Neomura Totally Explained

Neomura is a speculative clade composed of the two domains of Archaea and Eukaryota. The group was first proposed by Thomas Cavalier-Smith and its name means "new walls"; so called because it's thought to have evolved from Bacteria, and one of the major changes of this evolution was the replacement of peptidoglycan cell walls with other glycoproteins. The adjectivial form is Neomuran, and a single individual from the group is called a Neomuran.
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Morphology

The Neomura are a very diverse group, containing all of the multicellular species, as well as all of the most extremophilic species. However, certain characteristics are shared among them. All Neomurans have histones to help with chromosome packaging, and most have introns. All use the molecule methionine as the initiator amino acid for protein synthesis (Bacteria use formylmethionine). Finally, all Neomurans use several kinds of RNA polymerase, whereas Bacteria use only one. The common characteristics of the Neomura are all molecular.

History of Taxon

When Carl Woese first published his three-domain system, it was believed that the domains Bacteria, Archaea, and Eukarya were equally old, and that they were equally related on the tree of life. However, certain evidence began to point to a relationship between Eukarya and Archaea, and that both were more closely related to each other than either was to Bacteria. This evidence included the common use of cholesterols and proteasomes in Archaea and Eukarya, both of which are complex molecules not found in most bacteria. So, it was thought that there were two branches of life: Bacteria, and Neomura.
Recently, though, Cavalier-Smith has provided evidence to support the theory that Neomura and Bacteria are not separate branches, and that in fact, Neomura evolved from Bacteria. The biggest argument for this theory is that if eukaryotes are as old as bacteria, and the eukaryotic mitochondrion is derived from an alpha-proteobacteria (a highly evolved group of bacteria), then there must be several groups of eukaryotes that evolved before the endosymbiosis of the mitochondrion. This isn't so, and it's very unlikely that Eukarya didn't branch in the many millions of years it took for bacteria to evolve the aerobic respiration performed by mitochondria. It is known almost for certain that the mitochondrion derives from a bacteria, so therefore, eukaryotes must be younger than bacteria.
Another less major, but still important, piece of evidence is that the cholesterols and proteasomes found in Neomura are also found in the Actinobacteria, perhaps the most highly evolved bacteria. Molecules of this complexity are unlikely to evolve more than once in separate branches, so it follows that Neomura evolved from the very top of the bacterial tree. This particular theory of Neomuran evolution is shown in the image to the right.

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