The Eocene cetacean genera Andrewsiphius and Kutchicetus are systematically revised, their anatomy described, and their phylogenetic position analyzed. Each genus contains a single species, A. sloani and K minimus, and both are known only from the middle Eocene of the Indian Subcontinent. Andrewsiphius and Kutchicetus differ in a number of respects, the most important dental difference being that P2, P3, p2, and p3 are double-rooted in Andrewsiphius and single-rooted in Kutchicetus. Lower molars are separated by diastemata in Kutchicetus, but not in Andrewsiphius. Postcranially, Andrewsiphius has caudal vertebrae that are far more robust than those of Kutchicetus.

We propose the new clade Andrewsiphiinae for these two genera, based on their unique characters: the extremely slender jaw, fused mandibular symphysis, narrow palate and rostrum, and lower molars that have a low crown with three cusps lined up rostro-caudally. A phylogenetic analysis indicates that andrewsiphiines are either a subfamily of Remingtonocetidae or an independent branch on the Eocene cetacean lineage. Interpreting conservatively, we classify them as remingtonocetids. Andrewsiphiines have a long, robust, dorso-ventrally flattened tail and short limbs, suggesting that they swam using dorsoventral undulation of the tail.

New collections of trilobites from the type section of the Parahio Formation in the Parahio Valley, Spiti, and from the Parahio, Karsha, and Kurgiakh formations in the Zanskar Valley, permit biozonation based on material precisely located within measured stratigraphic sections. Specimens preserved in limestone with mild tectonic deformation clarify the features of several Himalayan taxa known previously only from severely deformed specimens preserved in shale. A total of 75 trilobite taxa from the Cambrian of Spiti and Zanskar can be referred, questionably at least, at the generic level or below, and 61 of these are present in our new collections. This new material is assigned with confidence to 29 existing species, and to 12 new species. Three new genera, Haydenaspis, Bhargavia, and Himalisania, are established; new species include Haydenaspis parvatya, Prozacanthoides lahiri, Probowmania bhatti, Xingrenaspis parthiva, X. shyamalae, Bhargavia prakritika, Kaotaia prachina, Gunnia smithi, Sudanamonocarina sinindica, Proasaphiscus simoni, Koldinia odelli, and Torifera jelli. Ten additional Himalayan forms are assigned at the generic level only, and another 11 are questionably assigned to genera or species. The zonation proposed includes 6 zones and 3 levels, including the Haydenaspis parvatya level, the Oryctocephalus indicus level, the Kaotaia prachina Zone, the Paramecephalus defossus Zone, the Oryctocephalus salteri Zone, the Iranoleesia butes level, the Sudanomocarina sinindica Zone, the Lejopyge acantha Zone, and the Proagnostus bulbus Zone. The sections span from the upper part of the informal Stage 4, Series 2 of the Cambrian System, about 511 Ma old, to the Proagnostus bulbus zone of the Guzhangian Stage near the top of Series 3, dated at about 501 Ma. This time interval is represented by about 2000 m of section, which is thick compared to similar intervals elsewhere and is consistent with high rates of sedimentation along the Himalayan margin at the time. The fauna resembles others from equatorial peri-Gondwanaland, with closest similarity to that of South China. It also bears strong affinity to the North China fauna. Juvenile trilobites are described for the first time from India. A new Chinese species, Monanocephalus liquani, is also described.

The Kel'tminskaya-1 borehole, drilled along the northeastern margin of the East European Platform (EEP), reveals some 3,600 m of Neoproterozoic sedimentary rocks, mostly confined to the subsurface. The upper 1,000 m of the drilled section correlates with late Ediacaran Redkino and Kotlin successions on the EEP, whereas the lowermost 2,000 m can be related to pre-Sturtian (Upper Riphean) deposits in the Ural Mountains. In between lies the Vychegda Formation, a 600 m siliciclastic succession that has no counterpart in classic EEP stratigraphy.

Vychegda microfossils can be separated into three assemblages. The upper part of the formation contains large, profusely ornamented acritarchs broadly comparable to those of the Ediacaran Complex Acanthomorph Palynoflora, including species of the genera Alicesphaeridium, Asterocapsoides, Cavaspina and Tanarium confined to Ediacaran-aged assemblages elsewhere. Diverse large acanthomorphs are known from Ediacaran strata around the world, but have not previously been recognized from the EEP, an absence attributed to a hiatus between the glacial Laplandian (>635 Ma) and Redkino (mostly <555 Ma) successions. The large acanthomorphic acritarchs record eukaryotic organisms with resting stages in their life cycles and likely include egg or diapause cysts of early animals. In contrast, the lower Vychegda assemblage, found in the basal 10 m of the succession, contains taxa typical of earlier Neoproterozoic successions. The middle assemblage contains only simple filaments and spheroidal acritarchs.

The most parsimonious interpretation of Vychegda biostratigraphy is that pre-Marinoan rocks in the basal part of the formation are separated by a cryptic unconformity from early and middle Ediacaran deposits above. This interpretation is consistent with data from China and Australia, which indicate that the major paleontological transition to diverse ECAP assemblages took place within the Ediacaran Period and not in association with the preceding ice age. Vychegda acritarch assemblages thus contribute to a biostratigraphic model for the initial Ediacaran boundary.

Trilobites of this suborder from Europe and North America have not been studied in detail, in contrast to the attention given to relationships within the orders Agnostida and Ptychopariina. The basis of the Corynexochina is the type species of Corynexochus from the middle Cambrian of Sweden. The type material redescribed here is only the cranidium, and is inadequate for diagnosis of the genus. A species attributed to this genus occurring in the Cambrian of southern France is represented by entire dorsal exoskeletons and is urgently in need of redescription. Similar material is recorded in northern Spain. Both complete exoskeletons and growth stages of Corynexochina have been described from Cambrian strata in Russia, Australia, Morocco and China, showing the wide geographical range and varied morphology of the Suborder. The type species of two genera from boulders of middle Cambrian age found in Quebec, Canada, are redescribed from exceptionally well preserved, though small, specimens. They appear to represent a distinct group related to some of the Zacanthoididae. Families of Corynexochina are inadequately discriminated one from another, so that a family name can only be used with question. Until this is remedied, diagnosis of a new group is not possible.

From the oldest Cretaceous marine sediments of Jamaica, the Copper Limestone within the Devils Racecourse Formation (Benbow Inlier, Clarendon Block), the oldest known coral fauna of the Caribbean is described. the small but diverse fauna encompasses 18 species in 17 genera of the suborders Amphiastraeina, Archeocaeniina, Heterocoeniina, Faviina, Fungiina, Microsolenina, and Stylinina. the fauna contains the first representatives of the suborder Amphiastraeina in the Caribbean and the Americas. One genus of the family Amphiastreidae, Monoaulastrea, and three species—Monoaulastrea rawi, Latusastrea rubrolineata, Camptodocis corralesi—are described as new. the preoccupied coral genus Floria is replaced by the new name Floriastrea. the new fauna shows relationships to faunas from the late Berriasian to late Albian. Most species are shared with the Hauterivian faunas from Georgia in the central Tethys and the Paris Basin in the Boreal, but also with younger faunas such as the Barremian of Central Mexico, the early Aptian of Greece and the early Albian of the Bisbee Basin (Northern Mexico).

Ediacaran fronds at Spaniard's Bay on the Avalon Peninsula of Newfoundland exhibit exquisite, three-dimensional preservation with morphological features less than 0.05 mm in width visible on the best preserved specimens. Most of the nearly 100 specimens are juvenile rangeomorphs, an extinct Ediacaran clade that numerically dominated the early evolution of complex multicellular life. Spaniard's Bay rangeomorphs are characterized by cm-scale architectural elements exhibiting self-similar branching over several fractal scales that were used as modules in construction of larger structures. Four taxa of rangeomorph fronds are present – Avalofractus abaculus n. gen. et sp., Beothukis mistakensis Brasier and Antcliffe, Trepassia wardae (Narbonne and Gehling), and Charnia cf. C. masoni Ford. All of these taxa exhibit an alternate array of primary rangeomorph branches that pass off a central stalk or furrow that marks the midline of the petalodium. Avalofractus is remarkably self similar over at least four fractal scales, with each scale represented by double-sided rangeomorph elements that were constrained only at their attachment point with the higher-order branch and thus were free to rotate and pivot relative to other branches. Beothukis is similar in organization, but its primary branches show only one side of a typical rangeomorph element, probably due to longitudinal branch folding, and the position of the individual branches was moderately constrained. Trepassia shows only single-sided branches with both primary and secondary branches emanating from a central stalk or furrow; primary branches were capable of minor pivoting as reflected in bundles of secondary branches. Charnia shows only single-sided primary branches that branch from a zigzag central furrow and that were firmly constrained relative to each. This sequence provides a developmental linkage between Rangea-type and Charnia-type rangeomorphs. Avalonian assemblages show a wide array of rangeomorph constructions, but later Ediacaran assemblages contain a lower diversity of rangeomorphs represented mainly by well-constrained forms.

Over the course of the last two decades, the baenid taxon Plesiobaena has typically been thought to consist of two named species, Plesiobaena antiqua (Campanian) and Plesiobaena putorius (Paleocene), along with an unnamed species from the Maastrichtian, but the interrelationship of these three taxa was never explored in an explicit phylogenetic context. Herein we present or re-describe a number of relevant specimens and provide a cladistic analysis of Baenidae using species only as terminal taxa. The phylogenetic analysis clearly reveals that Plesiobaena in the traditional sense is a paraphyletic assemblage relative to the clade formed by Gamerabaena sonsalla and Palatobaena spp., thus demanding some nomenclatural adjustments. In particular, Plesiobaena putorius is moved to a new genus, Cedrobaena, and the unnamed taxon from the Maastrichtian is formally named Peckemys brinkman. Many of the new Cedrobaena putorius and Peckemys brinkman specimens described herein were found at the Turtle Graveyard locality in Slope County, North Dakota, along with four other turtle taxa, increasing the turtle diversity of this locality to at least six taxa. Although this indicates that Turtle Graveyard is the world's most diverse fossil turtle thanatocoenosis, a comparable diversity is found in modern river systems in the southeastern United States today. Our phylogenetic analysis indicates that seven out of nine latest Cretaceous baenid turtle lineages survived into the Paleocene, four of which are interpreted as being durophagous.

Although used in biostratigraphy and in studies of early Cambrian trilobite evolution, the olenelloid genus Peachella has received little research attention. The ontogenetic and evolutionary origins of its derived features—an effaced cephalon and grossly inflated genal spines—have remained mysterious. Based on examination of new and existing collections, P. iddingsi and P. brevispina are here described in detail, including aspects of their respective ontogenies and the first description of the thorax of P. iddingsi. A new monotypic genus, Eopeachella, is also described from recently collected material from the Delamar Member of the Pioche Formation, Nevada. Eopeachella angustispina n. gen. n. sp., is less derived and stratigraphically older than both Peachella species and bridges the morphological gap between Peachella and typical olenelloids. The study reveals that cephalic effacement was progressively attained during both ontogeny and phylogeny in the Eopeachella + Peachella clade. Comparative ontogeny with other olenelloids reveals that progressive effacement was a trend superimposed upon and independent of a conserved pattern of ontogenetic shape change in the glabella and did not represent a peramorphic “extension” of glabellar ontogeny. Genal spine inflation was also achieved progressively (in a proximal-to-distal direction) through both ontogeny and phylogeny in the Eopeachella + Peachella clade. Genal spine inflation that convergently arose in later trilobite groups may have been similarly ontogenetically dynamic. Discovery of E. angustispina and P. brevispina in the Delamar Member raises olenelloid diversity in this member to at least 20 species; a higher diversity than in any coeval unit.

In the Conglomerate Mesa area in the southeastern Inyo Mountains, east-central California, a series of distinctive fusulinid assemblages ranging in age from late Artinskian to Kungurian or Roadian was developed in units 7–10 of the sedimentary rocks of Santa Rosa Flat (part of the Owens Valley Group). The fauna of unit 7 shows some eastern Klamath Mountains affinity, but most of the species in unit 7 and the lower half of unit 8 are highly endemic and comprise three new genera with 12 new species, two unusual unassigned forms, and two other new species assigned to previously described genera. New taxa include: Crenulosepta new genus with five new species, C. inyoensis, C. delicata, C. fusiformis, C. rossi, and C. wahlmani; Nigribaccinus new genus with three new species, N. giganteus, N. elegans, and N.? nestelli; and the new genus Inyoschwagerina with four new species, I. magnifica, I. elayeri, I. elongata, and I.? linderae. Cuniculinella Skinner and Wilde, 1965, is represented by one new species, C. parva, and Skinnerella Coogan, 1960 by one new species, S.? mcallisteri. Faunas from the upper half of unit 8, unit 9, and unit 10 have a strong West Texas affinity. New species from these units are Skinnerella davydovi, S. hexagona, Parafusulina cerrogordoensis, P. complexa, P. halli, P. owensensis, and P. ubehebensis.

The dramatic late Early Ordovician radiation of cephalopods on tropical paleocontinents is illustrated by the diverse fauna (21 genera, 30 species) of the Fort Cassin Formation (Floian and lower Blackhillsian Stage) in northeast Laurentia. Cephalopods occur through the thin (ca. 30–65 m) depositional sequence of the Fort Cassin but are most common and diverse in mollusk-rich, trilobite-poor parts of the formation that characterize the thrombolite-bearing intervals in the shoaling part of the highstand systems tract. This lithofacies-biofacies linkage persists from the Tribes Hill and Rochdale Formations (lower and lower upper Tremadocian, and upper Skullrockian and Stairsian Stages, respectively), and suggests that the Early Ordovician radiations of cephalopods took place in shallow-marine, thrombolite reef facies of tropical carbonate platforms. These habitats differed strongly from the near-shore, peritidal habitats of the older Cambrian evolutionary radiation. Genus-level diversity and absolute abundance changed little through the Skullrockian-Blackhillsian, but morphologic diversity and body size increased dramatically by the late Early Ordovician. The morphological diversification suggests cephalopods diversified into a wider variety of macropredators and more complex late Early Ordovician ecosystems. Anrangeroceras whitehallense n. gen. and n. sp. is proposed. The following are emended: the Protocycloceratidae, Centrotarphyceras and C. seelyi, Protocycloceras and P. lamarcki, and Rudolfoceras cornuoryx. The following are indeterminate and abandoned: Baltoceras? pusillum Ruedemann, 1906; Comeroceras annuliferum Flower, 1941; Cyptendoceras whitfieldi Ulrich et al., 1944; Endoceras? champlainense Ruedemann, 1906; Wolungoceras valcourense Flower, 1964. Beekmanoceras Ulrich and Foerste, 1936 is a gastropod.

Apektocrinus ubaghsi new genus and species is a monospecific taxon assigned to the new family Apektocrinidae based on additional preparation of a single previously studied specimen. Apektocrinus is among the oldest known crinoids (Early Tremadoc, Early Ordovician). Although expressing crinoid apomorphies, it is interpreted as retaining plesiomorphies in its arms reflecting early edrioasteroid rather than blastozoan (eocrinoid) ancestry. Apomorphies represent basal crinoid and cladid (crownward) levels of phylogeny.

Restudy fortifies previous reports of the presence of a basal echinoderm plesiomorphy; floor plates above brachials in the arms of Apektocrinus, as well as in other approximately contemporary crinoids. Apektocrinus furnishes the first record of podial basins in crinoid arms. Arms and calyx of Apektocrinus merge gradually, facilitated by continuations of interbrachials (extraxial body plates) extending onto the arms and separating floor plates from brachials. These arm interbrachials, which diminish and pinch out distally as floor plates nestle into the brachial (adoral) groove, have not been recognized as such in crinoids.

Assessment of ontogenetic and geographic variation can have substantial influence on species delimitation and thereby on perceived patterns of species-level morphological variation and diversity in space and time. Here we describe the ontogeny and intraspecific variation of the early Cambrian trilobite, Zacanthopsis palmeri n. sp., based on silicified material from east-central Nevada, USA. Zacanthopsis palmeri is the oldest documented Cambrian corynexochine to shift from possessing a fused rostal-hypostomal plate to a functional hypostomal suture in mature specimens during ontogeny. Six geographically distinct samples of mature Z. palmeri from a single silicified limestone bed traceable over tens of kilometers in east-central Nevada permit exploration of geographic variation within this species using geometric morphometric methods. No one sample encompasses all of the shape variation expressed by Z. palmeri and several geographically segregated samples show some degree of morphological separation in pairwise comparison. Nonetheless, these samples are not qualitatively or quantitatively different from one another when all samples are taken into account. The degree of variation within Z. palmeri is similar in magnitude to the differences between other species in the genus known from much less material.

A rich and diverse micromammal fauna from the late Turolian (MN13) locality of Negratín-1 (Guadix Basin, southern Spain) is described. The faunal list of this site includes Apodemus gudrunae, Occitanomys alcalai, Stephanomys dubari, Paraethomys meini, Myocricetodon jaegeri, Debruijnimys almenarensis, Apocricetus alberti, Ruscinomys sp., Eliomys sp., Atlantoxerus sp., Parasorex ibericus, and Soricidae indet. This is the most nearly complete mammal fauna from the Miocene of the Guadix Basin and allows precise correlations with localities from other Iberian areas. In addition, some of the taxa identified in Negratín-1 are useful as palaeoecological indicators (Myocricetodon, Debruijnimys, Atlantoxerus), evidencing warm and dry climatic conditions. But the principal interest of the fauna from Negratín-1 is the presence of several species of African origin, the gerbillids Debruijnimys almenarensis and Myocricetodon jaegeri, which are recognized for the first time in Europe. We also ascribe to M. jaegeri the population from the upper Turolian karst infilling of Almenara-M. This finding constitutes new evidence for faunal exchanges between North Africa and the Iberian Peninsula during the Messinian Salinity Crisis.

Morphometric analyses of shell morphology in the Cretaceous nautiloid Eutrephoceras clementinum (d'Orbigny, 1840) (Cephalopoda, Mollusca) from the Ariyalur area, southern India, reveal ontogenetic change from hatching to maturity as well as intra-specific variation in shell morphology. the shell breadth has a negative allometric relationship with shell diameter and with whorl height, and the umbilicus diameter has a positive allometric relationship with shell diameter. This shows that shell shape became relatively thinner with less variation, and the umbilicus diameter became relatively broader with growth. the siphuncle position moves from a dorso-central to ventro-central position with growth. A constriction was recognized on the early whorl at 20 mm in shell diameter, and the interval angles of succeeding septa were changed at the 8th septum, indicating that they hatched at this stage. the bending of umbilical walls of apertures toward the center of coiling suggests that E. clementinum attained maturity at about 115 mm in shell diameter. the comparison of the shell morphology of E. clementinum with that of E. bouchardianum (d'Orbigny, 1840) reported in the literature clarifies their difference in whorl shape and umbilical size, especially in the adult stage. This kind of morphometric study of nautiloids is essential for elucidating their adaptive designs for environment and mode of life, functional shell morphology, taxonomy, phylogeny, and evolution.

Platycrinites is traditionally one of the more recognizable crinoids, a camerate crinoid with very few if any fixed brachials or interradials and a helically twisted column. Accordingly, many taxa have been assigned to this genus. With a better understanding of the Platycrinitidae, these characters actually unite the family Platycrinitidae rather than the genus. Further, use of different genus-diagnostic characters in Western Europe versus North America has resulted in a confused systematics for this important late Paleozoic family. Here, we objectively define genera within the Platycrinitidae and assign all species to either newly defined or newly named genera. A phylogenetic hypothesis, incorporating both parsimony-based character analysis and stratigraphic ranges, of the genera within the Platycrinitidae is presented.

With consideration of the type species, Platycrinites laevis Miller, 1821, Platycrinites sensu stricto is distinguished from Platycrinites sensu lato, which is used for species that cannot be assigned with confidence to any objectively defined genus. New genera are Artaocrinus n. gen., Collicrinus n. gen., Elegantocrinus n. gen., and Laticrinus n. gen.; and Exsulacrinus Bowsher and Strimple, 1986 is designated a junior synonym of Platycrinites s.s. Collicrinus shumardi n. gen. and sp., Laticrinus oweni n. gen. and sp., and Laticrinus wachsmuthi n. gen. and sp. are described; and Platycrinites formosus approximatus (Miller and Gurley, 1896a) is designated a junior synonym of Platycrinites formosus (Miller and Gurley, 1895a), which is reassigned here to Collicrinus n. gen. Platycrinites s.s. now includes 14 species and species-level taxa, and 76 species are assigned to Platycrinites s.l. Ten species are designated nomina dubia, as are taxa based solely on columnals or pluricolumnals. Two species are designated nomina nuda, and two are transferred to genera outside of the Platycrinitidae. In addition, twenty-seven species and four open-nomenclature taxa are each reassigned to a different genus.

New fusulinid collections from the Baoshan Block in southwest China necessitate paleobiogeographic reevaluation of the Mid-Permian fusulinids in this region. From Xiaoxinzhai Section in the southern Baoshan Block, 32 fusulinid species of nine genera are described and illustrated. Among them, Eopolydiexodina parva is a new species, and elements of Neoschwagerinidae and Verbeekinidae are confirmed. The studied fusulinids are ascendingly grouped into three biozones: the Schwagerina yunnanensis Range Zone, Eopolydiexodina Abundance Zone, and Sumatrina annae Range Zone. The lower two could be assigned in age to the Murgabian and the uppermost one to the Midian. Midian fusulinids are for the first time reported from the Baoshan Block. In terms of fusulinid paleobiogeography, these three assemblages should belong to the western Tethyan Province A because of the presence of Eopolydiexodina and characteristic Tethyan genera, e.g., Verbeekina, Sumatrina, and Pseudodoliolina. Moreover, these assemblages may occupy a comparatively high latitudinal region within Tethyan Realm, judging from the overall low diversity.

During the Eocene, Hahajima Island of the Ogasawara (Bonin) Islands of the Izu-Mariana Arc in the North Pacific was located near the present-day position of western Pacific Micronesia. We identified 17 Eocene ostracode species from the island, of which are new species and likely endemic to this island or to the West Pacific. These new species are systematically described herein and include: Costa matsumarui n. sp., Cytherelloidea ogasawaraensis n. sp., Havanardia ujiiei n. sp., Jugosocythereis nishii n. sp., Neonesidea boninensis n. sp., Schizocythere antiquimicronesiana n. sp., and Uroleberis hahajimaensis n. sp. The Eocene ostracode fauna has a higher rate of endemism than does the modern Micronesian fauna and contains Tethyan genera. These findings contradict a hypothesis that the Pacific fauna had a higher endemism rate after the Paleogene. The findings support another hypothesis that some genera invaded the Pacific from Tethys during the Paleogene. They suggest that West Pacific species did not disperse to the periphery of the Indo-West Pacific region during the Middle–Late Eocene. The “center of origin” hypothesis cannot be applied to Middle–Late Eocene marine ostracode biogeography.

Upper Ordovician radiolarians are described from limestone within the Malongulli Formation in the Cliefden Caves area using revised systematics. Eight genera and 12 species are described, including the following four new species: Protoceratoikiscum crossingi, Haplotaeniatum ovatum, Haplotaeniatum prolatum, and Borisella dunhilli, and two new combinations, Borisella subulata and Haplotaeniatum spongium. All samples are dominated by Kalimnasphaera maculosa, B. subulata, and Palaeoephippium octaramosum with lesser abundances of Haplotaeniaum spp. and Inanigutta complanata, and rare occurrences of Protoceratoikicsum spp. The rare species Etymalbaillella yennienii is reported for the first time outside of China. The Malongulli Formation is upper Eastonian through lower Bolindian (Katian global stage) based on graptolite and conodont biostratigraphy. From a stratigraphic standpoint, the limestone intervals sampled appear to represent two or possibly three stratigraphically separate intervals within the Malongulli Formation. Conodonts recovered from Coppermine Creek, Angullong/Belubula, and Gleesons Creek localities occur in the lower and middle parts of the formation and fall within one conodont zone, the O. velicuspis Zone. The stratigraphic position of the limestone at the Sugarloaf Creek locality is higher, possibly as high as lower Bolindian, based on proximity to the top of the formation where Bolindian graptolites have been recovered. Despite the different stratigraphic positions of the limestones, the radiolarians contained within are essentially the same fauna, barring some differences in relative abundance in Haplotaeniatum and Palaeoephippium. The Malongulli fauna is discussed with respect to other Upper Ordovician faunas, most notably those from siliceous facies in the eastern Lachlan Orogen and from the Hanson Creek Formation of Nevada, U.S. The radiolarian species occur across different depositional environments and from a range of geographically widespread localities, which bodes well for them being recognized as biostratigraphically important faunal markers with correlation potential within the Katian.

The basal Cambrian marks the beginning of an important chapter in the history of life. However, most paleontological work on the basal Cambrian has been focused on skeletal animal fossils, and our knowledge about the primary producers—cyanobacteria and eukaryotic phytoplankton (e.g., acritarchs)—is limited. In this research, we have investigated basal Cambrian acritarchs, coccoidal microfossils, and cyanobacteria preserved in phosphorites and cherts of the Yanjiahe Formation in the Yangtze Gorges area (South China) and the Yurtus Formation in the Aksu area (Tarim Block, northwestern China). Our study confirms the occurrence in these two formations of small acanthomorphic acritarchs characteristic of the basal Cambrian Asteridium–Comasphaeridium–Heliosphaeridium (ACH) assemblage. These acritarchs include abundant Heliosphaeridium ampliatimi (Wang, 1985) Yao et al., 2005, common Yurtusia uniformis n. gen. and n. sp., and rare Comasphaeridium annulare (Wang, 1985) Yao et al., 2005. In addition, these basal Cambrian successions also contain the clustered coccoidal microfossil Archaeophycus yunnanensis (Song in Luo et al., 1982) n. comb., several filamentous cyanobacteria [Cyanonema majus n. sp., Oscillatoriopsis longa Timofeev and Hermann, 1979, and Siphonophycus robustum (Schopf, 1968) Knoll et al., 1991], and the tabulate tubular microfossil Megathrix longus L. Yin, 1987a, n. emend. Some of these taxa (e.g., H. ampliatum, C. annulare, and M. longus) have a wide geographic distribution but occur exclusively in basal Cambrian successions, supporting their biostratigraphic importance. Comparison between the stratigraphic occurrences of microfossils reported here and skeletal animal fossils published by others suggests that animals and phytoplankton radiated in tandem during the Cambrian explosion.