THE TREE OF LIFE

REVISED TREE OF LIFE

The revised tree of life described in the previous post lacked any illustration to aide understanding.  The transfer of files to a new computer, operating system and associated software (Windows Vista to Windows 10) has delayed production of something suitable.  I was eventually able to find Paint embedded in 10.  But my attempt to modify the diagram below with color to clarify the protostome and deuterostome groupings left an illustration dangling somewhere in a jpg file that I have not been able to migrate to this blog.

 The protostomes began with platyhelminthes, the flatworms ancestral to other protostomes, and eventually deuterostomes via annelids.  The anthropocentric view showing primates upper right as the ultimate chordates is only for illustration of our lineage.  Every living group could have an illustration showing their group at the peak.  Some hint of this is shown with wasps and flies being groups of insects at the upper left.  And at the far left the cephalopods are perhaps the ultimate mollusks.

The boldface names in the above diagram represent groups in the direct ancestral line to primates.  All animals with a eucoelomate body cavity are included in the annelids and those above them in he diagram.  Phylum names are in all capital letters.  Polychaetes are probably the ancestral annelids for other annelids (oligochaetes and their descendants the leeches), mollusks, and arthropods, as well as the pogonophorans.  Echinoderms and lophophorates were probably each derived from ancestors intermediate between polychaetes and hemichordates; echinoderms perhaps being farther along the line to chordates in their origin.

The various other groups are not all fairly treated in showing how advanced they are in an evolutionary sense.  Their position is generally more an estimate of the antiquity of their origin.

OLDER VERSIONS OF THE TREE OF LIFE

A.  Prior to the erroneous Lophotrochozoa and Ecdysozoa proposals the "Tree of Life" would have looked much like the version presented above with the following evident.
 1. a separate origin of the deutrostomes from much earlier connecting the Hemichordates via unknown intermediates to the platyhelminthes.
2. a consequence is the assumption of a separate origin of coelom and blood vascular system of deuterostomes and advanced protostomes.
3. inexplicable cellular, histological, and moleular similarities in advanced protostomes and deuterostomes.

B.  The Lophotrochoza error may some value as an assessment of lophophorate invertebrates but is not much use as showing relationships to vertebrates and some other phyla.

C.  The Ecdysozoa error is made worthless by trying to make nematodes an important part of the evolutionary history of other some other phyla.  Nematodes, as partially indicated in the diagram above, are probably part of an aschelminth group derived from turbellarian flatworms miniaturized by selection for adaptation for life in the interstices of marine, then freshwater and terrestrial sediments.  The extreme specialization of nematodes did not provide a good base for selection of new groups.  The superficial resemblance of their outer covering with the exoskeleton of arthropods is misleading.  Surprisingly or fortunately, they did not make reptiles part of the group for shedding their skin.  The post of May 31, 2013 should make it evident why the molecular data they used as a basis for Ecdysozoa is worthless.

D.  Other versions of the "tree of life" based on symmetry and other features such as segmentation are not in vogue today, although the data used for them may have application in limited portions of "the tree of life".  The antiquity of brachiopods and bryozoans as well as considerable differences in the lophophores would seem to argue for separate origins, perhaps from somewhere along the polychaete to pogonophora line.

E.  The ancient annelid theory (over 100 years old) can be tweaked by insertion of the pogonophora to explain several things as shown elsewhere in the blog and indicated by the above diagram.
1. How the pogonophora turned an annelid arrangement of systems in to the chordate pattern.
2. How the anterior nervous system could fuse into a brain without an esophagus penetrating it.
3. How the drastic embryological changes of spiral to radial cleavage were simply made.
4. How molecular homologies of chordates and advanced protostomes came about.


Joseph G. Engemann   Emeritus Professor of Biological Science, Western Michigan University, Kalamazoo, Michigan     May 16, 2016

Disclaimer: All errors, mistakes, and omissions are my own and not the responsibility of Michigan State University, The University of Tasmania, nor Western Michigan University, nor the U. S. Fulbright Agency; although their assistance was valuable enabling me to make them.  jge