increasing latitudinal thermal gradients at the onset of major ice sheet expansion on antarctica and progressive cooling through the neogene and quaternary towards a bipolar glaciated world. this caused diatoms to take in less silica for the formation of their frustules. increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic upwelling. dinoflagellata dinoflagellates are mainly represented as fossils by fossil dinocysts, which have a long geological record with lowest occurrences during the mid-triassic, whilst geochemical markers suggest a presence to the early cambrian. some evidence indicates dinosteroids in many paleozoic and precambrian rocks might be the product of ancestral dinoflagellates (protodinoflagellates). molecular phylogenetics show that dinoflagellates are grouped with ciliates and apicomplexans (=sporozoa) in a well-supported clade, the alveolates. the closest relatives to dinokaryotic dinoflagellates appear to be apicomplexans, perkinsus, parvilucifera, syndinians, and oxyrrhis. molecular phylogenies are similar to phylogenies based on morphology. the earliest stages of dinoflagellate evolution appear to be dominated by parasitic lineages, such as perkinsids and syndinians (e.g. amoebophrya and hematodinium). all dinoflagellates contain red algal plastids or remnant (nonphotosynthetic) organelles of red algal origin. the parasitic dinoflagellate hematodinium however lacks a plastid entirely. some groups that have lost the photosynthetic properties of their original red algae plastids has obtained new photosynthetic plastids (chloroplasts) through so-called serial endosymbiosis, both secondary and tertiary. like their original plastids, the new chloroplasts in these groups can be traced back to red algae, except from those in the members of the genus lepidodinium, which possess plastids derived from green algae, possibly trebouxiophyceae or ulvophyceae. lineages with tertiary endosymbiosis are dinophysis, with plastids from a cryptomonad, the karenia, karlodinium, and takayama, which possess plastids of haptophyte origin, and the peridiniaceae, durinskia and kryptoperidinium, which has plastids derived from diatoms some species also perform kleptoplasty. dinoflagellate evolution has been summarized into five principal organizational types: prorocentroid, dinophysoid, gonyaulacoid, peridinioid, and gymnodinoid. the transitions of marine species into fresh water have been infrequent events during the diversification of dinoflagellates and in most cases have not occurred recently, possibly as late as the cretaceous. recently, the "living fossil" dapsilidinium pastielsii was found inhabiting the indo-pacific warm pool, which served as a refugium for thermophilic dinoflagellates. foraminifera molecular clocks indicate that the crown-group of foraminifera likely evolved during the neoproterozoic, between 900 and 650 million years ago; this timing is consistent with neoproterozoic fossils of the closely related filose amoebae. as fossils of foraminifera have not been found prior to the very end of the ediacaran, it is likely that most of these proterozoic forms did not have hard-shelled tests. the mysterious paleodictyon has been interpreted as a fossil xenophyophore but this remains controversial. cutaway view of a fusulinid a fossil test from a planktonic globigerininan foraminifera due to their non-mineralised tests, "allogromiids" have no fossil record. the mysterious vendozoans of the ediacaran period have been suggested to represent fossil xenophyophores. however, the discovery of diagenetically-altered c27 sterols associated with the remains of dickinsonia cast doubt on this identification and suggest it may instead be an animal. other researchers have suggested that the elusive trace fossil paleodictyon and its relatives may represent a fossil xenophyophore and noted the similarity of the extant xenophyophore occultammina to the fossil; however, modern examples of paleodictyon have not been able to clear up the issue and the trace may alternately represent a burrow or a glass sponge. supporting this notion is the similar habitat of living xenophyophores to the inferred habitat of fossil graphoglyptids; however, the large size and regularity of many graphoglyptids as well as the apparent absence of xenophyae in their fossils casts doubt on the possibility. as of 2017 no definite xenophyophore fossils have been found. test-bearing foraminifera have an excellent fossil record throughout the phanerozoic eon. the earliest known definite foraminifera appear in the fossil record towards the very end of the ediacaran; these forms all have agglutinated tests and are unilocular. these include forms like platysolenites and spirosolenites. single-chambered foraminifera continued to diversity throughout the cambrian. some commonly encountered forms include ammodiscus, glomospira, psammosphera, and turritellella; these species are all agglutinated. they make up part of the ammodiscina, a lineage of spirillinids that still contains modern forms. later spirillinids would evolve multilocularity and calcitic tests, with the first such forms appearing during the triassic; the group saw little effects on diversity due to the k-pg extinction. the earliest multi-chambered foraminifera are agglutinated species, and appear in the fossil record during the middle cambrian period. due to their poor preservation they cannot be positively assigned to any major foram group. the earliest known calcareous-walled foraminifera are the fusulinids, which appear in the fossil record during the llandoverian epoch of the early silurian. the earliest of these were microscopic, planispirally coiled, and evolute; later forms evolved a diversity of shapes including lenticular, globular, and elongated rice-shaped forms. later species of fusulinids grew to much larger size, with some forms reaching 5 cm in length; reportedly, some specimens reach up to 14 cm in length, making them among the largest foraminifera extant or extinct. fusulinids are the earliest lineage of foraminifera thought to have evolved symbiosis with photosynthetic organisms. fossils of fusulinids have been found on all continents except antarctica; they reached their greatest diversity during the visean epoch of the carboniferous. the group then gradually declined in diversity until finally going extinct during the permo-triassic extinction event. during the tournaisian epoch of the carboniferous, miliolid foraminifera first appeared in the fossil record, having diverged from the spirillinids within the tubothalamea. miliolids suffered about 50% casualties during both the permo-triassic and k-pg extinctions but survived to the present day. some fossil miliolids reached up to 2 cm in diameter. the earliest known lagenid fossils appear during the moscovian epoch of the carboniferous. seeing little effect due to the permo-triassic or k-pg extinctions, the group diversified through time. secondarily unilocular taxa evolved during the jurassic and cretaceous. the earliest involutinid fossils appear during the permian; the lineage diversified throughout the mesozoic of eurasia before apparently vanishing from the fossil record following the cenomanian-turonian ocean anoxic event. the extant group planispirillinidae has been referred to the involutinida, but this remains the subject of debate. the robertinida first appear in the fossil record during the anisian epoch of the triassic. the group remained at low diversity throughout its fossil history; all living representatives belong to the robertinidae, which first appeared during the paleocene. the first definite rotaliid fossils do not appear in the fossil record until the pliensbachian epoch of the jurassic, following the triassic-jurassic event. diversity of the group remained low until the aftermath of the cenomanian-turonian event, after which the group saw a rapid diversification. of this group, the planktonic globigerinina—the first known group of planktonic forams—first appears in the aftermath of the toarcian turnover; the group saw heavy losses during both the k-pg extinction and the eocene-oligocene extinction, but remains extant and diverse to this day. an additional evolution of planktonic lifestyle occurred in the miocene or pliocene, when the rotaliid neogallitellia independently evolved a planktonic lifestyle. radiolaria fossil radiolarianx-ray microtomography of triplococcus acanthicus this is a microfossil from the middle ordovician with four nested spheres. the innermost sphere is highlighted red. each segment is shown at the same scale. the earliest known radiolaria date to the very start of the cambrian period, appearing in the same beds as the first small shelly fauna—they may even be terminal precambrian in age. they have significant differences from later radiolaria, with a different silica lattice structure and few, if any, spikes on the test. ninety percent of radiolarian species are extinct. the skeletons, or tests, of ancient radiolarians are used in geological dating, including for oil exploration and determination of ancient climates. some common radiolarian fossils include actinomma, heliosphaera and hexadoridium excavata evolutionary history of coccolithophores (a) coccolithophore species richness over time (b) the fossil record of major coccolithophore biomineralization innovations and morphogroups hacrobia coccolithophores: the diagram on the right shows —> (a) coccolithophore species richness over time combining heterococcoliths and nannoliths. q, quaternary; n, neogene; pal, paleogene; e/o, eocene/oligocene glacial onset event; petm, paleocene/eocene thermal maximum warming event; k/pg, cretaceous/paleogene; oae, oceanic anoxic event; t-oae, toarcian oceanic anoxic event; t/j, triassic/jurassic; p/t, permian/triassic; mass ext., mass extinction. (b) the fossil record of major coccolithophore biomineralization innovations and morphogroups, including the first appearances of muroliths (simple coccoliths with narrow, wall-like rims), placoliths (coccoliths with broad shields that interlock to form strong coccospheres), holococcoliths (coccoliths formed from microcrystals in the haploid life cycle phase), braarudosphaera (pentagonal, laminated nannoliths forming dodecahedral coccospheres); calciosolenia (distinct, rhombic murolith coccoliths), coccolithus (long-ranging and abundant cenozoic genus), isochrysidales (dominant order that includes emiliania, gephyrocapsa, and reticulofenestra). significant mass extinctions and paleoceanographic/paleoclimatic events are marked as horizontal lines. opisthokonta (in part) (reclassified) golden algae because many of these organisms had a silica capsule, they have a relatively complete fossil record, allowing modern biologists to confirm that they are, in fact, not derived from cyanobacteria, but rather an ancestor that did not possess the capability to photosynthesize. many of the chrysophyta precursor fossils entirely lacked any type of photosynthesis-capable pigment. most biologists believe that the chrysophytes obtained their ability to photosynthesize from an endosymbiotic relationship with fucoxanthin-containing cyanobacteria. green algae the ancestral green alga was a unicellular flagellate.