THE MAJOR EVOLUTIONARY TRANSITION

Annelid worms are ancestral to all of the advanced major phyla.  Arthropods and mollusks retained annelid features as one major grouping of advanced phyla.  Chordates and echinoderms are the other major grouping.  The two groups share some common feature as a result of their annelid ancestries.

There are eight posts in this blog-site from 6/17/13 to 6/30/13 that are a more extended description of the basis for accepting the annelid theory of chordate origin.  The annelid theory eliminates the need to (1) assume a second early origin of segmentation and/or metamerism from acoelomate protostomes, (2) explain numerous bits of molecular similarity between coelomate protostomes and deuterostomes, (3) and, with the incorporation of information about the pogonophoran bottleneck connection provided in this blog, provides a logical rationale for the embryological differences as well as the mechanism of inversion of systems in the transition of protostomes to deuterostomes.

THE ANNELID PHASE

The pogonophora are fairly well established as close relatives of some marine polychaete annelids.  The fossil record provide very little evidence of events, but some annelid descendants clearly  existed during the pre-Cambrian.

Step one.  Tube-dwelling worms such as Sabella, started the rotation as they reoriented their posterior to a position in the sediments and left their plumose tentacles up in the water.

Step two.  Those becoming pogonophorans had multiple changes selected by the rigor of life at constantly increasing depths as they struggled to survive asteroid bombardments in the pre-Cambrian.  In particular, low metabolic rates due to abyssal pressure and temperature, tubes extending deep into the sediments for absorption of fossil nutrients, as well as retention of a blood vascular system to transfer oxygen from the water to the embedded end of the worm deep in the sediments, and loss a many non-essential features.  The thinning of the eggshell enabled dropping the spiral development of annelids and the ability of eggs to develop even if some cells were lost.  Loss of obvious segmentation left only a remnant of segments at the  posterior to anchor the worm in its tube.

Part  of step two was the reduction of the digestive system, particularly the mouth and esophagus.  This allowed the later fusion of the ganglia of the head into a brain blocking the mouth formation on the old ventral side.

Step three.  As asteroid caused extinctions in the surface areas of the oceans eased, progeny of the abyssal worms survived as they moved into shallow water and benefited by mouths developing where gut remnants touched epidermis on  the old dorsal side.  As they extending from their tube they now would use their relocated mouth to feed on particulate matter in their vicinity.

Step four.  As they increased their activities they were doing it with the old dorsal side now the new ventral side.  SO THE WORMS DID NOT ROLL OVER, THEY DID A BACK-FLIP as they made their transition from annelid to pre-Chordate organisms during the pre-Cambrian.

Referring to the February 27, 2015 post on "Evolution: the body cavity" may help you understand the bit about relocation of the mouth above.  The March 2, 2015 post on "Abandoned theories and Libbie Hyman"  has a brief discussion of the annelid theory and an associated figure.

THE IMPORTANCE OF THE REGRESSIVE  POGONOPHORAN STEP

The loss of features as pogonophorans adapted to life in the deep sea were essential factors enabling the climb to the branch of the animal kingdom known as the deuterostomes, with the vertebrates members dominating life on earth.  It enabled rearrangement of the head with fusion of ganglia into a brain and mouth formation on the former dorsal surface, simplified embryology of radial cleavage and delayed determination of first cells of the embryo.  The loss of ability to form chitin in deuterostomes meant other structural materials became more important.  Hemoglobin is the only blood pigment surviving in deuterostomes although a diversity of blood pigments are found in annelids prior to the pogonophorans.

OTHER PHYLA

There are other major and minor animal groups that are side shoots at many positions along the groups of the tree of life leading to as well as following the significant deuterostome branch.  They continued, some becoming extinct, others diversifying into forms still present.  One major group of arthropods, the trilobites, dominated paleozoic seas before becoming extinct.  The sponges of today no longer include the group giving rise to early protostomes.

The above figure shows the central sequence of protostomes leading to annelids from which all above them trace their ancestry and have coelomate body cavities.  The sequence follows a time sequence of origin of groups having living representatives (except for the hypothetical protonemerteans).  The pogonophorans provide a transition from coelomate protostomes to the vertebrate line that clarifies the transition without the mystery of many unknown ancestral groups coming from flatworms.

Many invertebrate groups such as ctenophorans, chaetognathans, lophophorates, echinoderms, sipunculids, extinct groups, and many others are not represented in the diagram.

Joseph Engemann   Emeritus Professor of Biology, Western Michigan University, Kalamazoo, Michigan      July 16, 2018

REORGANIZING THE TREE OF LIFE

THE MAJOR STEP NEEDED

The major line of animal evolution, known as deuterostomes and including chordates, hemichordates, and echinoderms, needs  to be recognized as having its origin in the early annelid worms via a group of polychaetes now called pogonophorans.  This recognizes the longer evolutionary history of protostomes.  It also sets aside changes made by the proposals of Lophotrochozoa and Ecdysozoa as significant groups of animals; the post of May 31, 2013 explains why they should be dismissed.

[Engemann's] Modification of the Annelid Theory of Chordate Origin

If you have read the recent posts of this blog, starting with SCIENCE PREJUDICE on March 17, 2016, you will understand why I didn’t say “The Creator’s Use of Annelids to Make Humans”.  My data driven conclusions leading to understanding of the evolutionary sequence of events involved do not discredit God by presenting it as a scientifically credible theory.  That is especially true because the multiple lines of evidence were unlikely to have been discovered by my feeble efforts.  I say the same thing about Darwin’s work on developing the Theory of Natural Selection underpinning our understanding of evolution.  I hope I will not withdraw recognition of the Creator’s role as Darwin may have done.  Maybe I should just say “Modified Annelid Theory of Chordate Origin”.

The lines of evidence

First, the observation of inverted systems, noted for annelids as compared to chordates, was responsible for the original proposal of annelid origin over a century ago.

Second, observations that evolution can occur in developmental stages independent of adult features.  This has been known for a long time without perception of its significance.

Third, evolutionary rates at the abyssal depths of the ocean can be so slow it makes molecular clocks for determining evolutionary rates in different branches of the tree of life almost meaningless.  Some evidence of it being known in 1915 exists*, but who would realize the importance of nothing happening?

Fourth, conditions in the abyssal depths were the driving force for natural selection to bring about the deuterostome embryological features from the original protostome annelid embryological features.

Fifth, the Pogonophora, unknown at the time of the original annelid theory, embed the major evidence of intermediate linking features.

Where is the evidence?

First, the inversion is illustrated in the post of March 2, 2015.  The concept was discussed in the June 28, 2013 post.

Second, this fact of some independent evolution of embryonic features is generally accepted since the “Biogenetic Law” was discredited.  I was impressed by the existence of an egg appendage (post of June 5, 2014) not found on more primitive isopods (post of June 6, 2014) illustrating the concept.

Third, factors responsible for the slow rate have accumulated but have not been linked with the remarkable longevity I have shown must exist, beginning with the evidence the pogonophorans present (Posted on October 24, 2015) discussed in the post of Jun 9, 2014 and illustrated in the post of June 13, 2014.

Fourth, a number of research reports have demonstrated the slowing of metabolic rates with depth in the ocean.  Some references are given in the post of June 22, 2013.  When data is limited some have assumed the ages of organisms fell at the lower end of the predicted range of error.  Isopod egg features noted in other posts apply to understanding the cleavage change (protostome to deuterostome type via pogonophorans) due to reduced egg membrane constriction as a possible selective force.

Fifth, the pogonophorans show a number of features intermediate between annelids and chordates noted in some of the posts referenced above and in the post of October 24, 2015.  Their importance is made clearer by their critical role in life surviving extinction events as discussed in my post on May 11, 2013.

The tree of life, revised

A simple correction for the tree of life is to leave the entire protostome line intact (from the version before the Lophotrochozoa/Ecdysozoa errors) and graft the deuterostome (or chordate) line on to the Pogonophora/Polychaeta basal group of the Annelida.  Echinoderms and perhaps some lophophorates may have ancestry among other pogonophorans than those leading to the chordate line.

*Brooks, William Keith.  1915.  The Foundations of Biology.  Columbia Univ. Press, New York.  339 pp.  He comments on - the unchanging nature of Lingula (page 219), and p. 217 “the diversity of the Lower Cambrian fauna and of its intimate relation to the fauna on the bottom of the modern ocean”.

Joseph G. Engemann   Kalamazoo, Michigan    May 1, 2016

THE MOON: ORIGIN, IMPACT ON US, AND DEMISE

WHY THE MOON?

Two days ago I was watching an episode of How the Universe Works, on the Science Channel.  Its original air date was 8/18/2015.  The title of the episode was "Secret History of the Moon".  There was a considerable amount of new information for me, especially the evidence of much more water, volcanic activity and resulting lava tubes that may possibly be used for establishing self sustaining colonies as a base of more distance space exploration.

It was somewhat oversold for its emphasis on possible dramatic explanations of its origin and ultimate demise taking us with it.  The end involves the expansion of the Sun billions of years from now.  Also, the hypothesis of a twin star of the Sun circling with us in a pattern that will provoke peaks of comets and meteors from the Oort Cloud beyond the known planets to endanger us with a cycle of recurrences every 20 some millions of years, is very speculative.  Such a periodic event would be much more regular than past extinction peaks indicate.

MOON ORIGIN

 It is reasonable that the moon's origin was part of the condensation of the early protoplanetary disk around the Sun and aggregation of particles.  The process would continue with greater efficiency, due to gravity increasing with mass, until the results were established in orbits around the sun as they are today.  Probably there were multiple small moons during an early phase, but the compactness of orbits close to the Sun made them more likely to collide and grow into the single moon the earth has.  The dozens of moons of Jupiter and Saturn and more distant planets shows moon accretion is probably a common process.

My contention that the asteroid belt between Jupiter and Mars seems consistent with the possible collision of two planets producing the fragments of the asteroid belt.  The fragments have been mostly swept from orbits of nearby planets - Jupiter, Mars, Earth and its moon.  This origin is consistent with the outer layers of moon and Earth having the same geology that has, probably erroneously, been considered evidence of the moon resulting from a collision with earth causing the similarity.

THE MOON'S IMPACT ON US AND EVOLUTION

I've heard or read that there is a peak of violent acts resulting in increased emergency room visits during the days around the Full Moon.  The word lunatic gets its origin from the phenomenon.  There is no bad magic about it, probably just an impact of poor sleeping with the greater night-time light.  But the approximate 28 days of the lunar cycle has probably selected the duration found in menstrual cycles.  The cycles of growth some marine mollusks show in their shells can reflect the lunar cycle.  They can also show the daily growth and seasonal growth so we know that near the beginning of the fossil record there were more days in a year before the tidal tug of moon on earth and/or a slowing due to space debris accretion made the days longer, but the year shorter in terms of number of days.

The craters on the moon seem better evidence of asteroid impacts than of volcanoes.  But the side facing us has the clearest evidence of volcanic activity.  The smaller size of the moon, compared to the earth, is consistent with an earlier cooling and lessening of volcanic activity.  The earth's greater size means it would collect more space debris (asteroids etc.) than the moon.  A Pre-Cambrian peak of that type of activity was probably a major selective force during extinction peaks shaping the pogonophoran link as noted in the post [ http://evolutioninsights.blogspot.com/2013/06/evolution_28.html ].

The post [ http://evolutioninsights.blogspot.com/2013/05/asteroid-strikes.html ] was my second post on this blog and enlarges on the comments of the evolutionary impact of asteroids and the deep sea as a refugium enabling the evolutionary events leading to the pogonophoran link of deuterostomes to protostomes.

If you think the collision of two planets causing the asteroid belt is improbable, check the graded spacing of planets and the gap between Mars and Jupiter.

Joseph G. Engemann  Kalamazoo, Michigan    January 7, 2016