Unikonta

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The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.

Green peach aphid ( Myzus persicae ) infected with the fungus Pandora neoaphidis ; Both types belong to the Unikonta

The term Unikonta covers a certain group of living organisms with a cell nucleus ( eukaryota ). All Unikonta contain (or probably originally appeared) unikonta cells . Unikonte cells are cells that move with the help of a single flagellum . Nowadays, certain single cells from the Amoebozoa group could still closely resemble this original appearance. A modified variant would also be the human sperm, for example .

The Amoebozoa belong to the Unikonta group . The majority of the members of this group are not flagellated like an amoeba , but also include simply flagellated forms. On the other hand, the group of Unikonta includes the Schubgeissler ( Opisthokonta ). The Opisthokonta are further subdivided, especially into the large groups of animals ( Animalia ) and chitin mushrooms (real mushrooms, Fungi ).

All other eukaryota are not Unikonta. Instead, they should form the large group of Bikonta . Among other things, the Bikonta are said to include such well-known life forms as red algae , land plants , brown algae , diatoms and ciliate animals . Biconts Living things possess (or probably originally did) bicontos. Cells, i.e. cells with two flagella. This basically distinguishes them cytologically from the Unikonta.

However, it is not entirely undisputed whether the Bikonta actually all descend from a last common ancestor, i.e. whether they form a monophylum . Because of this uncertainty, the Bikonta are currently not included in the comprehensive systematics of eukaryotes of the German-language Wikipedia. In contrast, the Unikonta taxon was relatively well documented. However, due to investigations in 2012 the Unikonta taxon was replaced by the taxon Amorphea .

Features to differentiate Unikonta - Bikonta

The Unikonta set themselves apart from all other living beings with cells with a nucleus due to certain molecular biological and cell biological characteristics . These remaining eukaryota are then summarized as Bikonta and compared to the Unikonta as a sister group .

Feature of fusion genes

In order to distinguish between Unikonta and Bikonta on the molecular biological level, the condition of five specific genes is examined. All five genes are needed to build nucleotides . So they are important for the synthesis of the molecules DNA and RNA :

  1. Gene for the enzyme carbamoyl phosphate synthase II : The carbamoyl phosphate synthase II catalyses the synthesis of the substance carbamoyl phosphate from hydrogen carbonate , glutamine and adenosine triphosphate in eukaryota . This synthesis is the first step in a six-step synthetic route for the production of uridine monophosphate . All other pyrimidine nucleotides that occur in DNA and RNA are then produced from uridine monophosphate ( pyrimidine de novo synthesis ).
  2. Gene for the enzyme aspartate transcarbamoylase : The aspartate transcarbamoylase catalyzes the synthesis of the substance carbamoyl aspartate from carbamoyl phosphate and aspartate . This synthesis is the second step in the six-step synthetic route for the production of uridine monophosphate.
  3. Gene for the enzyme dihydroorotase : Dihydroorotase catalyzes the condensation reaction of carbamoyl aspartate to form the ring-shaped dihydroorotate . This synthesis is the third step in the six-step synthetic route for the production of uridine monophosphate.
  4. Gene for the enzyme thymidylate synthase : The thymidylate synthase catalyzes the synthesis of 2'-deoxythymidine-5'-monophosphate from 2'-deoxyuridine-5'-monophosphate . During this reaction, methylene tetrahydrofolate is converted to 7,8-dihydrofolate. Afterwards, 2'-deoxythymidine-5'-monophosphate is used for DNA molecules, while the 7,8-dihydrofolate is further processed to tetrahydrofolate with the catalysis of dihydrofolate reductase .
  5. Gene for the enzyme dihydrofolate reductase : The dihydrofolate reductase catalyzes the reduction of folate and 7,8- dihydrofolate to tetrahydrofolate . Tetrahydrofolate is required, among other things, for the biosynthesis of the nucleotides thymidine monophosphate and inosine monophosphate ( purine de novo synthesis ).

In molecular biology, the Unikonta can be recognized by the fact that the three genes for the enzymes carbamoyl phosphate synthase II, aspartate transcarbamoylase and dihydroorotase are fused into one gene. After the first three letters of the enzyme, this becomes triple-gene fusion. Called CAD . CAD is transcribed as a contiguous mRNA . After translation , the gene product is a coherent, trifunctional protein ( multienzyme protein ): a giant macropeptide that simultaneously performs the three catalytic functions of carbamoyl phosphate synthase II, aspartate transcarbamoylase and dihydroorotase. In this way, the first three steps of the six-step synthesis route for the production of uridine monophosphate are catalyzed together in the same molecule, saving time. In contrast to the Unikonta, the Bikonta have no CAD. In the Bikonta, the three genes are present individually.

The Bikonta in turn have a simple gene fusion of the genes thymidylate synthase and dihydrofolate reductase. The gene product is a coherent, bifunctional protein: a macropeptide that simultaneously performs the two catalytic functions of dihydrofolate reductase and thymidylate synthase. During the catalysis of the thymidylate synthesis, dihydrofolate is produced. The subsequent reduction of the substance to tetrahydrofolate is catalyzed in the same macropeptide to save time. In contrast to the Bikonta, this gene fusion cannot be found in the Unikonta. In the Unikonta, the two genes are present individually.

Characteristic of phosphofructokinase

The Unikonta also have a particularly large form of the enzyme phosphofructokinase . The enzyme in Unikonta is roughly twice as large as the phosphofructokinase in Prokaryota . The enlargement is accompanied by improved controllability. Both types of phosphofructokinase can be activated by ADP and AMP , but the uniconted phosphofructokinase can also be activated by fructose-1,6-bisphosphate . In addition, the latter can be inhibited by ATP and citrate . The gene for the enzyme phosphofructokinase probably entered the eukaryotic cell with the endosymbiosis of the mitochondrion . In the last common ancestor of all Unikonta occurring today, the gene was duplicated so that two gene copies were present. The two gene copies then fused to form one gene. The gene product of this gene thus had two active centers for the same catalysis. Then the active center closer to the carboxy terminus evolved into a new allosteric center . The unique variant of phosphofructokinase owes its extensive controllability to this new allosteric center. The large and extensively regulated phosphofructokinase is a common feature of all Unikonta. It is not found in Bikonta, nor is the mitochondrial precursor gene. It was probably lost with the Bikonta. Variants of the enzyme phosphofructokinase, which are found today in Bikonta, do not resemble the unikonten form and represent own developments, which probably go back to various horizontal gene transfers .

Characteristic α-amylase

Many eukaryotic and prokaryotic life forms have genes for the production of the enzyme α-amylase . α-Amylases catalyze the hydrolysis of the polysaccharides amylose and amylopectin to form maltotriose , maltose and glucose . It has been found that most Unikonta use the same variant of α-amylase. This variant was the first time in a slime mold in which Amoebozoa - genus Dictyostelium found. It is therefore called a dictyo-type α-amylase . Genes for α-amylases of the dictyo type are found in the Unikonta groups of the Amoebozoa and the Nucletmycea ( chitin fungi and the like). Dictyo-type α-amylases are also found in animals . But here only with groups that are not to the two-sided animals ( Bilateria belong), ie at Choanoflagellata , sponges and coelenterates .

It is believed that the Dictyo-type α-amylase is a common derived characteristic of all Unikonta. As an exception, the α-amylase from Dictyo type when missing Amoebozoa - genus Entamoeba . Here the gene could have been lost in the course of their parasitic lifestyle. The α-amylase of the dictyo type is also absent in all bilateral animals (Bilateria) . Instead, they have their own form of α-amylases. It is called animal amylase , although it is exactly a bilateria amylase , while the other animals (choanoflagellata, sponges and coelenterates) still have α-amylases of the dictyo type. It can be assumed that the animal amylase of the bilateral animals comes from bacteria of the order Alteromonadales ( Proteobacteria ) and that it reached the last common ancestor of all bilateral animals living today through a horizontal gene transfer .

In addition, α-amylases of the dictyo type are also found outside the Unikonta. They still occur in some groups of the Bikonta . This is the case with the alveolate ciliates (Ciliata) and with certain representatives of the Excavata ( Jakobida and the genera Naegleria , Trimastix and Malawimonas ). These bikonta could have obtained the dictyo-type α-amylases by horizontal gene transfers from the unikonta.

At the moment, it would also be possible to assume that the α-amylases of the dictyo type are actually not a feature of the Unikonta. Instead, they even represent a common characteristic of all eukaryota, i.e. all unikonta and all bikonta. The genes for this type of amylase would then have been lost much more frequently among the Bikonta than among the Unikonta, so that the α-amylases of the Dictyo type only appear today as a common derived characteristic of the Unikonta. At present, the taxonomic significance of the Dictyo-type α-amylases hardly seems to have been conclusively clarified. For this, much more extensive sequence comparisons seem necessary than can be carried out today.

Features microtubules

There are suspected three fine structural differences between the cells of the original Bikonta and the original Unikonta. All three differences are based on different occurrences and organization of the microtubules . Microtubules are tubular structures made of threads of the protein tubulin . Together with actins and intermediate filaments, they form the cytoskeleton . In addition, the centriol and the eukaryotic flagella consist of microtubules.

The cell of the last common ancestor of all Unikonta probably had a fairly symmetrical, conical, microtubular cytoskeleton. The microtubular part of the cytoskeleton is said to have looked completely different in the last common ancestor of all Bikonta. It is said to have been rather asymmetrical, with micotubular strands on the underside of the cell. From these two hypothetical starting forms all eukaryotic cell forms occurring today could have developed.

Different numbers of centrioles are assumed to be the second microtubular difference between Unikonta and Bikonta. Unikonta are said to have originally had one centriol per cell. Bikonta are said to have originally had two centrioles per cell.

The most important (and eponymous) microtubular difference between Unikonta and Bikonta is the flagellation . Unikonta probably originally had one scourge per cell. They were unikont . Bikonta probably originally had two flagella per cell. They were bicont .

In order to be able to address the microtubular differences in detail, the British biologist Thomas Cavalier-Smith works with very specific terms. Before this section of the text goes into the details, the terms should be introduced (and Germanized):

  • Uniciliaty ( uniciliaty ): A cell is uniciliat ( uniciliate ) when it carries a flagellum.
  • Biciliatie ( biciliaty ): A cell is biciliat ( biciliate ) if it has two flagella.
  • Multiciliatie ( multiciliaty ): A cell is multiciliaty ( multiciliate ) if it has many flagella.
  • Unicentriolarity ( unicentriolary ): A cell is unicentriolar ( unicentriolar ) if it contains a centriol.
  • Bicentriolarity ( bicentriolary ): A cell is bicentriolar ( bicentriolar ) if it contains two centrioles.
  • (Original) Unikonty ( unikonty ): The original unikonte ( unikont ) cell is said to have been both uniciliat and unicentriolar.
  • (Original) Bikontie ( biconty ): The original bikonte ( Bikont ) cell is both biciliat, may have been as bicentriolär.
  • Anterokontie ( anterokonty ): A cell is anterokont ( anterokont ) if the flagellum is anterior . Anterior flagella serve as draft flagella. A more common synonym for anterocontia is acrocontia .
  • Opisthokontie ( opisthokonty ): A cell is opisthokont ( opisthokont ), which is the scourge behind ( posterior ). Posterior flagella serve as thrust flagella.

The last common ancestor of all Unikonta living today was probably uniciliat and unicentriolar. His cell had a flagellum and a centriol. This corresponds to the original Unikontie and is still found today in some Amoebozoa , for example in the single-cell genus Phalansterium . The genus is also anterocontact. Your flagellum acts as a pulling scourge and sits at the front end of the cell. It is believed that the Unikonta were originally anterokont.

Within the Amoebozoa group, the anterocontal scourge was partially lost. The cells became akont, that is, flagelless. The development of acontia took place when a line of development completely changed to amoeboid locomotion with the help of pseudopodia . These flagellate, amoeba-like Amoebozoa are led under the group name Lobosa . Flagellated amoebozoa (Amoeboflagellaten) can be found recently within the other amoebozoa group of the Conosa . The Conosa include, for example, Phalansterium (uniciliat, unicentriolar), Multicilia (multiciliat, unicentriolar), various Archamoebae and also the slime molds (Eumycetozoa), whose gametes are often flagellated twice. The double flagellation makes the slime mold seem to move closer to the bikonta. However, their second scourge is seen as a convergent evolution to the biciliaty of the Bikonta. Because the gametes of the slime molds are biciliate unicentriolar (two flagella and one centriol per cell) and not biciliat bicentriolar, which would be expected in a real bicontia. With the genus Breviata ( Protamoebae / Breviatea ) there is also a form among the Amoebozoa that is uniciliatly bicentriolar. The bicentriolarity is achieved differently than with Bikonta. It is therefore probably a convergent evolution parallel to the Bikonta.

Within the Unikonta, the Opisthokonta form the sister group to the Amoebozoa. The cells of the opisthokonta no longer correspond to the original unicontal structure (unicentriolar), but represent a derived form: flagellated cell stages are unicentriolar, but also bicentriolar. The second centriol can be assessed as a newly developed characteristic of the opisthoconta. Furthermore, opisthoconta do not have an anterocontal traction flagella, but a posterior, opisthocontal thrust flagella. It is said to have emerged from the anterocontact scourge, perhaps as an adaptation to new food niches . The flagellation was also lost several times among the opisthokonta. Certain representatives of the Mesomycetozoa involved their flagellum in favor of amoeboid cell forms. In the multicellular animals ( Metazoa ) only the sperm, but not the egg cells, are flagellated. The loss of the flagellum among the chitin mushrooms ( Fungi ) is particularly noticeable . The vast majority of today's chitin fungi no longer form any flagellar-bearing cell stages and are therefore acontent. The best known exception to this are the unicellular flagella fungi ( potty fungi , Chytridiomycota). Their enthusiasts still show the original uniciliate, opisthoconous flagellation. Sometimes two swarmers merge with each other (therefore function as gametes ) and form planozygotes . These are zygotes that still carry the flagella of their two gametes for a while, that is, are double flagellated. From this original isogamy (fusion of two identical looking gametes) a certain group of flagella fungi has developed, the Monoblepharidales . With them only the male gametes are uniciliat, opisthokont flagellated. They swim to the large, immobile, acontent female gametes (egg cells). Most of the approximately 500 known species of flagella live in water, some in moist soils or as cell parasites in higher plants. In addition to them, there are other small groups of fungi with flagellated cells. These include the sister group of the flagella fungi, the Neocallimastigomycota , as well as the Blastocladiomycota and the genus Olpidium, which is systematically difficult to classify . In the Neocallimastigomycota the swarmers can be uniciliat, opisthokont or multiciliat. Like the flagella, the fungal genus Olpidium uniciliate, opisthocontal swarmers, which also function as gametes and generate biciliate planozygotes . In the Blastocladiomycota, the uniciliate, opisthokonten male gametes are slightly smaller than the flagellated female gametes ( anisogamy ). After merging , the zygote still carries the two flagella of the gametes (planozygote) for a short time. All of the scourge-bearing fungi mentioned above have in common that they occur in habitats with extensive water supply. Water is essential for flagellated locomotion. The flagellum stages were involved in the remaining fungi, often probably in the course of colonization of dry, terrestrial habitats.

Uniciliate bicentriolar cells are the hallmark of the opisthoconta. However, uniciliate bicentriolarity is also known from some organisms that have been phylogenomically identified as bikonta. These include, for example, the Pedinellales and some Prasinophyceae . For these forms of life it is assumed that their ancestors were originally really bicont (biciliate, bicentriolar), but lost the second scourge secondarily.

In contrast to the Unikonta, the last common ancestor of all today's Bikonta is said to have had two flagella (biciliaty) and two centrioles (bicentriolarity) per cell. Bicilia probably evolved in several steps. Initially, the cells probably moved with a uniciliate anterocontia. The pull scourge was then converted into a push scourge (uniciliate opisthocontia), perhaps as an adaptation to new food niches. Then a second, now anterior, flagella was placed on the opposite side of the cell and the old posterior flagellum was shortened. This form of flagellation (two flagella of different lengths) is also known as heterokont.

Parallel to the Unikonta, forms formed within the Bikonta in which the flagellation was completely involved (Akontia). This is the case with most of today's seed plants and probably happened in the course of increasing adaptation to terrestrial habitats: The seed plants (Spermatophytina) belong to the scion plants (Tracheophyta), a subgroup of the embryophytes (Plantae, Embryophyta), which together with certain green algae the Form the group of Charophyta ( Archaeplastida / Chloroplastida ). Charophytes also include candelabrum algae (Characeae). Your spermatozoids have two flagella that stand close together at the front end of the cell (draft flagella). The flagella have the same structure and length, so it is no longer the postulated, original heteroconous bicilia of the bikonta, but a derived isocontal bicilia. Very similar sperm are the mosses formed. They can also be found in the simplest shoot plants, the bear moss plants (Lycopodiophytina). In the ferns there are often flagellated spermatozoids. Similar multiciliate flagellated spermatozoids exist in the two evolutionarily old groups of seed plants, the ginkgo plants (Ginkgophyta) and cycads (Cycadophyta). All other seed plants do not form any flagellated cells. This acontia is a convergent evolution to the mushrooms, which are also mostly uncultivated.

Both the Unikonta and the Bikonta evolved multi-flagellated (multiciliate) forms. In the Unikonta, for example, the Amoebozoa Pelomyxa and Multicilia evolved the Multiciliatie from the original, uniciliate state. The best-known examples of the Bikonta are the alveolate ciliate animals (ciliata), which evolved from the original biciliate state.

The interpretation of the Multiliaty of the Protista genus Stephanopogon caused certain difficulties . The genus does not belong to the Unikonta, but phylogenomically clearly to the Bikonta ( Excavata / Discoba / Percolozoa / Percolatea ). However, it is multicilia and unicentriolar, similar to Pelomyxa and Multicilia (Unikonta / Amoebozoa). It is now assumed that the ancestors of Stephanopogon originally had a real bicontia. However, they later lost the second centriol, so that a secondary unicentriolarity occurred.

Characteristic microtubules: summary

  • Bikonta : originally biciliate, bicentriolar, heterocontact; asymmetrical microtubular cytoskeleton with ventral microtubule strands
    • Excavata
    • Chromalveolata
      • Pedinellales : derived from uniciliat, bicentriolar - convergence to the flagellum cells of the opisthokonta (Pedinellales however acrokont)
      • Ciliata : derived from multiciliate, bicentriolar - convergence to the swarmers of some Neocallimastigomycota
    • Archaeplastida
      • Viridiplantae
        • Chloroplastida
          • Prasinophyceae : some representatives derived uniciliat, bicentriolar - convergence to the flagellum cells of the Opisthokonta (Prasinophyceae however akrokont)
          • Charophyta
            • Characeae : Spermatozoids biciliat, bicentriolar, derived isocont - convergence to the planozygotes of the Chytridiomycota, Blastocladiomycota and Olpidium (spermatozoids of the Characeae but with flagella)
            • PlantsPlantae ( Embryophyta )
              • Mosses ( Paraphylum ): spermatozoids biciliate, bicentriolar, isocontal - convergence to the planozygotes of the Chytridiomycota, Blastocladiomycota and Olpidium (spermatozoids of the mosses but with flagella)
              • Tracheophyta
                • Lycopodiophytina : spermatozoids biciliate, bicentriolar, isocontal - convergence to the planozygotes of the Chytridiomycota, Blastocladiomycota and Olpidium (spermatozoids of the Lycopodiophytina but with flagella)
                • Euphyllophyta
                  • Monilophyta : Spermatozoids derived multiciliat, bicentriolar, isocont - convergence to the swarmers of some Neocallimastigomycota
                  • Spermatophyta
                    • Cycadophyta : Spermatozoids derived multiciliat, bicentriolar, isocont - convergence to the swarmers of some Neocallimastigomycota
                    • Ginkgophyta : Spermatozoids derived multiciliat, bicentriolar, isocont - convergence to the swarmers of some Neocallimastigomycota
                    • all other spermatophyta: derived akont - convergence to akonten fungi

Tribal history of the Unikonta in the Precambrian

The last common ancestor of all eukaryota should have had five separate genes for the enzymes carbamoyl phosphate synthase II, dihydroorotase, aspartate carbamoyltransferase, dihydrofolate reductase and thymidylate synthase. In one group of eukaryota, the genes for the first three enzymes fused while the genes for the last two enzymes remained separate. This group with the triple fusion were the first Unikonta. All of today's Unikonta descended from them.

The Unikonta genes for dihydrofolate reductase and thymidylate synthase are unfused. With all other Eukaryota, so with the Bikonta, however, they are united in a double fusion . That is why the Unikonta should have been the first group to split off from the rest of the Eukaryota. This happened deep in the Precambrian .

The oldest indications of eukaryotic life are biomarkers ( Cholestan ) from shale rocks of the Pilbara Kraton (Western Australia ). The schist comes from the Neo-Archean (Upper Archean ) and is approximately 2770 million years old. On the other hand, the earliest Unikonta fossils are from a genus called Tappania and are 1430 million years younger. It is very likely that the Unikonta first appeared much earlier, although there are no definite fossils in older rocks.

In order to be able to estimate the time of the first appearance of the Unikonta more closely, fossils from the Bikonta group help. There are some known fossils that are much older than Tappania and may be considered Bikonta. However, it is now also known that the Unikonta were the first to have separated from the other Eukaryota - i.e. from the later Bikonta. The time of this separation must therefore be set before the appearance of the first biconta fossils. If a Bikonta fossil is found, it must therefore be assumed that Unikonta were already present at the same time. However, these early Unikonta left no fossils or at least no fossils that can be clearly assigned to them: Perhaps there are also some Unikonta between the very heterogeneous , early Acritarcha .

The oldest known bikont could fossils of the genus Grypania from the Negaunee iron - Formation ( Michigan ) be. The formation dates from the Rhyacian (older Middle Paleoproterozoic ) and is approximately 2100 million years old. In Grypania it maybe was a eukaryotic alga and thus to bikont (more precisely Archaeplastida ). This assignment was made primarily based on the size of these spiral fossils, which are just over an inch long. On the other hand, it could be with Grypania. also acted around chain-shaped colonies (similar to today's Anabaena ) from particularly large bacteria . The largest cells of today's bacteria reach a diameter of up to 0.75 mm ( Thiomargarita namibiensis ).

The oldest acritarcha, which can be identified with some certainty as Eukaryota, come from the Chuanlinggou Formation (northern China ). The formation dates from the Statherian (Upper Paleoproterozoic ) and is approximately 1730 million years old. The acritarcha in question are egg-shaped microfossils .

The oldest trace fossils , which presumably go back to Bikonta, are in the Chorhat sandstone ( India ). The sandstone comes from the Statherium (Upper Paleoproterozoic ) and is between 1632 and 1628 million years old. The trace fossils look as if worm-like creatures have crawled over the sand. However, it is more likely that they were pulled by large unicellular organisms . For example, off the Bahamas, at a depth of 750 m to 780 m, it was observed that the giant amoeba Gromia leaves very similar traces on the sea floor. Gromia. is counted to the Bikonta (more precisely Rhizaria ). If the trace fossils of Chorhat should actually come from living beings that were close to today's Gromia giant amoeba, Bikonta (and thus also Unikonta) would have existed as early as 1632 million years ago.

The earliest fossils that date back with some certainty on unikont, come from a benthic living genus called Tappania . Hyphae are seen in the fossils , so Tappania was likely a fungus. The fungal plexuses were found in both the Wynniatt Formation ( Victoria Island , Northwest Canada ) and the Roper Group ( Australia ). The finds come from the Upper Calymmian (lower Mesoproterozoic ) and are approximately 1430 million years old. The cell walls of a fungal network are made of chitin . Therefore it can fossilize relatively easily. For this reason, the fungi could be the first Unikonta to appear in the fossil record. The Unikont Tappania is about 230 million years older than the first truly undisputedly identifiable bicont called Bangiomorpha pubescens . This red alga was found in the Hunting Formation ( Somerset Island , Canada). The formation comes from the oldest stenium (Upper Mesoproterozoic) and is about 1200 million years old.

The second group of Unikonta are the Amoebozoa. The oldest amoebozoa fossils to date are so-called vase-shaped microfossils (VSM). These microfossils are very reminiscent of Thecamoebs . VSM were recovered from the Grand Canyon and are between 736 and 748 million years old from the Cryogenian (Middle Neoproterozoic).

The third important group of Unikonta are the animals . The oldest evidence for the presence of Animalia is from the steroid 24-isopropyl cholestane . This biomarker is now produced by a group of sponges ( Demospongiae ). The steroid was discovered in southern Oman in sediments that originate from the Cryogenium (Middle Neoproterozoic ) and are at least 635 million years old. Also Rhizarien are biosynthesise able predecessor molecules to 24-Isopropylcholestan, which means that this molecule is not a clear indicator of animals.

According to a very extensive, current phylogenomic study, the Animalia (animals) are divided into Choanoflagellata and Metazoa . The Metazoa are divided into Porifera (sponges) and Placozoa + Eumetazoa . The Eumetazoa are divided into Coelenterata ( Ctenophora and Cnidaria ) and Bilateria ( Protostomia and Deuterostomia ).

Because the biomarkers come from Demospongiae (Porifera), the animal Unikonta should have split at least twice by this time. Once in Choanoflagellata and Metazoa and the latter again in Porifera and Placozoa + Eumetazoa.

Certain microfossils from the phosphorites of the Doushantuo Formation (southwest China ) have long been regarded as the next most recent evidence of animal life. The formation comes from the middle Ediacarian (upper Neoproterozoic ) and is around 590 million years old. The microfossils were interpreted as eggs and early embryonic stages of various animals. However, there are strong arguments in favor of seeing them as remnants of large sulfur bacteria . In the phosphorites of the Doushantuo Formation there are other fossils, the interpretation of which is indisputable. These are fossils of early Porifera (more precisely Demospongiae) and soft tissue fossils of early Coelenterata (more precisely Cnidaria / Anthozoa / Hexacorallia / Tabulata ). Based on the current findings, it could be said that of all tissue animals living today, the recent Anthozoa should resemble the first Eumetaza most closely.

The first fossil records for Bilateria are a little more recent, come from the Upper Ediacarian and are between 542 and 560 million years old. These fossils are all flattened worm-like and are only a few inches long. Among the most prominent representatives include Spriggina (possibly Protostomia) Kimberella (possibly Protostomia) Ernettia (possibly Deuterostomia) and a still unnamed fossil from the Flinders Ranges (South Australia ) that much of Chordata recalls and South Australian Museum in Adelaide will be issued .

Summary of the tribal history of the Unikonta in the Precambrian

Individual evidence

  1. ↑ a b c A. Stechmann, T. Cavalier-Smith: Rooting the Eukaryote Tree by Using a Derived Gene Fusion. In: Science . 297, 2002, pp. 89-91.
  2. ↑ a b F. Burki, K. Shalchian-Tabrizi, M. Minge, Å. Skjæveland, SI Nikolaev, KS Jakobsen, J. Pawlowski: Phylogenomics Reshuffles the Eukaryotic Supergroups. In: PLoS ONE 2. 2007, p. E790.
  3. ↑ a b D. Moreira, S. vd Heyden, D. Bass, P. López-García, E. Chao, T. Cavalier-Smith: Global eukaryote phylogeny: Combined small- and large-subunit ribosomal DNA trees support monophyly of Rhizaria , Retaria and Excavata. In: Mol. Phylogenet. Evol. 44, 2007, pp. 255-266.
  4. ↑ a b c d e f g T. Cavalier-Smith: Megaphylogeny, Cell Body Plans, Adaptive Zones: Causes and Timing of Eukaryote Basal Radiations. In: Journal of Eukaryotic Microbiology. 56, 2009, pp. 26-33. PMID 19340985 .
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