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

UNRECOGNIZED PRINCIPLES OF EVOLUTION

HELP NEEDED - TELL YOUR FRIENDS - SEND A LINK

Any biologist doing evolution type studies of phylogeny should understand the concepts of the following posts which are not currently appreciated, especially by those doing molecular phylogeny studies.

June 9, 2014, Variable rates of evolution

http://evolutioninsights.blogspot.com/2014/06/variable-rates-of-evolution.html

June 22, Evolution in the deep sea

http://evolutioninsights.blogspot.com/2013/06/evolution-in-deep-sea.html

http://evolutioninsights.blogspot.com/2013/06/evolution-protostome-deuterstome-link.html

May 31, 2013 or June 1, 2013  Science screw-up no. 1 - Why molecular phylogeny experts have gone astray with the introduction of Ecdysozoa and Lophotrochozoa has been archived as below

http://evolutioninsights.blogspot.com/2013_05_01_archive.html

January 23, 2015 -  Salvaging data for evolution studies, it should be read in conjunction with the blog post listed above, may be a view principally of interest to biologists studying evolution.

http://evolutioninsights.blogspot.com/2015/01/salvaging-data-for-evolution-studies.html

IF YOU KNOW A BIOLOGIST THAT RESEARCHES IN EVOLUTIONARY STUDIES PLEASE EMAIL HIM A LINK TO THIS POST

http://evolutioninsights.blogspot.com/2015/01/unrecognized -principles-of-evolution.html

My demise is not expected, but at my age I would hate to leave a world lacking a link to ideas needed for the advance of animal evolution studies.

Joseph G. Engemann   Kalamazoo, Michigan   January 24, 2015

ANIMAL KINGDOM EVOLUTION

THE MAJOR GROUPS

The roots of the animal kingdom and other kingdoms are closely intertwined prior to the origin of multi-cellular plants and animals.  We think the earliest organisms are still represented today by the bacteria and other forms lacking a nucleus in their membrane-enclosed selves.  During this stage, perhaps the first billion years of evolution, the basic biochemistry of life evolved.  The RNA, DNA, and much of the basic materials still found in subsequent organisms evolved.

A consequence of the development of photosynthetic organisms in the world, then lacking oxygen in the atmosphere, was the production of oxygen as a toxic waste product that accumulated and changed the biosphere for the remaining time on earth.  Some of the early organisms developed the ability to utilize oxygen to oxidize organic material for their energy.  They could then remain active in the absence of light while extracting more energy from food than was possible by anaerobic process alone.  

Organisms that protected their genetic material from the oxygen with a nuclear membrane could better survive as oxygen reached higher levels.  Some developed a symbiotic relationship with other organisms.  Details of these early steps are discussed by Lynn Margulis (1981, Symbiosis in Cell Evolution, W. H. Freeman and Co., New York).  The evidence that mitochondria of our cells are a result of symbiosis is very strong; perhaps cilia are derived from flagella that also came from a similar symbiotic origin.

At this stage of evolution the Animal Kingdom or its one-celled progenitors, the Protozoa, had representatives so overlapping with plants and fungi that many biologists prefer to put them in a separate kingdom, the Protista.  These early steps were developing during the second billion years of life on earth.

By the beginning of the third billion years on earth a protozoan that could change back and forth from one with a flagellum to one with pseudopodia had evolved.  Sometime the pseudopodia would develop into a collar around the flagellum.  Eventually some of these dual potential cells stuck together and developed small colonies that eventually specialized into sponges.  The single cell with the capacity for diverse structure and a mechanism for controlling it needed a few control changes in a few different cells of the colony to provide the basic material for evolution of many of the features of all animals.

The Porifera were the first phylum of animals to develop.  They diversified into many different sponge types until one group gave rise to coral-like animals as indicated by the similarity to a Middle Devonian anthozoan (Kazmierczak, Jozef. 1984.  Favositid tabulates: evidence for poriferan affinity.  Science, 225:835-837.).  

Recognition of this evidence of anthozoans as the first cnidarians provides a basis for a simple continuity of phyla in the early stem of animals leading to the next phylum, the Platyhelminthes which may be considered the earliest protostomes.  A simple but unconventional view is that anthozoan polyps gave rise to jellyfish ancestral to triclad planarians.  The complexity of the simple process is why I needed to write my manuscript, Evolution Insights, to make it evident.

The sponges have less well-defined tissues than phyla that follow.   But the main mass of sponge is jelly-like with a few amoeboid cells and a tangle of collagen-like fibers and is much like loose connective tissue in our own bodies.  The jelly-like mass is mostly covered with flattened cells and is perforated by many pores leading to canals and or cavities lined with choanocytes.  Choanocytes are cells with a flagellum surrounded at the base with a collar that collects microscopic food items to nourish the sponge.  Water is passed out one or a few large openings.  Most sponges have spicules.  Spicules are mineralized (calcareous and/or siliceous), often needle-like, or three-pointed and other shapes often specific to the class of the sponge.

The protostomes included all the animals above the cnidarians until the deuterostomes evolved.  The seemingly hidden origin of deuterostomes becomes simple and clear when the role of the Pogonophora is known.  The next several blogs are expected to deal with the origin of the deuterostomes.  Then it will be time to clarify the Porifera-Cnidaria-Platyhelminthes links.  Later, the origin of mollusks and arthropods from annelids will be covered.  The foggiest portion of animal evolution, Platyhelminthes to Annelida, is obscure because the intermediate steps left neither a fossil nor living close relative to my knowledge. 

The annelids seem to be the living representatives of the most ancient animals with a true coelom, a body cavity with body wall lined with a cellular layer of flattened cells.  Organs enclosed in the coelom are also covered with a similar cellular layer; the two layers often connect to form a double layered mesentery.  The mesenteries may help keep organs in position, including blood vessels and nerves servicing them.  Of the simple animals, more complex than flatworms, but still lacking both a true coelom and segmentation (or its derivative, metamerism), although having characteristics more in common with advanced animals, we find only the nemerteans.

The protostomes including flatworms, nemerteans, annelids, mollusks, and arthropods get their name from the embryonic origin of the mouth from the blastopore.  The first (proto-) opening becomes the mouth (-stome), thus their name Protostomia.  In deuterostomes a second embryonic opening or region becomes the mouth.  The deuterostomes include hemichordates, chordates, and echinoderms.

Besides mouth origin, major contrasts between major phyla of the two groups (advanced protostomes and deuterostomes) include spiral versus radial cleavage, determinate versus indeterminate cleavage, presence or absence of chitin.  A minor phylum, the Pogonophora, blurs these and other distinctions and gives good reason to be the link between the two branches of higher animals.  To me, the evidence is so good any other proposals lack standing.  

An earlier post (SCIENCE SCREW-UP NO. 1) provides reasons the currently popular view of phylum relationships is incorrect.  Most of my immediately following posts will address various aspects of the origin of deuterostomes.  

Joseph G. Engemann, Emeritus Professor of Biology, WMU, Kalamazoo.  6/20/2013