OUR EVOLUTIONARY LINEAGE

OUR ANCESTRAL TREE

From several chapters of my 2010 unpublished manuscript, Evolution Insights, I have pieced together the following direct lineage leading back to our protozoan ancestors.  Within the groups listed were many other groups ancestral to side branches making up an evolutionary tree of life.  Implied for the lineages within each group is a vast continuum of extinct species from those much as in the preceding or subsequent phyla or groups named.

CHORDATA
                                          Humans
                                          Hominoids
                                          Monkeys
                                          Primitive Primates [extinct]
                                          Insectivorus mammals
                                          Early mammals [extinct]
                                          Therapsid reptiles [extinct]
                                          Stem reptiles [extinct]
                                          Labrinthodont amphibians [extinct]
                                          Crossopterygian fishes
                                          Jawed fishes
                                          Agnatha
                                          Cephalochordata
HEMICHORDATA           Hemichordata
ANNELIDA                      Pogonophora
                                          Polycheata
[hypothetical]                     [Protonemertean][extinct]
PLATYHELMINTHES     Triclad turbellarian
CNIDARIA                       Hydrozoans
                                          Tetracorals [extinct]
                                          Tabulate corals [extinct]
PORIFERA                       Sclerosponges
                                          Simple sponges
PROTISTA                       Choanoflagellates
PROTOZOA                    Amoeboflagellates

A Time Scale of events associated with the above transition in reverse order beginning with the formation of elements in the universe follows the first seven below.  [bya = origin in billion of years ago;  mya = origin in millions of years ago]

Item or adaptation       -       Origin       -       Group

Elements                               > 12 bya
Ammonia, water, methane     > 4 bya
Amino acids, small organic molecules    ~ 4 bya
RNA, DNA, organic membranes          ~ 4 bya

Early cells    -     ~ 3.5 bya      -                bacteria
Photosynthesis     -     ~ 2.5 bya    -       photosynthetic bacteria
Chromosomes, nucleus, sex     -     ~ 2 bya     -     amoeboid protozoans
Cells with mitochondria and flagella    -    < 2 bya    -    amoebas, flagellates
Amoeboid and flagellated cells in colonies -  ~ 1.5 bya  -  Choanoflagellates

Extracellular skeletal fibers, spicules  -  < 1.5 bya   -   Porifera (sponges)
Sponges with massive carbonate base   -      < 1.5 bya   -    Sclerospongea
Nerves, muscles, gut      -     ~ 1 bya    -     Anthozoa
Manubrium, rhopalium     -    ~ 1 bya    -    Hydrozoa
Head, bilateral symmetry, sex organs   -    ~ 1 bya   -    Triclad flatworm
Blood vessels, anus     -       ~ 1 bya    -   [protonemertean]
Segmentation/metamerism, nephridia   -  ~ 1 bya  -  Polychaete annelids
Loss of segments, gut, & spiral cleavage    -    ~ 1 bya   -    Pogonophora
Gut restored, gill slits     -     < 1 bya     -      Hemichordates
Notochord    -    ~ 0.5 bya    -    Cephalochordates (first chordates)

Cartilaginous skeleton, vertebrae     -     ~ 0.5 bya    -       Agnatha
Jawed fish, bony skeleton     -      > 400 mya    
Lungs, fleshy fins          -       > 400 mya     -      lungfish
Four fleshy fins      -    ~ 400 mya      -      -     crossopterygians
Four bony legs, three chambered heart    -    ~ 400 mya    -      amphibians
Shelled egg, internal fertilization      -     ~ 300 mya    -     reptiles
Hair, large brain, warm-blooded     -     ~ 200 mya    -    mammals
Arboreal insect eaters, clawed   -   ~ 150 mya   -   insectivorous mammals

Arboreal fruit eaters, nails     -     ~ 70 mya     -     primates
Large size and brain, loss of tail    -     ~ 40 mya    -    apes
Upright posture, brain volume increases   -    ~ 20 mya      -   hominoids
Primitive humans, still larger brains     -    ~ 4 mya    -    Australopithecus
Modern humans, brain doubles  -  > 40,000 B.C.  -  Homo sapiens

    [protonemertean] is a suggested line of near relatives of nemerteans

The polychaetes were the protostomes that gave rise to deuterostomes through the Pogonophora as discussed in previous posts of last year.
The polychaetes also gave rise to all the advanced protostomes such as arthropods and mollusks through other lineages not shown here (see earlier posts on arthropods and mollusks).

The view above is at odds with the mistaken impression in recent literature which accepts two erroneous groups, including one that places nematodes in an untenable ancestral position for several phyla.  The mainstream position of sponges is seldom recognized nor is the simple transition from sponges to cnidarians to flatworms then nemerteans.  I expect my peers will be unable to comprehend the above until they grasp the extreme longevity of deep sea ancestors.  I take sole responsibility for any errors in these comments and tend to leave off my title of Emeritus Professor of Biological Sciences, Western Michigan University, Kalamazoo, Michigan - to avoid being a source of embarrassment for such a fine institution and for those who were my students.

Joseph G. Engemann           December 9, 2014