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7.1E: The Fossil Record and the Evolution of the Modern Horse - Biology

7.1E: The Fossil Record and the Evolution of the Modern Horse - Biology



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LEARNING OBJECTIVES

  • Analyze the fossil record to understand the evolution of horses

Fossils provide evidence that organisms from the past are not the same as those found today, and demonstrate a progression of evolution. Scientists date and categorize fossils to determine when the organisms lived relative to each other. The resulting fossil record tells the story of the past and shows the evolution of forms over millions of years.

Case Study: Evolution of the Modern Horse

Highly detailed fossil records have been recovered for sequences in the evolution of modern horses. The fossil record of horses in North America is especially rich and contains transition fossils: fossils that show intermediate stages between earlier and later forms. The fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus Eohippus.

The first equid fossil was found in the gypsum quarries in Montmartre, Paris in the 1820s. The tooth was sent to the Paris Conservatory, where Georges Cuvier identified it as a browsing equine related to the tapir. His sketch of the entire animal matched later skeletons found at the site. During the H.M.S. Beagle survey expedition, Charles Darwin had remarkable success with fossil hunting in Patagonia. In 1833 in Santa Fe, Argentina, he was “filled with astonishment” when he found a horse’s tooth in the same stratum as fossils of giant armadillos and wondered if it might have been washed down from a later layer, but concluded this was “not very probable.” In 1836, the anatomist Richard Owen confirmed the tooth was from an extinct species, which he subsequently named Equus curvidens.

The original sequence of species believed to have evolved into the horse was based on fossils discovered in North America in the 1870s by paleontologist Othniel Charles Marsh. The sequence, from Eohippus to the modern horse (Equus), was popularized by Thomas Huxley and became one of the most widely known examples of a clear evolutionary progression. The sequence of transitional fossils was assembled by the American Museum of Natural History into an exhibit that emphasized the gradual, “straight-line” evolution of the horse.

Since then, as the number of equid fossils has increased, the actual evolutionary progression from Eohippus to Equus has been discovered to be much more complex and multibranched than was initially supposed. Detailed fossil information on the rate and distribution of new equid species has also revealed that the progression between species was not as smooth and consistent as was once believed.

Although some transitions were indeed gradual progressions, a number of others were relatively abrupt in geologic time, taking place over only a few million years. Both anagenesis, a gradual change in an entire population ‘s gene frequency, and cladogenesis, a population “splitting” into two distinct evolutionary branches, occurred, and many species coexisted with “ancestor” species at various times.

Adaptation for Grazing

The series of fossils tracks the change in anatomy resulting from a gradual drying trend that changed the landscape from a forested habitat to a prairie habitat. Early horse ancestors were originally specialized for tropical forests, while modern horses are now adapted to life on drier land. Successive fossils show the evolution of teeth shapes and foot and leg anatomy to a grazing habit with adaptations for escaping predators.

The horse belongs to the order Perissodactyla (odd-toed ungulates), the members of which all share hoofed feet and an odd number of toes on each foot, as well as mobile upper lips and a similar tooth structure. This means that horses share a common ancestry with tapirs and rhinoceroses. Later species showed gains in size, such as those of Hipparion, which existed from about 23 to 2 million years ago. The fossil record shows several adaptive radiations in the horse lineage, which is now much reduced to only one genus, Equus, with several species. Paleozoologists have been able to piece together a more complete outline of the modern horse’s evolutionary lineage than that of any other animal.

Key Points

  • A dog-like organism gave rise to the first horse ancestors 55-42 million years ago.
  • The fossil record shows modern horses moved from tropical forests to prairie habitats, developed teeth, and grew in size.
  • The first equid fossil was a tooth from the extinct species Equus curvidens found in Paris in the 1820s.
  • Thomas Huxley popularized the evolutionary sequence of horses, which became one of the most common examples of clear evolutionary progression.
  • Horse evolution was previously believed to be a linear progress, but after more fossils were discovered, it was determined the evolution of horses was more complex and multi-branched.
  • Horses have evolved from gradual change ( anagenesis ) as well as abrupt progression and division ( cladogenesis ).

Key Terms

  • cladogenesis: An evolutionary splitting event in which each branch and its smaller branches forms a clade.
  • equid: A member of the horse family.
  • anagenesis: Evolution of a new species through a large scale change in gene frequency so that the new species replaces the old, rather than branching to produce an additional species.

DNA sheds new light on horse evolution

Ancient DNA retrieved from extinct horse species from around the world has challenged one of the textbook examples of evolution -- the fossil record of the horse family Equidae over the past 55 million years.

The study, published in the Proceedings of the National Academy of Sciences, involved an international team of researchers and the Australian Centre for Ancient DNA (ACAD) based at the University of Adelaide.

Only the modern horse, zebras, wild asses and donkey survive today, but many other lineages have become extinct over the last 50,000 years.

ACAD Director Professor Alan Cooper says despite an excellent fossil record of the Equidae, there are still many gaps in our evolutionary knowledge. "Our results change both the basic picture of recent equid evolution, and ideas about the number and nature of extinct species."

The study used bones from caves to identify new horse species in Eurasia and South America, and reveal that the Cape zebra, an extinct giant species from South Africa, were simply large variants of the modern Plains zebra. The Cape zebra weighed up to 400 kilograms and stood up to 150 centimetres at the shoulder blades.

"The Plains zebra group once included the famous extinct quagga, so our results confirm that this group was highly variable in both coat colour and size."

Lead author of the paper, Dr Ludovic Orlando from the University of Lyon, says the group discovered a new species of the distinct, small hippidion horse in South America.

"Previous fossil records suggested this group was part of an ancient lineage from North America but the DNA showed these unusual forms were part of the modern radiation of equid species," Dr Orlando says.

A new species of ass was also detected on the Russian Plains and appears to be related to European fossils dating back more than 1.5 million years. Carbon dates on the bones reveal that this species was alive as recently as 50,000 years ago.

"Overall, the new genetic results suggest that we have under-estimated how much a single species can vary over time and space, and mistakenly assumed more diversity among extinct species of megafauna," Professor Cooper says.

"This has important implications for our understanding of human evolution, where a large number of species are currently recognised from a relatively fragmentary fossil record.

"It also implies that the loss of species diversity that occurred during the megafaunal extinctions at the end of the last Ice Age may not have been as extensive as previously thought.

In contrast, ancient DNA studies have revealed that the loss of genetic diversity in many surviving species appears to have been extremely severe," Professor Cooper says. "This has serious implications for biodiversity and the future impacts of climate change."

Story Source:

Materials provided by University of Adelaide. Note: Content may be edited for style and length.


7.1E: The Fossil Record and the Evolution of the Modern Horse - Biology

Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms. There are numerous examples of transitional forms in the fossil record, providing an abundance of evidence for change over time.

Pakicetus (below left), is described as an early ancestor to modern whales. Although pakicetids were land mammals, it is clear that they are related to whales and dolphins based on a number of specializations of the ear, relating to hearing. The skull shown here displays nostrils at the front of the skull.

A skull of the gray whale that roams the seas today (below right) has its nostrils placed at the top of its skull. It would appear from these two specimens that the position of the nostril has changed over time and thus we would expect to see intermediate forms.

But, the standard diagram does clearly show transitional stages whereby the four-toed foot of Hyracotherium, otherwise known as Eohippus, became the single-toed foot of Equus. Fossils show that the transitional forms predicted by evolution did indeed exist.


The Fossil Record

A homologous structure is a structure in organisms that shows that they used to be the same species a long time ago and have since diverged.

This can be seen in animals like humans and whales. Human hands and whale flippers have extremely similar bone structures. This leads scientists to believe that both species used to be one species.

Answer:

The idea that continental drift has taken place came up primarily because of study of fossils discovered from different corners of earth.

Explanation:

The word 'fossil' was coined more than 500 years ago, by German scientist Georgius Agricola, though records describing fossils are much older. It actually means 'having been dug up' in its original latin form.

In prechristian era, Greek philosophers discussed about fossils, later Leonardo da Vinci studied fossils in great detail so that he is today regarded as Father of Palaeontology. But it was Robert Hooke, author of Micrographia, who first realised that fossils are evidences of past life and more:

. if the finding of Coines, Medals, Urnes, and other Monuments of famous persons, or Towns, or Utensils, be admitted for unquestionable Proofs,that such Persons or things have, in former times had a being, certainly those Petrifactions may be allowed to be of equal Validity and Evidence, that there have formerly been such Vegetables or Animals. and are true universal Characters legible to all rational Men.

Before enlisting specific fossils which allow us to speculate the details of continental drift that has taken place on earth, let us see how the continents were arranged during mesozoic era .

()

Let us now focus on fossils which prove existence of Gondwanaland.

  • One type of fern, the Glossopteris , arose and flourished in southern hemisphere before becoming extinct in Permian.

Geologist Israel C White was the first person to report the similarities between coal (fossilised plants) found in Brazilian mines and that found in Africa. His insight helped Alfred Wegener to publish continental drift theory in 1912.

Fossils of reptile Lystrosaurus, which roamed the earth 250 million years ago: excavated and recovered from South Africa, India and Antarctica: therefore leaving no doubt that the three continental entities were once joined.

Another significant evidence comes in the form of Mesosaurus, reported from both South America and South Africa. The two continents are today separated by very vast Atlantic ocean.

()


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7.1E: The Fossil Record and the Evolution of the Modern Horse - Biology

The Fossil Record
Does Not Support Evolution But Is Positive Evidence For Creation!
Evolutionist-Converter Quotes from Video Lectures!

Professor Knockout Quotes!


The only official collection of quotes by Dr. Don Patton on the internet.

An important message from Dr. Patton regarding these quotes:
I use most of these quotes as handouts to provide documentation for my lecture series. They were not intended to stand alone as arguments by themselves. However this web site (www.bible.ca) convinced me that they could be useful as a reference tool, especially for those who attend the lectures, and I agreed. I commented at the time that some of the quotes would not make sense without the lecture. A few (two) have charged that a small number of these quotes misrepresent the intent of the context. When the charges were investigated, it was discovered, sure enough, if they had heard them used in the context of the lecture, they would have seen that the use was appropriate. It should be remembered that we are not quoting these individuals to imply that they are creationists. Rather, just the opposite. We are using them as antagonistic witnesses. When such individuals acknowledge facts contrary to their own interest, the credibility of their testimony increases dramatically. We want you to know that these individuals are devout evolutionists. It should also be remembered that the quotes are used as graphics in a lecture. It is easy to defeat the purpose of effective communication by too much detail in the graphic. A longer excerpt might be desirable but ineffective. This practical challenge is one of the reasons documentation is provided in the form of a handout, which allows one to check the entire book or article referenced. If you feel that any of the quotes are used in a "deceptive and misleading" way, please contact the webmaster a formal inquiry will be made of your concerns. We are not afraid to admit error and make changes.

Below is the outline for the video. We recommend you print the outline below before viewing the video. Then watch the video with the hard copy (printed) of the outline in your hand. Enjoy!  

Their Only Direct Evidence

S. M. Stanley , Johns Hopkins, "It is doubtful whether, in the absence of fossils, the idea of evolution would represent anything more than an outrageous hypothesis. . The fossil record and only the fossil record provides direct evidence of major sequential changes in the Earth's biota. " New Evolutionary Timetable , p.72, 1981

HISTORICAL - NOT EMPIRICAL , John H. Horner ". paleontology is a historical science, a science based on circumstantial evidence, after the fact. We can never reach hard and fast conclusions in our study of ancient plants and animals. These days it's easy to go through school for a good many years, sometimes even through college, without ever hearing that some sciences are historical or by nature inconclusive." Dinosaur Lives , 1997, p.19

Stephen J. Gould , Harvard, "The Cambrian Explosion occurred in a geological moment, and we have reason to think that all major anatomical designs may have made their evolutionary appearance at that time. . not only the phylum Chordata itself, but also all its major divisions, arose within the Cambrian Explosion. So much for chordate uniqueness. Contrary to Darwin's expectation that new data would reveal gradualistic continuity with slow and steady expansion, all major discoveries of the past century have only heightened the massiveness and geological abruptness of this formative event. " Nature , Vol.377, 26 10/95, p.682. "Since the so called Cambrian Explosion. no new Phyla of animals have entered the fossil record." Lecture at SMU, 10/2/1990

Richard Monastersky , Earth Science Ed., Science News, "The remarkably complex forms of animals we see today suddenly appeared. . This moment, right at the start of the Earth's Cambrian Period. marks the evolutionary explosion that filled the seas with the earth's first complex creatures. 'This is Genesis material,' gushed one researcher. . demonstrates that the large animal phyla of today were present already in the early Cambrian and that they were as distinct from each other as they are today. a menagerie of clam cousins, sponges, segmented worms, and other invertevrates that would seem vaguely familiar to any scuba diver." Discover , p.40, 4/93.

Richard Dawkins, Cambridge, "And we find many of them already in an advanced state of evolution, the very first time they appear. It is as though they were just planted there, without any evolutionary history. Needless to say, this appearance of sudden planting has delighted creationists. . the only alternative explanation of the sudden appearance of so many complex animal types in the Cambrian era is divine creation. ", The Blind Watchmaker , 1986, p229-230.

IN THE CAMBRIAN , John Repetski , U.S.Geol. Survey, "The oldest land plants now known are from the Early Cambrian. Approximately 60 Cambrian spore-genera are now on record. represent 6 different groups of vascular plants. " Evolution , V.13, 6/'59, p.264.. Daniel I. Axelrod , UCLA, "This report of fish material from Upper Cambrian rocks further extends the record of the vertebrates by approximately 40 million years." [WY, OK, WA, NV, ID, AR] Science , Vol.200, 5/1978, p.529.

TRILOBITE EYES ". trilobites may have been superior to current living animals. They had, in principle, perfect vision: They possessed the most sophisticated eye lenses ever produced by nature. . look like they were designed by a physicist." Science News , Vol.105, 2/2, 1974

"Trees" Contradicted By Fossils,

From Some Similarities, Ignoring Others

DISTINCT LIVING KINDS " Stephen J. Gould , Harvard, "Our modern phyla represent designs of great distinctness, yet our diverse world contains nothing in between sponges, corals, insects, snails, sea urchins, and fishes (to choose standard representatives of the most prominent phyla)." Natural History , p.15, Oct. 1990.

DISTINCT FOSSIL KINDS , . demonstrates that the large animal phyla of today were present already in the early Cambrian and that they were as distinct from each other as they are today. a menagerie of clam cousins, sponges, segmented worms, and other invertevrates that would seem vaguely familiar to any scuba diver." Discover , p.40, 4/93.

BLIND FAITH , Douglas Futuyma , "It is considered likely that all the animal phyla became distinct before or during the Cambrian, for they all appear fully formed, without intermediates connecting one form to another." Evolutionary Biology , 1985, p.325

"TREES" NOT FROM FOSSILS , Steven J. Gould , Harvard, "The evolutionary trees that adorn our textbooks have data only at the tips and nodes of their branches the rest is inference, however reasonable, not the evidence of the fossils.", Nat.His. , V.86, p.13.

ARRANGED, R.H. Dott , U.of Wis. & R.L.Batten , Columbia, AMNH, "We have arranged the groups in a traditional way with the 'simplest' forms first, and progressively more complex groups following. This particular arrangement is arbitrary and depends on what definition of 'complexity' you wish to choose. . things are alike because they are related, and the less they look alike, the further removed they are from their common ancestor." Evolution Of The Earth , p.602.

STORY TIME, Colin Patterson , Senior Paleontologist, British Museum of Nat. History, "I will lay it on the line--there is not one such fossil for which one could make a watertight argument." "It is easy enough to make up stories of how one form gave rise to another. But such stories are not part of science, for there is no way of putting them to the test. . I don't think we shall ever have any access to any form of tree which we can call factual." Harper's , Feb.1984, p.56.

similarity IS NoT genetic , Sir Gavin Debeer , Prof. Embry., U.London, Director BMNH, "It is now clear that the pride with which it was assumed that the inheritance of homologous structures from a common ancestor explained homology was misplaced for such inheritance cannot be ascribed to identity of genes. The attempt to find homologous genes has been given up as hopeless." Oxford Biology Reader , p.16, Homology an Unsolved Problem

R. H. Dott , Univ. of WI, R. L Batten , Columbia Univ., A.M.N.H., "Much research has been done in embryology since Haeckel's day, and we now know that there are all too many exceptions to this analogy, and that ontogeny does not reflect accurately the course of evolution." Evolution Of The Earth , p.86.

Simpson & Beck , "Haeckel misstated the evolutionary principle involved. It is now firmly established that ontogeny does not repeat phylogeny." Intro.To Biology, 1965,p.273.

Keith S. Thompson , Academy of Natural Sciences, "Surely the biogenetic law is as dead as a doornail. It was finally exorcised from biology textbooks in the fifties. As a topic of serious theoretical inquiry, it was extinct in the twenties." American Scientist , 5/6, 1988, p.273 " Ontogeny and Phylogeny Recapitulated "

Dr. Michael Richardson , St. George's Hospital Medical School, "What he did was to take a human embryo and copy it, pretending that the salamander and the pig and all the others looked the same at the same stage of development. They don't. . There's only one word for this, and Dr. Richardson doesn't flinch from using it. 'These are fakes. In the paper we call them misleading and inaccurate, but that is just polite scientific language." The Times (London), p.14, 8/11/97

" Fraud Rediscovered ", "In reality, Richardson and his colleagues note, even closely related embryos such as those of fish vary quite a bit in their appearance and developmental pathways. 'It looks like it's turning out to be one of the most famous fakes in biology.' . But Haeckel's confession got lost after his drawings were subsequently used in a 1901 book called Darwin and After Darwin and reproduced widely in English-language biology texts." Science , p.1435, V.277, 9/5/97

"Embryonic Fraud Lives On," "Although Hacckel confessed. and was convicted of fraud at the University of Jena, the drawings persist. 'That's the real mystery,' says Richardson." New Scientist , p.23, 9/6/97

New York Times , 4/8,/2001, "Several years ago, though, biologists discovered that many of the drawings were fraudulent. One of the texts that includes the faulty drawings is the third edition of "Molecular Biology of the Cell," the bedrock text of the field. Its authors include Dr. Bruce Alberts, a biochemist who is president of the National Academy of Sciences, and Dr. James D. Watson, the geneticist who shared a Nobel Prize for unraveling the structure of DNA."

UNRELATED SIMILARITIES , J.Z.Young, Professor of Anatomy, Oxford, ". similar features repeatedly appear in distinct lines. . so common that it is almost a rule that detailed study of any group produces a confused taxonomy. Investigators are unable to distinguish populations that are parallel. from those truly descended from each other." Life Of The Vertebrates, p.779 "From very different stocks, the marsupial carnivores and placental carnivores produced animals almost identical in physical form, the true wolf and the thylacine [marsupial wolf]. . their proportions are uncannily similar and their skulls are so similar that they are used as a classic 'spot the difference' examination question for zoology students." Prehistoric Life , p.187

"NOT SO HUMAN" "83% of the 231 genes compared had differences that affected the amino acid sequence of the protein they encoded. And 20% showed 'significant structural changes.' . we have seen a much higher percentage of change than people speculated."

SHEEPISH ANCESTORS? "Sue Galloway, of the University of Otago, who led the team that included scientists at Helsinki University in Finland, was quoted as saying, "Sheep are human, basically. Ninety-eight per cent of our genes are the same." Electronic Telegraph , 7/ 4/2000.

MICE & MEN "Overall, mice and humans share virtually the same set of genes. . On average, the protein-coding regions of the mouse and human genomes are 85 percent identical some genes are 99 percent identical" National Genome Research Inst., (9/2006)

Significant Change Is Not Observed

BOTHERSOM distresS , Stephen J. Gould , Harvard , "Every paleontologist knows that most species don't change. That's bothersome. brings terrible distress. . They may get a little bigger or bumpier but they remain the same species and that's not due to imperfection and gaps but stasis. And yet this remarkable stasis has generally been ignored as no data. If they don't change, its not evolution so you don't talk about it." Lecture at Hobart & William Smith College, 14/2/1980.

"We can tell tales of improvement for some groups, but in honest moments we must admit that the history of complex life is more a story of multifarious variation about a set of basic designs than a saga of accumulating excellence. . I regard the failure to find a clear 'vector of progress' in life's history as the most puzzling fact of the fossil record. . we have sought to impose a pattern that we hoped to find on a world that does not really display it." Natural History , 2/82, p.2

Required Transitional Forms Missing

DARWIN'S BIGGEST PROBLEM , ". innumerable transitional forms must have existed but why do we not find them embedded in countless numbers in the crust of the earth? . why is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain, and this perhaps is the greatest objection which can be urged against my theory". Origin Of The Species, Facsimile of First Edition, 1964, p.172

BIGGER NOW , David M. Raup, U. Chicago C., "The evidence we find in the geologic record is not nearly as compatible with darwinian natural selection as we would like it to be. Darwin was completely aware of this. He was embarrassed by the fossil record because it didn't look the way he predicted it would. Well, we are now about 120 years after Darwin and the knowledge of the fossil record has been greatly expanded. We now have a quarter of a million fossil species but the situation hasn't changed much. . ironically, we have even fewer examples of evolutionary transition than we had in Darwin's time. By this I mean some of the classic cases of Darwinian change in the fossil record, such as the evolution of the horse in North America, have had to be discarded or modified as the result of more detailed information." F.M.O.N.H.B., V.50, p.35.

PREDICTION FAILED , Niles Eldridge, American Museum Of Natural History "He prophesied that future generations of paleontologists would fill in these gaps by diligent search. . it has become abundantly clear that the fossil record will not confirm this part of Darwin's predictions. Nor is the problem a miserably poor record. The fossil record simply shows that this prediction was wrong." The Myths of Human Evolution, p.45-46

TEXT BOOK DECEIT, George G. Simpson , "The uniform, continuous transformation of Hyracotherium into Equus, so dear to the hearts of generations of textbook writers never happened in nature." Life Of The Past , p.119.

Colin Patterson , Senior Paleontologist British Museum of Natural History, "There have been an awful lot of stories, some more imaginative than others, about what the nature of that history [of life] really is. The most famous example, still on exhibit downstairs, is the exhibit on horse evolution prepared perhaps fifty years ago. That has been presented as the literal truth in textbook after textbook. Now I think that that is lamentable, particularly when the people who propose those kinds of stories may themselves be aware of the speculative nature of some of that stuff." Harper's , p. 60, 1984.

Derek Ager , U.at Swansea, Wales, "It must be significant that nearly all the evolutionary stories I learned as a student. have now been 'debunked.' Similarly, my own experience of more than twenty years looking for evolutionary lineages among the Mesozoic Brachiopoda has proved them equally elusive." Proceedings of Geological Association. , Vol.87, p.132

BIRD TEETH , Martin, Stewart , Whetstone Museum Of Natural History, U. Of Kansas, "Therapod dinosaurs, by comparison, have serrated teeth with straight roots and no constriction. . Archaeopteryx has unserrated teeth with constricted bases and expanded roots like those of other Mesozoic birds."" The Auk , V.97, p86, 1980.

"BIRD-BRAINED" "Researchers at the U. of Texas, Austin have used a computerized x-ray technique to build a three dimensional picture of the inside of the skull and inner ear of a fossil archaeopteryx. From this they deduced Archaeopteryx had a brain and inner ear very similar to living birds. well suited for flight." Science Now , 8/4/2004

FOSSIL BIRD EARLIER , "Fossil remains claimed to be of two crow-sized birds 75 million years older than Archaeopteryx have been found. a paleontologist at Texas Tech University, who found the fossils, says they have advanced avian features. . tends to confirm what many paleontologists have long suspected, that Archaeopteryx is not on the direct line to modern birds." Nature , Vol.322, 1986 p.677.

BIRDS FROM DINOSAURS? Douglas Futuyama , University Of NC "Yale University released. a landmark publication. 'the impetus for the book was the fact that this dinosaurian origin of birds had become, overnight, the dogma in the field, and many of us from the ornithological side felt that was simply wrong . that birds descended from dinosaurs is utter nonsense." Chronicle Of Higher Education , 10/25/96.

REPTILE TO BIRD , W.E. Swinton , "The origin of birds is largely a matter of deduction. There is no fossil evidence of the stages through which the remarkable change from reptile to bird was achieved." Biology & Comparative Physiology Of Birds , Vol.1, p.1.

D.B. Kitts , U.of OK, "Despite the bright promise that paleontology provides a means of "seeing" evolution, it has presented some nasty difficulties for evolutionists, the most notorious of which is the presence of 'gaps' in the fossil record. Evolution requires intermediate forms between species and paleontology does not provide them. The 'fact that discontinuities are almost always and systematically present at the origin of really big categories' is an item of genuinely historical knowledge." Evolution , Vol.28, p.467.

D.S. Woodroff, U.of CA, San Diego, "But fossil species remain unchanged throughout most of their history and the record fails to contain a single example of a significant transition." Science , Vol.208, 1980, p.716.

Stephen M. Stanley , Johns Hopkins U., "In fact, the fossil record does not convincingly document a single transition from one species to another." The New Evolutionary Timetable , 1981, p.95. David W. Swift , University Of Hawaii, ". no phylum can be traced from a preceding one in the fossil record, in fact we cannot account for the origin of a single phylum: they all appear abruptly. This is also true of lower taxonomic groups such as classes and orders, and possibly lower still." Evolution Under The Microscope , 2002, p.295

A MATTER OF FAITH , A.C. Seward , Cambridge, "The theoretically primitive type eludes our grasp our faith postulates its existence but the type fails to materialize." Plant Life Through The Ages , p.561.

BLIND FAITH, Niles Eldredge , Columbia U., American Museum Of Natural History, "And it has been the paleontologist- my own breed-who have been most responsible for letting ideas dominate reality: . We paleontologist have said that the history of life supports that interpretation [gradual adaptive change], all the while knowing that it does not." Time Frames , 1986, p.144

Unobserved imagined scenario to explain missing evidence,

based on fossils not found and a mechanisms not observed

Gould & Eldredge , "In fact, most published commentary on punctuated equilibria has been favorable. We are especially pleased that several paleontologists now state with pride and biological confidence a conclusion that had previously been simply embarrassing 'all these years of work and I haven't found any evolution'. (R.A. Reyment) Paleobiology , Vol.3, p.136.

S. M. Stanley , Johns Hopkins "The record now reveals that species typically survive for a hundred thousand generations, or even a million or more, without evolving very much. We seem forced to conclude that most evolution takes place rapidly. a punctuational model of evolution. operated by a natural mechanism whose major effects are wrought exactly where we are least able to study them - in small, localized, transitory populations. The point here is that if the transition was typically rapid and the population small and localized, fossil evidence of the event would never be found." p.77, 110, New Evolutionary Timetable, 1981.

Colin Patterson , B.M.N.H. "Well, it seems to me that they have accepted that the fossil record doesn't give them the support they would value so they searched around to find another model and found one. . When you haven't got the evidence, you make up a story that will fit the lack of evidence." Darwin's Enigma , p.100

Implication Of The Fossils

PALEONTOLOGY DOES NOT PROVE , D.B. Kitts , U.of OK, "The claim is made that paleontology provides a direct way to get at the major events of organic history and that, furthermore, it provides a means of testing evolutionary theories. . the paleontologist can provide knowledge that cannot be provided by biological principles alone. But he cannot provide us with evolution." Evolution , Vol.28, p.466

DON'T USE THE FOSSILS , Mark Ridley, Oxford , ". a lot of people just do not know what evidence the theory of evolution stands upon. They think that the main evidence is the gradual descent of one species from another in the fossil record. . In any case, no real evolutionist, whether gradualist or punctuationist, uses the fossil record as evidence in favour of the theory of evolution as opposed to special creation." New Scientist , June, 1981, p.831.


Evolution Of The Horse Worksheet Answers

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7.1E: The Fossil Record and the Evolution of the Modern Horse - Biology

Paleontology catalogs appearance & disappearance of 'types' in geological timescale
Origins of major taxa correspond to evolution of distinct types of organisms
REMEMBER that new taxa are recognized retrospectively
Lineages may not go extinct, even though forms change
What sorts of evolutionary phenomena are apparent in the fossil record?

Evolutionary Trends : patterns of change within taxa that persist over time
Trends may be observed across many taxa => 'rules' (cf. ecogeographic rules)
Cope's Rule : descendant species are larger than ancestral species
Ex.: >10X increase from Eocene Hyracotherium to Recent Equus
Williston's Rule : serial homologues become specialized & reduced in number
Head, thorax, & abdomen of Insecta from segmented ancestors
Trends can be quantified

Adaptive Radiations : proliferation of taxa after morphological innovation or entry into new niche
Ex.: Placodermi were first gnathostomes (opposable jaw elements)
Six orders evolve in Devonian: first vertebrate predators
Eutheria [placental mammals] at K / T boundary ( Cretaceous / Tertiary , 65 MYBP)
Mammalia are small noctural insectivores for first 120 Myr [see Eomaia at 125 MYBP]
Extinction of dinosaurs opens aquatic & aerial niches
From late Cretaceous Paleocene early Eocene ( = 20 Myr)
>20 new orders: including bats & whales

Living Fossils : persistance of taxa unchanged with low diversity over long periods
Mosaic evolution : different features evolve at different rates
'Fossils' are not necessarily primitive
'Living Fossils' do not necessarily represent ancestral type
Tadpole shrimp (Triops: Notostraca)
Fossils from 180 MYBP assigned to extant species
Coelacanth (Latimeria: Crossopterygia) survives from Carboniferous (250 MYBP)
Re-discovered in 1938 in Indian Ocean
Fin structure resembles immediate ancestors of terrestrial vertebrates,
Extinct crossopterygia are freshwater: marine habit is derived
Tuatara (Sphenodon: Rhynchocephalia) confined to islands off New Zealand
Parietal 'third eye', diapsid temporal openings in skull are ancestral
[Poor taxonomy may have led to extinction of other species]

Taxon cycles : Taxa originate, proliferate, 'rusticate'
Lungfish (Dipnoi: Sarcopterygia ) are first terrestrial vertebrates
High diversity in Paleozoic (20 genera),
Low diversity in Cenozoic (3 species in 3 Gondwanaland continents)
[But: fleshy-limbed, air-breathing relatives attend university]
Horses (Equidae: Perrisodactyla ) evolved in the New World
Originate in Paleocene as digitigrade 3-toed browsers (65 MYBP)
Proliferate in Miocene grasslands as cursorial 3-toed grazers (20 MYBP)
Replaced in Plio-Pleistocene by Artiodactyla (5 MYBP)
Artiodactyla have more efficient digestion & locomotion
Extant Equus survives only in Old World as cursorial 1-toed grazer

Missing Links : expected fossils that show transitions between groups are absent
Historically: applied to fossil intermediates between apes & humans
Neanderthals were first hominid fossils (1856):
now Homo sapiens neanderthalensis
"Piltdown Man" had cranium of modern human, jaw of ape
A hoax: two modern, artificially aged skulls combined
"Nebraska Man" identified from fossil molar teeth:
Tentatively identified as New World hominid (unlikely)
Subsequently shown to be an extinct pig
Ramapithecus argued to be a hominid at 15 MYBP
human / ape split very old
Now recoginzed as extinct pongid: human split

4 MYBP
Australopithecus has intermediate size, stance, skull
"Lucy" is oldest human ancestor (3.5 MYBP)
[but see Kenyanthropus, "Nature," 22 Mar 2001]

Homo floresiensis : the original "hobbit" ?
1-m tall hominin with small encephalization quotient
A H. erectus descendant contemporary with H. sapiens at 18KYBP ?

Major adaptive types appear 'suddenly'
First bird (Archaeopteryx) flies, has fully-formed feathers
First bat (Icaronycteris) is fully-formed Microchiropteran (w/ long tail)
moth scales in gut region echolocation
First whales (Archaeocetes) are fully aquatic
Origins & relationships of invertebrate taxa are notoriously poor

Mass Extinctions : 'Catastrophism' revisited
End of Paleozoic & Mesozoic Eras characterized by major extinctions

" Great Permian Die-off " (250 MYBP): Extinction of marine invertebrates
> 50% of families, > 95% of species
marine vertebrates, terrestrial life unaffected
" Cretaceous (K/T) Extinction ": Extinction of Dinosauria
All vertebrates > 25 kg gone plankton & benthic invertebrates gone
Marine fish & terrestrial plants unaffected
" Asteroid Holocaust " Theory
" Iridium Anomaly " at K / T Boundary (Alvarez 1980)
"Nuclear Winter" scenario predicts mass extinction
Impact seems certain: biological effects uncertain
26 MY extinction cycle may be related to extraterrestrial impacts
" Pleistocene Extinction " (10,000 BP)
Disapperance of New World megafauna (large mammals & birds)
ground sloths, mammoths, sabre cats, Diatryma, etc.
Coincides with arrival of first humans: the "Overkill" Hypothesis

" After Man " (Dougal Dixon)
What will Life be like 50 MYr after the extinction of Homo?
Premise: "ecological disaster" wipes out all large mammals
survivors are small, r-selected, nocturnal
Rabbucks are deer-like rabbits
Falanx are predatory, cursorial rats
Night Stalkers are flightless bats

Gradualist versus Punctuationalist Interpretations of the fossil record

Modern Synthesis : Evolution is 'slow and gradual'
Microevolution is the result of Natural Selection:
(differential survival & reproduction of individuals)
New variation arises from two main sources:
Mutation produces new alleles
Genetic recombination produces new allelic combinations

Macroevolutionary patterns result from microevolutionary processes,
continued over vast periods of time: " Gradualism "

'Evolutionary Trends' are due to directional selection
acting persistently & consistently over millions of years
Ex.: Hypsodont molars of horses evolve at 40mD s = 10 -6
1 death / 10 6 individuals / generation for 16 MYR
Ex.: Cranial capacity of Homo 850cc 1330cc in 1 Myr
increase of

Natural Selection with selection coefficients so small as to be immeasureable
can produce major evolutionary change in long term

'Adaptive radiations' are due to diversifying selection:
Evolutionary innovation allows entry into new niche

'Living fossils' are due to stabilizing selection:
Successful lineages become specialized

The Origin of Species
Speciation occurs mainly by adaptive divergence
Differences among species accumulate by microevolution.
This results in phyletic evolution :
species gradually change into new species
Ex.: Evolution of proloculus size in Lepidolina (Foraminifera) during Permian

Speciation is not adaptive per se:
i.e., creation of new species does not create selective advantage
RIMs arise by chance while population are isolated
SRMsevolve within populations by adaptation during divergence
anagenesis produces cladogenesis

The fossil record is very incomplete
Very few organisms leaves fossils
Ex.: Oceanic & tropical species unlikely to fossilize
'species gaps' are only apparent, not real
A more complete record would show infinite gradation
Ex.: Evolution of molars in Pelycodus (Primata: Mammalia) during Eocene
Notharctus arises from Pelycodus gradually
'missing links' are rare & temporary not seen

Microevolution explains macroevolution: end of story (& the course)


The Punctuated Equilibrium Model (Eldredge & Gould 1972)
A challenge to conventional interpretations

HYPOTHESIS :
The fossil record is complete
'species gaps' are real:
Intermediates don't exist
Rapid 'founder effect' speciation is the rule
Speciation is geologically instantaneous [< 50K years] => no fossils

Cladogenesis produces anagenesis
Species' genotypes are too stable: phyletic evolution is rare
A (tricky) population genetic argument (Lande 1983):
Recall: 40mD horse molar evolution implies s = 10 -6
Because genetic drift > selection if Ne

1/s
A "gradual" trend requires N e > 1,000,000 over 16 MYr
But: observed horse N e < 10

50,000
genetic drift would swamp such a weak selection coefficient
Thus, if horse evolution is the result of natural selection
s must have been quite high (s > 10 -4

5 )
and evolution would have occurred quite "quickly": 10s

Horse evolution can be explained by brief periods of rapid change
interspersed among longer period of little or no change.

Important : a "geologically instantaneous" interval of 50,000 yr
comprises many, many generations

Evolution proceeds as a punctuated equilibrium :
New species are produced by 'founder effect' speciation:
'Genetic revolutions' & selection for SRMs leads to a rapid 'adaptive shift'

Extant lineages are replaced by their descendants:
Geological picture is an extant lineage "suddenly" replaced by new lineage
[i.e., an anagenetic 'equilibrium', 'punctuated' by cladogenetic speciation]

Ex.: Lake Turkana snails show punctuated events correlated with changes in water level
Ex.: Re-interpretation of Pelycodus fossil record shows
episodes of rapid change & reversal (statistical artefacts?)
origins of new taxa might arguably be "instantaneous"

So which is correct ? Balance of supporting evidence is not clear
Paleontological "connect the dots" on same data can support
"gradual", "punctuated", or "mixed" models (See Fig. 6-12)

Iconography of evolution is changing in textbooks
"gradual" diagrams are being replaced by "punctuated" diagrams
Ex.: Horse evolution is one of the best studied examples
Historically, evolution is shown as a linear progression
Modern Synthesis diagrams are "slanted" " slow & gradual "
Post-Modern texts show "rectangular" phylogeny diagrams " punctuated "
[See also Campbell (1999)]


Can Macroevolution & Microevolution be 'decoupled'?

Microevolution by natural selection works through
differential survival & reproduction of individuals:

Evolutionary trends may be due to species selection =
differential 'survival & reproduction' of evolutionary lineages
'survival' = persistence (avoidance of extinction)
'reproduction' = production of new lineages (speciation)
Might different biological properties be selected at individual & species levels?

Differential extinction: The evolution of sex
Asexual propagation may be favored in short term
Uniform clone may be favored by stabilizing selection
But: any single clone is subject to extinction
Sexual reproduction may be favored in long term
Recombinant variants are eliminated by selection
But: multiple new adaptive types may survive extinction
Ex.: Daphnia populations (research of D. Innes )
asexual reproduction favored in stable environemtns
sexual reproduction favored in variable environments
An ecological disaster might destroy a plentiful, uniform asexual clone,
while an uncommon, diverse sexual clade would survive

Differential speciation: The evolution of dispersal strategies
'Stay at home' may be safer strategy in short term
chances of survival better in known environment
But: survival is poor during high density
'Dispersal' may be favored in long term
most colonies fail (recall 'founder' model)
But: some succeed as new species
Ex.: Rodents undergo population cycles
Lemmings (Microtus) are territorial at low density,
become 'migratory' at high density
Migratory individuals may found successful new colonies

Speciation per se is an adaptive strategy:
Lineages that disperse more persist longer
because dispersion leads to speciation
Rodents are extremely speciose (about 1/4 of mammalian diversity)

Macroevolution may require a new set of evolutionary explanations
a complete theory of evolution will consider extinction & speciation patterns