophyllas n. gen. differs from all other Ediacaran fronds in exhibiting a stalk that is visible only on one side of the frond and is internal to the other side where the first-order branches instead meet at a zigzag axial trace. Akrophyllas n. gen. was attached to a bulbous holdfast on the sea bottom, and evidence for current scours that formed in the lee of the fronds and for a strong current alignment of felled fronds with depositional overlap of adjacent fronds imply an upright, epibenthic lifestyle for Akrophyllas longa new combination.

In the last ten million years before the Cambrian Explosion, groundbreaking early animals started to make shells. Fossils of these shells can be found worldwide, but making sense of how these animals might have been related and what their ecosystems looked like remain important questions. Here, we reevaluate shelly fossils that were first reported in the 1980s from northwestern Mexico in an effort to compare them to other reinvigorated and similar fossil deposits in the southwestern USA. Using a wide range of approaches, including standard microscopy, thin-section preparation, and electron and x-ray microscopy, we found that these Mexican shells: (1) represent multiple distinct groups of animals; (2) are preserved in a couple of different ways; (3) show signs that their shells might not have been overly rigid or inflexible; and (4) might also show indications that predators had punctured or drilled into their shells. Along with ongoing efforts elsewhere around the world, studies of the fossil record just before life's first large diversification event will help to provide a framework for global correlation and illuminate the earliest evolutionary and ecological dynamics of animals.

The terminal Ediacaran Period is signaled worldwide by the first appearance of skeletonizing tubular metazoan fossils, e.g., Cloudina Germs, 1972 and Sinotubulites Chen, Chen, and Qian, 1981. Although recent efforts have focused on evaluating the taxic composition and preservation of such assemblages from the southwestern United States, comparable forms reported in the 1980s from Mexico remain to be re-examined. Here, we reassess the latest Ediacaran skeletal materials from the La Ciénega Formation of the Caborca region in Sonora, Mexico, using a combination of analytical methods: optical microscopy of extracted fossils, thin-section petrography, scanning electron microscopy and energy dispersive X-ray spectroscopy, and X-ray tomographic microscopy. From our examination, we conclude that the La Ciénega hosts a polytaxic assemblage of latest Ediacaran tubular organisms that have been preserved through two taphonomic pathways: coarse silicification and calcareous recrystallization preserving finer details. Further, these fossils show signs that their shells might not have been inflexible or completely mineralized in vivo, and that they might also record tentatively interpreted predation traces in the form of drill holes or puncture marks. This work, along with ongoing efforts around the world, helps to provide a framework for biostratigraphic correlation and possible subdivision of the Ediacaran Period, and further shapes our view of metazoan evolution and ecology in the interval directly preceding the Cambrian explosion.

Seven species occur in shallow-marine limestone of the Sete Lagoas Formation, Bambuí Group, in Januária, Brazil, including Siphonophycus robustum, Leiosphaeridia crassa, Leiosphaeridia jacutica, Leiosphaeridia minutissima, Leiosphaeridia tenuissima, Germinosphaera bispinosa, and a new species named Ghoshia januarensis. In the lower part of the studied section, these occurrences are common, but only Ghoshia januarensis is found in the upper part. This is likely due to changes in the environment or preservation conditions. The Leiosphaeridia species, especially Leiosphaeridia minutissima, dominates the assemblage of organic-walled microfossils. While most described taxa have long stratigraphic ranges, they are consistent with a terminal Ediacaran age, as indicated by detrital zircon data and tubular fossils (e.g., Cloudina and Corumbella) from the Sete Lagoas Formation.

This work presents a detailed taxonomic study on organic-walled microfossils from the Ediacaran Sete Lagoas Formation (Bambuí Group) at the Barreiro section in the Januária area of the São Francisco basin, Brazil. Seven species are described, including Siphonophycus robustum (Schopf, 1968), Ghoshia januarensis new species, Leiosphaeridia crassa (Naumova, 1949), Leiosphaeridia jacutica (Timofeev, 1966), Leiosphaeridia minutissima (Naumova, 1949), Leiosphaeridia tenuissima Eisenack, 1958, and Germinosphaera bispinosa Mikhailova, 1986. These taxa are recovered for the first time in the Sete Lagoas Formation. They occur abundantly in the lower portion of the studied section, but only Ghoshia januarensis is present in the upper part of the studied section, probably due to environmental or taphonomic changes. Leiosphaeridia species, particularly Leiosphaeridia minutissima, dominate the organic-walled microfossil assemblage. Although most taxa described here have long stratigraphic ranges, they are consistent with a terminal Ediacaran age as inferred from detrital zircon data and tubular fossils (e.g., Cloudina and Corumbella) from the Sete Lagoas Formation.

The Weng'an Biota, found in the Doushantuo Formation in Guizhou Province, South China, is a remarkable fossil assemblage known for its well-preserved ancient life forms. These include small organisms called acritarchs, algae, and even embryo-like fossils. Among these, acritarchs, shaped like spiny spheres, have been essential for understanding the age and relationships of rocks from the Ediacaran Period. Previous studies mainly focused on larger spiny acritarchs, overlooking the smaller ones. In our study, we carefully examined over 500 thin sections and discovered a wealth of well-preserved small and medium-sized acritarchs. These tiny fossils, with diameters ranging 20–150 µm, help us understand the ancient ecosystems and how life evolved during this critical time in Earth's history. We identified several different species of small spiny acritarchs, e.g., Tanarium conoideum, Tanarium elegans, Mengeosphaera membranifera, Mengeosphaera minima, and Variomargosphaeridium gracile. Additionally, we found medium-sized acritarchs, e.g., Tanarium tuberosum and Weissiella cf. W. grandistella. These new findings provide important clues for correlating the rocks of the Doushantuo Formation in the Weng'an area with those in the Yangtze Gorges region. They also help us understand the evolution of acritarchs in different parts of the world, including Australia, Siberia, and the East European Platform.

The Weng'an Biota from the Ediacaran Doushantuo Formation in Guizhou Province, southwestern China, is known for its three-dimensionally phosphatized acritarchs, multicellular algae, and embryo-like animal fossils. Among these diverse microfossils, acanthomorphic acritarchs have played a significant role in the biostratigraphic subdivision and correlation of the lower-middle Ediacaran System. However, most previous studies on the biostratigraphy of the Doushantuo Formation in the Weng'an area have focused on large acanthomorphic acritarchs (LAAs, vesicle diameter >200 µm), whereas the smaller acanthomorphic acritarchs (SAAs, vesicle diameter <100 µm) from the Weng'an Biota have been largely overlooked. In this study, we examined >500 thin sections and discovered a large number of well-preserved, small (<100 µm) and medium-sized acanthomorphic acritarchs (MAAs, vesicle diameter ranging 100–200 µm). In total, we have identified SAAs in four genera and six species (Tanarium conoideum Kolosova, 1991, emend. Moczydłowska et al., 1993; Tanarium elegans Liu et al., 2014; Mengeosphaera membranifera Shang, Liu, and Moczydłowska, 2019; Mengeosphaera minima Liu et al., 2014; Estrella recta Liu and Moczydłowska, 2019; Variomargosphaeridium gracile Xiao et al., 2014), as well as two types of MAAs (Tanarium tuberosum Moczydłowska, Vidal, and Rudavskaya, 1993, emend. Moczydłowska, 2015; Weissiella cf. W. grandistella Vorob'eva, Sergeev, and Knoll, 2009, emend. Liu and Moczydłowska, 2019). This updated acritarch assemblage of the Weng'an Biota is valuable for correlating the Ediacaran Doushantuo Formation between the Weng'an and Yangtze Gorges areas. It also serves as a tool to test the proposed acritarch biozones in Ediacaran formations of South China and other localities, including Australia, Siberia, and the East European Platform.