9.IX: Human Ancestor Image Gallery

These organisms are close representatives of what your ancestors looked like at critical stages of development.  Each successive taxon is a subset of the previous one, and humans belong to every taxon represented here.  That is, a human is a eukaryote, an opisthokont, an animal, etc., continuing to an amniote in this chapter of development.

2 BYA: Endosymbiosis.  Alpha-proteobacteria (small, left) took residence in host archaea.  Together, they became the first eukaryotic cells, and the bacteria became mitochondria.  Here, the prokaryote and eukaryote are shown roughly to scale. 12
800 MYA (?): Our last unicellular ancestors were opisthokonts, from which sperm cells take their form.  Sponges only have a few cell types, one of which looks like this. 3
800 MYA (?) 4 :  The first animal was the sponge; many varieties are shown here. The “mouths” are not for feeding, as food is absorbed through the entire body.  5
800 MYA (?): The first metazoa was just a single layer of skin with a mouth that was used for feeding and excreting waste. 6
700 MYA (?) 7 : The deuterostome developed a more complex interior, including a through gut with anus. 8
600 MYA (?) 9: The first chordate was a “fish shell” with no eyes, heart, or brain. 10 This poor creature should have followed Dorothy to see the Wizard. 11
500 MYA: The first vertebrates made major advances in organ structure and may have been the first conscious creatures. 12
400 MYA:  Because we are gnathostomes, we have a face – two eyes, two nostrils, and a jaw. Let’s be glad faces have gotten prettier since they first appeared on this armored fish, the placoderm. 13
350 MYA: Tetrapods spent tens of millions of years at water’s edge, gradually going through the major adaptations required for life on land.  This species, Pederpes finneyae, is the first known animal with five-toed limbs. 14
> 300 MYA: As amniotes, we are fully adapted to the terrestrial environment. 15

Back to Section 9.VIII:  Chapter 9 Summary



Skip to Chapter 8 Human Ancestor Image Gallery

  1. Mitochondria photo:  National Institutes of Health (public domain), https://commons.wikimedia.org/wiki/File:Mitochondrion_186.jpg (accessed and saved 8/21/19).
  2. Amoeba photo: By Cymothoa exigua (Own work) CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0), https://commons.wikimedia.org/wiki/File%3AAmoeba_proteus.jpg (accessed and saved 6/24/15). Composite image by Scot Fagerland, 8/22/19.
  3.  Opisthokont photo: By Stephen Fairclough, CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5) or CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5), https://commons.wikimedia.org/wiki/File%3AMonosiga_Brevicollis_Phase.jpg (accessed 6/24/15)
  4. C.K. “Bob” Brain et al., “The first animals: ca. 760-million-year-old sponge-like fossils from Namibia”, South African Journal of Science vol. 108 no. 1 / 2 (1/18/2012), http://archive.SAJS.co.za/index.php/SAJS/article/view/658 (accessed and saved 8/10/19).
  5.  Sponge photo by Twilight Zone Expedition Team 2007, NOAA-OE. (NOAA Photo Library: reef3859).  Public domain.
  6.  Comb jellyfish photo by NOAA / OAR / National Undersea Research Program (NURP), http://www.photolib.noaa.gov/htmls/nur01002.htm, public domain.
  7. Francisco José Ayala, Andrey Rzhetsky, and Francisco J. Ayala, “Origin of the metazoan phyla: Molecular clocks confirm paleontological estimates,” PNAS 95(2):606-611 (1/20/1998), http://www.pnas.org/content/95/2/606.long (accessed and saved 8/10/19).
  8.  Sea cucumber image by NOAA, http://flowergarden.noaa.gov/image_library/inverts/threerowedcucumberelh.jpg , public domain.
  9. Francisco José Ayala, Andrey Rzhetsky, and Francisco J. Ayala, “Molecular Clocks and the Origin of Animals”, in S.P. Wasser (ed)., Evolutionary Theory and Processes: Modern Perspectives, Kluwer Academic Publishers (1999) pp. 151-169, https://link.springer.com/chapter/10.1007%2F978-94-011-4830-6_10 (accessed and abstract saved 8/10/19).
  10. J.K. Sky Yu and Linda Z. Holland, “Cephalochordates (amphioxus or lancelets): A model for understanding the evolution of chordate characters,” Cold Spring Harbor Protocols 2009, http://cshprotocols.cshlp.org/content/2009/9/pdb.emo130  (introduction accessed and saved 8/10/19).
  11. Lancelet image by Hans Hillewaert, via Wikimedia Commons, https://commons.wikimedia.org/wiki/File%3ABranchiostoma_lanceolatum.jpg (accessed and saved 7/02/15) 
  12. Image of Myxinikela siroka by Nobu Tamura, email:nobu.tamura@yahoo.com  http://spinops.blogspot.com/ http://paleoexhibit.blogspot.com/ (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:Myxinikela_NT_small.jpg (accessed and saved 8/21/19).
  13.  Placoderm illustration by Nobu Tamura (http://spinops.blogspot.com) (Own work) GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY 3.0 (http://creativecommons.org/licenses/by/3.0), via Wikimedia Commons, https://upload.wikimedia.org/wikipedia/commons/9/95/Dunkleosteus_BW.jpg (accessed 6/20/15)
  14. Tetrapod image by DiBgd at the English language Wikipedia, license GFDL or CC-BY-SA-3.0, https://commons.wikimedia.org/wiki/File%3APederpes22small.jpg (accessed 7/02/15)
  15.  Amniote (casineria) illustration by ДиБгд (Own work) (CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)), https://commons.wikimedia.org/wiki/File%3ACasineria_kiddi_reconstruction.jpg
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