Plants, Unikonts, Excavates and SARs

Posted on January 23, 2008  Comments (2)

image of 4 biology supergroups

The Tree of Life Has Lost a Branch

“The results were pretty astounding. All non-bacterial life on Earth – called eukaryotic life – can now be divided into four main groups instead of the five groups that we have been working with up to now,” says Kamran Shalchian-Tabrizi, an associate professor from the University of Oslo’s Department of Biology

All life on Earth can be divided into two essentially different life forms—eukaryotes and prokaryotes. The eukaryotes gather their genetic material in a nucleus, while the prokaryotes (bacteria and archaea) have their genetic material floating freely in the cell. Eukaryotic organisms—such as humans—can, as a result of the new findings, be divided into the following four categories:

  • Plants (green and red algae, and plants)
  • Opisthokonts (amoebas, fungi, and all animals—including humans)
  • Excavates (free-living organisms and parasites)
  • SAR (the new main group, an abbreviation of Stramenophiles, Alveolates, and Rhizaria, the names of some of its members)


Three billion years ago, there was only bacteria and Archaea. Eukaryotic life, which comprises all multi-celled organisms, developed in the sea—probably between 1.2 and 1.6 billion years ago. It was not before about 500 million years ago that the first creatures crept onto land.

Related: research article Phylogenomics Reshuffles the Eukaryotic SupergroupsEvolution is Fundamental to ScienceThe Decline and Fall of the Animal Kingdom

2 Responses to “Plants, Unikonts, Excavates and SARs”

  1. Curious Cat Science and Engineering Blog » All present-day Life on Earth Has A Single Ancestor
    June 21st, 2010 @ 10:30 am

    [...] All present-day life arose from a single ancestor All life on Earth shares a single common ancestor, a new statistical analysis confirms. … Because microorganisms of different species often swap genes, some scientists have proposed that multiple primordial life forms could have tossed their genetic material into life’s mix, creating a web, rather than a tree of life. … A universal common ancestor is at least 102,860 times more probable than having multiple ancestors, Theobald calculates. … For his analysis, Theobald selected 23 proteins that are found across the taxonomic spectrum but have structures that differ from one species to another. He looked at those proteins in 12 species – four each from the bacterial, archaeal and eukaryotic domains of life. [...]

  2. Exploring Eukaryotic Cells » Curious Cat Science Blog
    March 4th, 2012 @ 11:24 pm

    This webcast is packed with information on the makeup and function of eukaryotic cells, which are the type of cells found in animals. It is part of a interesting series of science webcasts…

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