DINOSAUR EXTINCTION

DINOSAUR EXTINCTION

A quick Google search confirmed my impression that the dinosaurs became extinct about 65,000,000 years ago at the end of the Cretaceous.  An exception was indicated by referring to the extinction as not including non-avian dinosaurs.  That distinction was made to satisfy scientists who have determined that bird’s ancestral reptilian roots was most likely in a specialized line of dinosaur-like ancestors.  It seems to me that it is unnecessary to continually repeat that connection in discussing non-phylogenetic issues.

Birds are sufficiently different from dinosaurs that they deserve their independency as a group.  Feather’s, no teeth, and homeothermy (maintaining a temperature independent of environmental temperature) may be avian characteristics that had a role in the survival of birds, but that is another topic.

THE MAJOR CAUSE, AN ASTEROID STRIKE

Multiple causes may have operated in making dinosaurs unable to survive the asteroid strike(s) that produced world-wide evidence of the disaster in the geological record found in sediments.  Several other major geological periods ended with similar disruptions, all also associated with the extinction of a large percentage of previously existing species.

In the several billion years of the earth’s existence earth has grown by the impact of space debris of varying sizes as indicated by the assortment of craters on the moon and other planets   Such bombardment was so intense in pre-Cambrian times that animals left a very skimpy fossil record, partially because large fossil forming animals seldom evolved or survived.

The abyss as a refuge during extinction events

The one place that had relatively stable conditions during extinction events was the abyssal region of the oceans.  There, any animals that could survive on the nutrients deposited in sediments had a better chance of survival in some location because most of the earth was covered with deep oceans.  The deep-water pogonophorans were one of the survivors.  The oxygenated region was so extensive and so slow to be replenished by polar surface waters that much of the fauna adapted to the region persisted to the present.  Those abyssal conditions made low metabolic rates and extended life cycles contribute to a very slow, almost absent, evolutionary rate for animals living there. (see 2015/05 listed at end of this post)

BEYOND THE ASTEROID IMPACT ZONE

Direct hits by the asteroid, its fragments, debris blasted from the impact zone did not even have to kill a single dinosaur.  But the world-wide atmospheric debris may have persisted for a year or more and made it difficult for significant plant growth of the type needed by large herbivores.  Carnivorous dinosaurs like T. rex would miss their normal food after large herbivores starved.  Continents isolated by oceans and partitioned by deserts or mountain rages would have made it difficult for the large dinosaurs to escape the drastic climatic shifts temporarily making their existing range uninhabitable.

POSSIBLE SECONDARY CAUSES OF DINOSAUR EXTINCTION

Pre-strike population declines or increases may have contributed to the death of many species.  Such declines may have been in the dinosaur species and/or other groups important in their food chains and are not limited to food organisms but could include microscopic disease organisms, parasites, and competitors of various types.  

The complexity of population changes resulting from decline or increase of one species is difficult to predict with certainty.  The decrease in one species may result in survival of more of those they prey upon and fewer of those feeding upon them. The changes can ripple up and down the food, predator, and parasite chains existing in the ecological community.  Add to these changes each of the physical changes produced by each species and the variability of possible community changes becomes astronomical.  If the vast number of buffalos grazing on our prairies had not been replaced by cattle, sheep, and farmers plowing- would much of it reverted to forest or scrubby vegetation providing homes for a different group of animals and plants?  Such changes had far reaching effects including soil erosion, flooding, less retention of water and less rainfall; all changes having additional effects on climate and life.

The cooling accompanying the atmospheric debris which reduced light energy and it warming effect makes a possible sufficient cause for extinction of many dinosaur species by shifting sex ratios of eggs hatching to all of one sex.  It is known that alligators and some other reptiles deposit large numbers of eggs in holes that they dig in the ground.  The holes are then covered over and the deeper the egg in the ground the cooler the temperature it experiences during embryonic development.  Higher temperatures induce one sex, cooler temperatures induce the other sex.  If cooler temperatures make all become the sex normally found in the deeper part of the nest, all will be of one sex.  It is not known if the phenomenon is the cause of alligators being restricted to warmer latitudes.

Cooler temperatures would make animals other than birds and mammals become inactive and unable to respond to egg predation or even being eaten by smaller animals with feather or fur insulation and higher metabolic rates maintaining body temperatures needed for activity.  The immense size of dinosaurs made them less susceptible to short term cold temperatures because it takes days for the largest to cool down, but the asteroid caused global cooling would persist so long it might have been sufficient to cause their demise, even those many other causes may have speeded the process of extinction.

Joseph Engemann     Kalamazoo, Michigan     October 20, 2016

http://evolutioninsights.blogspot.com/2014/03/science-extinctions-and-evolution.html

http://evolutioninsights.blogspot.com/2015/05/abyssal-ocean-environment-and-extreme.html 

EVOLUTION

Evolution and Asteroid Strikes

ASTEROID STRIKES HELPED SHAPE OUR EVOLUTION

Where would we be without asteroid strikes? 
                                   

We might still be here, but we would look entirely different.  Bombardment with asteroids and other space debris was much more common a billion years ago.  At that time life in our ancestral line had reached a worm-like stage that also gave rise to some other forms less like our egocentric selves.  The bombardment had an enormous impact on the course of evolution.

When God created the universe it began as a speck over twelve billion years ago as we measure time.  That speck was endowed with the properties that would spawn several generations of stars and the galaxies we see today.  It had all the potential for the formation of elements and star systems with associated planets as well as the evolution of life as we know it.  Darwin realized this as the work of the Creator before events sped his drift into agnosticism.

I know, from the things science has discovered, some major things that answer a few major evolutionary questions.  It is not because of personal brilliance or planning that I know them.  It is not because of some revelation that I know them.  It is the result of an unusual set of circumstances which I, have blundered into and, now view as God’s direction of the chance events that made it possible for me to put the bits of the puzzle together.

In 1987 two paleontologists (Raup and Sepkoski) published a study of extinction rates that showed high peaks associated with major asteroid impacts.  A regression line, which I calculated from their data, projected back over half a billion years to the beginning of the Cambrian where it reached a 100% extinction rate.  That obviously did not occur because there are Pre-Cambrian fossils, some of which had remains looking much like tubes of pogonophorans, which still live in the abyssal regions of the ocean bottom.

Pogonophorans were able to survive the Precambrian bombardment because they had evolved by natural selection to survive by absorbing nutrients from sediment and lost many of the typical annelid worm features of their ancestors.  They even lost the mouth and rigid early embryological features of their ancestral annelids.  Some changes now evident in their descendants led to, among other things- our systems being upside down as compared to most worms, our fertilized egg’s ability to have each of the early cells survive as twins or multiple births instead of dying when separated, and our pituitary to have its peculiar blend of hormones (the endodermal and ectodermal tissues that form the pituitary couldn't have joined if the pogonophoran pharyngeal region had not been suppressed during the period the former circumesophageal nerves were fusing).

Biologists think ancestral forms are replaced by new forms and cannot be found unchanged today.  But pogonophorans, because of the peculiar features of the deep sea have extremely long lives as individuals and thus those that stayed there evolved very slowly.

Many astronomers have come to believe the moon (Wikipedia, moon formation) started as a result of a collision of the earth with another heavenly body.  They believe the probability is very minuscule, but why bother when it is obvious that the following is much more likely.  The asteroid belt consists of orbiting fragments from a collision of two or more planets, or a planet and another major object, in that region between the orbits of Mars and Jupiter.  The scars on the moon, other planets, and large asteroids show the evidence of past impacts.  This immense accumulation of space debris was sufficient to slow the moon’s rotation so gravity’s effect could bring it to zero rotation with respect to the earth.  The earth’s greater mass was sufficient to keep it rotating even though we probably received more mass from space than did the moon, slowing us from 400 plus rotations per year to 365.  Tidal friction is used to explain the slowing of rotation for both the moon and the earth; but, shouldn't it have been more dramatically slowed for the earth with its oceans if that were true?

So we have cleaned out most of the fragments in earth’s orbital path and have a much reduced probability of an earth shattering strike from outer space than in prehistoric times.  The relative peace with the reduction or cessation of celestial bombardment, the last really major event being the strike that helped end the dinosaurs at the end of the Mesozoic about sixty-five million years ago, left a partial void that was repopulated in part by survivors from the deep sea.  The process of re-population from the deep-sea was much more important as the Cambrian began.

Incidentally, the idea of annelid worms being in our ancestral line was much more popular a hundred years ago.  Our annelid ancestry was rejected because of the great differences in embryology of annelids as compared to the vertebrates and invertebrates sharing our ancestral line starting with the pogonophorans.  When genetic information helped us see that the embryological differences were not the complete answer, the old annelid origin theory was not restored.  DNA/RNA studies are excellent for determining the relationships of closely related organisms.  Nucleic acid studies, as currently performed, have not yet been refined enough to project distant relationships. We know more about distant relationships from other data for widely different groups.

Almost anybody can write a book.  I've written a manuscript for one explaining some of the above.  But it runs counter to popular opinion of most students of evolution.  Why?  Probably because few biologists today have time for the range of course work common in my generation.  I had to dig into the literature on pogonophorans to revise an invertebrate zoology text for a second edition that was published in 1968.  I found that they must live for several thousand or more years, thanks, in part, to my knowledge of marine biology.  I might not have realized that if I hadn't developed an interest in causes of longevity during my doctoral studies (at MSU) comparing Michigan and Tasmanian isopod crustaceans (thanks to a 1956 Fulbright Grant for study at the University of Tasmania).

So the obscure pogonophorans that weren't even known about a hundred years ago provide important clues.  They show up in odd places in molecular studies of evolution because they have changed only slightly genetically while more recent groups have changed greatly.  Thus the great differences between the extremes of more recent groups are greater than the difference between either of the extremes and the pogonophorans.  I know it is due to the ancestral position of the pogonophorans and their extreme length of life.  My evolutionary colleagues think it can be explained away as an anomaly called “long-branch attraction”.

If my argument that major asteroid strikes are remarkably less likely in the future than in the past does not comfort you, consider the following.  If strikes are random, the likelihood of a strike is directly proportional to the area considered.  The mid-February one exploded above Chelyabinsk, Russia. On average, for every 63 that hit Russia, the largest country in the world, only 36 would hit the United States; about 100 would hit Russia while 1 is hitting Michigan; Liechtenstein would get about one strike for every 100,000 to hit Russia.  Kalamazoo is smaller than Liechtenstein, so sleep well tonight.  If you are still worried, remember that the one hitting Russia is only about the second big one to hit in the past one hundred and five years, the other knocked down trees over a large area in Siberia.

Oh, by the way, the regression line that I calculated hit 100% extinction rate at the beginning of the Cambrian, if I remember correctly, projecting forward, it did not hit zero anytime soon.  But with strikes in our area likely to be about once every twenty million years there doesn't seem to be much to worry about if the injuries are no worse than in Chelyabinsk.

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

This was written for, but not sent, to the Kalamazoo Gazette letters editor in late February. Edited 5/11/13.