Les crapaudines,
qui sont des dents de poissons, proviendraient de la tête de crapauds et
auraient des pouvoirs de guérisons au Moyen Age. Les concoctions de ces
pierres de crapauds étaient censées protéger de la peste. Mais extraire
ces pierres des crapauds était tout un art: ce dernier devait être
vivant, placé sur un linge rouge et pendant qu'il était distrait, la
pierre tombait de sa tête. On en retrouve dans la joaillerie comme
contre poison esthétique.
A Malte ces
dents étaient connues sous le nom d'yeux de serpents. Le lien est à
faire avec St Paul: on dit que les serpents maudits par l'apôtre
perdirent leurs yeux, qui furent incorporés dans les rochers de l'île.
Les bélemnites
tomberaient comme la foudre durant les
orages.En Chine, ils étaient réputés guérir certaines maladies tout
comme les brachiopodes.
En raison de leurs formes aiguës, on l'a par le passé cru que des
bélemnites ont été moulés pendant les orages. Ceci a provoqué leur nom
largement répandu, coups de foudre. Dans quelques régions de
l'Angleterre des bélemnites sont connus comme doigts du diable ou doigts
de Saint Peter. Les Bélemnites par le passé étaient censés avoir des
qualités médicinales et ont été employés en tant que traitements pour le
rhumatisme et les yeux endoloris chez l'homme et les chevaux. Ils ont
été également employés pour protéger de la foudre et des démons du ciel.
En Ecosse, la
mention la plus vieille des bélemnites date de c1703 où ils sont désigné
sous le nom des botstones. Ils ont été employés par quelques Ecossais
pour traiter les chevaux des vers - le remède était l'eau qui avait été
trempée dans les bélemnites. En Chine les bélemnites sont connues comme
pierres d'épée. Le folklore scandinave considère des bélemnites comme
des bougies appartenant aux elfes, aux gnomes et aux lutins.
En Russie des
bélemnites avec des perforations fines ont été trouvés dans un
emplacement archéologique de 20.000 ans connu sous le nom de Kostenki.
Tours initiaux périsphinctoïdes,
fortement costulés ; tours externes bituberculés, épineux ou avec des
cotes simples, grossières ; microconques de petite taille, à costulation
non tuberculée et un péristome portant des apophyses ; macroconques de
grande taille, ornés successivement de côtes similaires à celles des
microconques puis de deux rangées de tubercules, l'une latéro-ombilicale,
l'autre latéro-ventrale, avec un péristome simple ; absence de
constrictions, de sillon ventral dans les premiers stades costulés et de
formations paraboliques dans les premiers stades de développement ;
ligne de suture assez simplifiée, à lobe latéral constamment plus long
que le lobe ventral et lobe suspensif légèrement décurrent constitué de
deux, voire trois, lobes auxiliaires réduits. Jurassique moyen (Callovien supérieur) - Jurassique supérieur (Oxfordien
supérieur
Les fossiles, en tant qu'éléments
matériels, sont connus de l'Homme depuis des âges très anciens.
Aristote, par
exemple, fait référence à des éléments fossilisés. Toutefois, les deux
idées essentielles à leur propos, i.e. leur origine
organique
et le fait qu'il s'agit de témoignages que d'autres formes de vie aient
existé avant l'Homme, n'ont pas été véritablement appréhendées avant le
XVIIe
siècle.
Les
premiers progrès réels découlent d'une proposition explicitée au début
du
XVIIIe
siècle : les terrains contenant des fossiles d'animaux ou végétaux
marins devaient en toute logique avoir été recouverts par la mer, afin
qu'ils s'y déposent sur le fond et s'enfoncent sur le lit
sédimentaire.
C'est la première fois que le fossile est envisagé comme indice
stratigraphique.
Toutefois, le poids intellectuel de l'idée de
génération spontanée,
selon laquelle les espèces étaient apparues les unes après les autres et
d'origine divine, empêcha une interprétation systématisée et approfondie
des causes du renouvellement des espèces, tel que logiquement déduit de
l'étude des fossiles.
À la suite de ces premiers progrès,
l'idée d'une filiation entre les espèces fait son chemin, notamment par
les écrits de
Geoffroy Saint-Hilaire
et
Lamarck.
S'opposent alors les visions
créationniste,
fixiste d'une
part,
transformiste,
évolutionniste
d'autre part. Le cœur de la controverse est atteint lorsqu'à la question
des origines de la vie animale et végétale est mêlée celle des origines
de l'Homme.
C'est également au
XVIIIe
siècle que trois grandes branches scindent la
paléontologie —
et subsistent encore à ce jour, sous la forme de spécialités
disciplinaires : la paléontologie descriptive et comparative, de
Cuvier ; la
paléontologie évolutive, de
Lamarck ; un peu
plus tard, la paléontologie stratigraphique, d'Oppel
et d'Orbigny.
Suit la
paléogéographie
vers 1830.
De façon très nette, paléontologie et
fossile se sont opposés de facto à une
Église
dogmatique, de la
même manière que l'astronomie
au
Moyen Âge.
Multidisciplinaire, organisée comme une enquête historique, l'étude des
fossiles a également eu des implications importantes sur le rapport de
l'Homme au
temps, par
exemple sur la question de l'âge de la Terre ou du vivant, ou encore sur
la question des durées — l'unité temporelle de base d'un fossile est le
million d'années,
un laps de temps difficilement imaginable. Grâce à des progrès rapides
et importants dans les techniques d'observation et d'investigation, la
connaissance des fossiles et de la fossilisation au cours des
temps géologiques
a réalisé ses plus grandes avancées à partir du
XIXe siècle.
Le dernier fossile à avoir été
découvert est celui du
Lognkosauria,
fossile découvert en 2007, son squelette était à 70% et est le 3e plus
grand jamais découvert dans le monde et aussi le plus complet d'entre
eux.
Le but de ce site est de présenter le
plus grand nombre possible de photos de coquilles fossiles (gastropodes
et bivalves) du tertiaire, afin de permettre à chacun de découvrir la
diversité et la beauté de ces fossiles.
Un autre but est de faciliter l´identification par des amateurs. Pour
cela, les photos sont organisées en base de données. Chaque photo
possède une notice comportant de nombreuses informations, dont les
renseignements taxonomiques tirés de la base de données de référence du
Museum d´Histoire Naturelle,
la localisation, la taille... Soyez toutefois bien conscients des
limites de l'identification sur photo, qui ne remplace ni l'exemplaire
en main ni la lecture des diagnoses. En cas de doute sur
l'identification d'un specimen, vous pouvez vous inscrire sur le forum
Coquillages actuels et fossiles
et demander de l'aide dans la rubrique
Identifications
Ambre de Colombie : En lithothérapie,
cette résine fossile âgée de 500 000 ans est associée au réchauffement
du corps au métabolisme cellulaire et au système immunitaire
Spécialiste dans l'énergie des minéraux pour les
soins et la méditation. Un catalogue de 550 minéraux avec leur
application, leur photo et le tarif : pierres brutes, polies et de
collection. Boules, oeufs, objets et colliers. Vente de fossile
Los fósiles son vestigios en sustrato
pétreo de antiguas criaturas vivientes de diferentes tipos (tanto
vegetales como animales), y que pueden encontrarse en los estratos
geológicos de la superficie terrestre.
Los fósiles más reconocibles por
el público son los restos petrificados de esqueletos o caparazones de
criaturas, sin embargo los restos fósiles no se limitan a las partes
duras petrificadas de dichas criaturas; se consideran también como
fósiles: los restos sin alterar, las impresiones, vestigios o moldes que
dejan en diferentes sustratos geológicos, las diferentes partes
anatómicas de organismos que no son de la época
présente
El Doctor Michael Benton es un paleontólogo de vertebrados con un
interés particular en los orígenes de los dinosaurios y en la historia
de los fósiles. Actualmente estudia a ciertos dinosaurios basales
provenientes del Triásico Bajo y la calidad de los diferentes segmentos
del registro fósil. Él es Director de Paleontología de Vertebrados en la
Universidad de Bristol, en el Reino Unido, además de dirigir el programa
de maestría en paleobiología en esa universidad. Él ha escrito más de 30
libros sobre dinosaurios y paleobiología, desde tomos profesionales
hasta libros populares para niños.
Todos los elementos radiactivos tienen vidas medias diferentes. El C14,
por ejemplo, tiene una vida media de 5,700 años. El uranio 235, por su
parte, tiene una vida media de 700 millones de años. "Es asombroso, pero
gracias al uso de este método científico podemos decir cuán antiguo un
elemento es si sabemos cuánto del elemento está en forma radiactiva y
cuánta descomposición hacia su estado original un elemento ha sufrido.
Durante su estado regresivo (estado regresivo hacia su estado original),
un elemento puede pasar por estados diferentes."
El
sistema de medición del Carbono 14 está basado en la misma metodología
usada para determinar los datos arrojados con la analogía de la vela.
Los científicos "creacionistas" ASUMEN también que la cantidad de C14 en
la atmósfera se ha mantenido constante a través del tiempo. EN CIENCIA,
como el ejemplo de la vela mostró, ESO ARROJA PROPOCIONES Y
ESPECULACIONES, NUNCA RESULTADOS DE ORIGEN INDISCUTIBLES!
En
conclusión…
Los métodos radiometrito usados para obtener la fecha de la existencia
de la tierra y lo contenido en ella envuelve SUPOSICIONES que no pueden
ser probadas. Como declaramos anteriormente, NO EXISTE UN SÓLO MÉTODO DE
DATACIÓN CIENTÍFICA que pueda ser usado para determinar la edad de los
fósiles y las rocas sedimentarias con absoluta cercioridad. De los
numerosos métodos para calcular la edad de la tierra, el sistema solar,
y el universo, los evolucionistas descartan todos las EVIDENCIAS que les
dicen que el Universo es joven, y entonces usan solamente los métodos
que tienden a apoyar su creencia (su fe) en la Teoría de la Evolución.
Alethopteris
é un parataxón, un xénero-forma. Os paleontólogos empregan este
termo para referirse a un determinado tipo de fronde, no que as pínulas
das frondes son adnatas e linear-lanceoladas
Os únicos restos fósiles
dos condrictios adoitan se-los seus dentes. Os dentes de Carcharodon
son triangulares e anchos cun suave escote na súa raíz. O escote e a
forma do dente son as razóns para que ata o século XVIII, a xente crera
que eran linguas petrificadas de serpe (as glosopétreas),
atribuíndoles propiedades protectoras contra os velenos, en particular
os das cobras. Para Plinio o Vello, as glosopétreas caían do ceo durante
as eclipses de Lúa.
Annularia é o nome das follas de Calamites. Están dispostas
en verticilos con 8-13 fojas cadanseu. A súa forma é variable: oval en
A. sphenophylloides ou máis ou menos linear-lanceoladas en
A. radiata.
Quand un fossile est recouvert par des
sédiments, il subit des changements de pression et de température, ainsi
que la circulation des fluides. Si ces fluides ont une composition
chimique proche de celle du fossile, ça n'aura pas beaucoup d'incidence.
Dans le cas contraire, la différence de composition peut entraîner des
modifications. Par exemple : une coquille carbonatée tombe dans des
argiles (qui deviendront des schistes par la suite). Si nous avons
circulation de fluides acides, le CaCO3 de la coquille va être dissout.
Ceci a par pour conséquence la perte de la structure interne, nous
n'avons plus de 'fossile corporel', mais un moule interne et un externe
Les fossiles ont été depuis tout
temps sujet d'admiration et de questionnement pour l'Homme. Avant
l'avènement de la Paléontologie, de nombreuses croyances existaient à
leur égard. Cette page recense quelques uns de ses mythes
La Formation de Mingan tire son nom de
l’archipel de Mingan tandis que la Formation de Romaine a été nommée
d’après le nom des îles situées à l’embouchure de la rivière Romaine
We hope that as you scan
through these Web pages, your imagination will take you back 80 Million
years - further than the mind can fully comprehend. What you will
discover are skeletal drawings and artists renditions of large marine
reptiles which existed in this area of Canada during the Cretaceous
Period. Go ahead! Start your excursion! We hope it will arouse your
curiosity sufficiently to bring you to our Museum to see the largest
collection of Marine Reptile Fossils in Canada
How do scientists explain the changes in
life forms, which are obvious in the record of fossils in rocks? Early
explanations were built around the idea of successive natural disasters
or catastrophes that periodically destroyed life. After each catastrophe,
life began anew. In the mid-nineteenth century, both Charles Darwin and
Alfred Wallace proposed that older species of life give rise to younger
ones. According to Darwin, this change or evolution is
caused by four processes: variation, over-reproduction, competition, and
survival of those best adapted to the environment in which they live.
Darwin's theory accounts for all of the diversity of life, both living
and fossil. His explanation gave scientific meaning to the observed
succession of once-living species seen as fossils in the record of
Earth's history preserved in the rocks.
Scientific theories are continually
being corrected and improved, because theory must always account for
known facts and observations. Therefore, as new knowledge is gained, a
theory may change. Application of theory allows us to develop new plants
that resist disease, to transplant kidneys, to find oil, and to
establish the age of our Earth. Darwin's theory of evolution has been
refined and modified continuously as new information has accumulated.
All of the new information has supported Darwin's basic concept--that
living beings have changed through time and older species are ancestors
of younger ones.
The Law of Fossil Succession
is very important to geologists who need to know the ages of the rocks
they are studying. The fossils present in a rock exposure or in a core
hole can be used to determine the ages of rocks very precisely. Detailed
studies of many rocks from many places reveal that some fossils have a
short, well-known time of existence. These useful fossils are called index fossils.
Today the animals and plants that live
in the ocean are very different from those that live on land, and the
animals and plants that live in one part of the ocean or on one part of
the land are very different from those in other parts. Similarly, fossil
animals and plants from different environments are different. It becomes
a challenge to recognize rocks of the same age when one rock was
deposited on land and another was deposited in the deep ocean.
Scientists must study the fossils from a variety of environments to
build a complete picture of the animals and plants that were living at a
particular time in the past.
The study of fossils and the rocks
that contain them occurs both out of doors and in the laboratory. The
field work can take place anywhere in the world. In the laboratory, rock
saws, dental drills, pneumatic chisels, inorganic and organic acids, and
other mechanical and chemical procedures may be used to prepare samples
for study. Preparation may take days, weeks, or months--large dinosaurs
may take years to prepare. Once the fossils are freed from the rock,
they can be studied and interpreted. In addition, the rock itself
provides much useful information about the environment in which it and
the fossils were formed.
Comment parler de préhistoire en Touraine
sans évoquer les ateliers de taille du silex de la région du Grand-Pressigny?
Là, sur le territoire de plusieurs communes du bassin de la Claise et de
la Creuse, les hommes du Néolithique final, il y a environ 4500 ans, ont
exploité les grandes dalles de silex du Turonien supérieur pour
confectionner des lames dont les plus grandes atteignent 35 cm. Ces
grandes lames furent obtenues à partir de nucléus d'un type particulier
appelés "livres de beurre", selon une méthode nécessitant un haut degré
de technicité. Les lames pressigniennes, transformées en couteaux, en
poignards, en faucilles, ..., ont été retrouvées bien au-delà de leur
lieu de fabrication, jusqu'en Belgique ou dans les cités lacustres de
Suisse, par exemple.
Si j'ai commencé cette section par cette évocation, c'est parce
que je souhaite faire une distinction avec les sections concernant les
fossiles. Si, à mon sens, à part quelques cas particuliers, la récolte
des fossiles en Touraine ne pose pas de graves problèmes vis-à-vis du
patrimoine collectif (dans le cas des faluns du bassin de Savigné, la
présence de nombreux collectionneurs fut même bénéfique en regard de
l'exploitation intensive des gisements), il n'en va pas de même pour les
ateliers pressigniens. A chaque labour, les engins agricoles remontent
en surface des résidus de taille du silex : éclats ou nucléus "livres de
beurre", mais aussi parfois des fragments de lames ou des outils. Or,
certains de ces ateliers de taille seront probablement un jour fouillés
scientifiquement afin de mieux comprendre ce qui s'est passé ici il y a
4500 ans et chaque pièce récoltée par un collectionneur est perdue pour
la science.
Paleodictyoptera:
Dunbaria fasciipennis Tillyard in Dunbar & Tillyard 1924. This
insect, with its beautifully-patterned wings and long cerci (the "tails"),
had a wingspan of about 37 mm. It flew some 260 million years or so ago
over what are today the prairies of central Kansas. This image is a
scan of the original glass plate negative used for the type description
of the species. Scan courtesy of and used with the permission of the
Cawthron Institute, Nelson, New Zealand, which is where Robin J.
Tillyard, one of the great insect paleontologists and entomologists,
worked when he studied the Yale collection of Kansas Elmo fossils.
Thanks to Rod Asher of The Cawthron Institute for scanning the images
for me.
Plants and animals go
through certain changes after death. If not immediately preserved in a
medium, they will usually decay or be degraded through the feeding
action of bacteria or scavenging animals or through chemical action. If
the organism becomes imbedded in a preserving medium, fossilization
occurs. This process of fossilization is termed taphonomy (Efremov,
1940).
This catalogue lists the following forms of preservation or media in
which fossil Diptera have been found: body fossils including amber,
compression and impression, copal, permineralization, sediment recovery,
and tar pit recovery; and trace fossils.
Amber and Copal:
In amber and copal specimens, an organism becomes entrapped over a
relatively short period of time in the various plant resins [exuded from
trees such as Agathis, Araucaria (Araucariaceae),
Bursera, Protium (Burseraceae), Hymenaea (Fabaceae),
Liquidambar (Hamamelidaceae), Pinus (Pinaceae), Shorea
(Dipterocarpaceae), and various Taxodiaceae-see Langenheim (1969) for a
detailed breakdown of plant sources] that form copal and amber [Schlüter
(1990) and Henwood (1992a) give detailed accounts of the imbedding
process for specimens in amber and Pike (1993) and Henwood (1993)
discuss taphonomy and collecting bias]. Though what is found in these
amber and copal media is the actual specimen that died from thousands to
millions of years ago, in many specimens, some amount bacterial action
may have taken place over time and membranous material supporting the
exoskeletal sclerites is often missing. Thus, when one attempts to
recover the entrapped specimen by dissolving the amber or copal in a
solvent, the result is often a disappointing slurry of floating
chitinous plates. However, in some specimens preserved in this fashion,
little or no decay has taken place and some muscle tissue complete with
mitochondria survives and DNA can still be recovered (Henwood, 1992b).
This had led to the exciting field of paleomolecular entomology in which
the DNA of fossil organisms over 100 million years old can be studied
and comparisons made with putative extant relatives.
Compression and Impression Fossils:
Two-dimensional compression fossils normally encounter some sort of
mineral substitution during the fossilization process. Most often,
solution and other chemical action under water transform the composition
of insect tissue and exoskeleton into a thin film of carbon. When this
type of alteration of the composition of the hard parts of insect tissue
occurs (called carbonization), normally only major features such as the
head, thorax, abdomen, and larger appendages are visible, but in two
dimensions. In addition to the difficulty in identifying a specimen in
two dimensions, the compression process as well as the process of
mineral replacement can lead to a great deal of distortion of various
body features. Heads, thoraces, and abdomens can often look like parts
of insects that have been squashed on cards or abdomens will be bloated
due to a long period of submersion in liquid before any amount of
sedimentation took place to preserve the specimen. Wings and their
venation generally are the parts of the insect least subjected to this
distortion and, if in good condition, are the major identifiable
features of Diptera compression fossils.
When the original organic or replaced mineral material exfoliates from
the fossil leaving only an imprint on the sedimentary matrix, this is
called an impression.
Permineralization:
In some cases, chemical replacement occurs of an entire specimen in
which all parts of the insect are visible in three dimensions after acid
extraction of the specimen from the mineralized nodule in which it had
become imbedded. One type of permineralization, silicification, is found
in fossils from Böttinger Marmor in Switzerland and the Calico Mountains
and other desert and semi-desert montane environments in southern
California where organisms in heavily mineralized Miocene sinter
environments became embedded in silicified nodules over time, the
mineral of which replaced the chitinous portions of the insect. This
form of fossilization results in a remarkably well preserved specimen in
which even the smallest setae (now silicified) can still be observed on
various portions of the insect exoskeleton. Palmer & Bassett (1954) and
Pierce (1960) discuss the process and resulting faunal discoveries in
more detail.
Other examples of permineralization include hematitization (Parachute
Creek, Colorado-Eocene), and pyritization (Bognor Regis, England-Lower
Eocene).
Trace fossils, ichnofossils, or "Lebenspurren", are structures in
sediment or other biological materials (e.g., wood, leaves, roots, etc.)
left by living organisms. Trace fossils give evidence that a particular
type of organism was occupying a specific medium at one time. Most trace
fossils are examples of the work of an organism
JS
Il
existe deux principaux types de fossiles : les restes d'organismes fossilisés et
les empreintes fossiles.
Les
restes fossilisés
peuvent comprendre n'importe quelle partie de l'animal ou de la plante en
question. Par exemple, les os, les dents, les coquilles et les feuilles sont
considérés comme des restes fossilisés.
Les
empreintes fossiles
sont les traces de
l'existence passée d'animaux. Ces empreintes peuvent inclure des traces de
pas ou d'enfouissement et des crottes fossilisées.
Découvrez sur ce site
les travaux de Harun Yahya qui réfutent totalement le
darwinisme, les dernières actualités et analyses démontrant
l’impact de ses travaux au niveau planétaire.
The number of living fossils that
literally silence Darwinism is in the millions. Some of
these are stored in warehouses. Only a very few are on
display in various museums. This site has been prepared in
order to put an end to the mentality that causes these
fossils, that represent a complete response to Darwinism, to
be hidden away, and that prevents them from being placed
before the public
Le but de ce site
est de présenter le plus grand nombre possible de photos de coquilles
fossiles (gastropodes et bivalves) du tertiaire, afin de permettre à chacun
de découvrir la diversité et la beauté de ces fossiles.
Un autre but est de faciliter l´identification par des amateurs. Pour cela,
les photos sont organisées en base de données. Chaque photo possède une
notice comportant de nombreuses informations, dont les renseignements
taxonomiques tirés de la base de données de référence du
Museum d´Histoire Naturelle,
la localisation, la taille... Soyez toutefois bien conscients des limites de
l'identification sur photo, qui ne remplace ni l'exemplaire en main ni la
lecture des diagnoses.
Un
fossile est le reste (coquille, os, dent, graine,
feuilles...) ou simple moulage d'un animal ou d'un végétal
conservé dans une roche sédimentaire. Les fossiles et les
processus de fossilisation sont étudiés principalement dans
le cadre de la
paléontologie.
Suivant les espèces et
les périodes, les fossiles peuvent être de différentes
qualités et plus ou moins abondants. Le processus de
fossilisation est exceptionnel, et les témoignages que nous
apportent les fossiles sur plus de trois milliards d'années
d'évolution
de la vie sur
Terre
sont encore lacunaires et le resteront certainement.
Dans la Drôme, les
terrains sédimentaires que l'on peut rencontrer sont compris pour
la plupart entre le Bathonien (Jurassique moyen, 166 millions
d'années) et le Plaisancien (Pliocène supérieur, 1,8 million
d'années). On trouve également quelques petits affleurements datés
du Trias (200 - 235 millions d'années), et de l'ère quaternaire (moins
de 1,8 million d'année), mais ceux-ci ne sont pas intéressants
pour la recherche de fossiles Les terrains de l'ère
secondaire s'étendent du Bathonien (Jurassique moyen, 166 M.A.) au
Santonien (crétacé supérieur, 83 M.A.).
Slide 5:
Acknowledgments Many persons have helped us as we assembled this
report. We gratefully recognize artist Julie De Atley for the graphic
design and illustration, photographer George James, Robert E. Weems (who
provided the fossil footprints), and Julia A. Jackson, Editor. We also
extend our sincerest thanks and appreciation to the following individuals
for reviewing the manuscript: David Applegate Patricia H. Kelley Kevin
Padian American Geological Institute University of North Carolina,
University of California, Berkeley Wilmington Mel M. Belsky Kim L. Pojeta
Brooklyn College, CUNY Christopher G. Maples Smithsonian Institution
Indiana University, Bloomington David J. Bohaska Linda Pojeta Smithsonian
Institution Sara Marcus Northport, New York University of Kansas Alan H.
Cheetham Robert W. Purdy Smithsonian Institution James G. Mead Smithsonian
Institution Smithsonian Institution Daniel Dreyfus Vicki Quick and her
students Smithsonian Institution Marcus E. Milling Marshall, VA American
Geological Institute J.T. Dutro, Jr. Bruce N. Runnegar U.S. Geological
Survey Don Munich University of California, Los Angeles Charlestown, IN
Alan Goldstein Judy Scotchmoor Falls of the Ohio State Park, Charles
Naeser University of California, Berkeley Clarksville, IN U.S. Geological
Survey Colin D. Sumrall Pat Holroyd Norman D. Newell Cincinnati Museum of
Natural University of California, Berkeley American Museum of Natural
History History and Science John Keith William A. Oliver, Jr. Frank C.
Whitmore, Jr. U.S. Geological Survey U.S. Geological Survey U.S.
Geological Survey The American Geological Institute and The Paleontologial
Society thank the following organizations for supporting the production
and distribution of Evolution and the Fossil Record. Publishing Partners
Supporters Paleontological Research Institution Association for Women
Geoscientists Howard Hughes Medical Institute National Association of
Geoscience Teachers California Science Teachers Association SEPM (Society
for Sedimentary Geology) University of California Museum of Paleontology
The Society for Organic Petrology Society of Vertebrate Paleontology
Sponsors Soil Science Society of America American Institute of Biological
Sciences American Association of Petroleum Geologists Society for the
Study of Evolution American Geophysical Union Cleveland Museum of Natural
History Geological Society of America Denver Museum of Nature and Science
California Academy of Sciences E V O L U T I O N A N D T H E F O S S I L R
E C O R D iii
Slide 6:
Foreword v Geologic time chart vi Contents Introduction 1 The
Fossil Record 3 Change Through Time 4 Darwin’s Revolutionary Theory 6 A
Mechanism for Change 10 The Nature of Species 11 The Nature of Theory 12
Paleontology, Geology, & Evolution 13 Dating the Fossil Record 16 Examples
of Evolution 18 Summary 23 Glossary 24 References/Readings 26 iv E V O L U
T I O N A N D T H E F O S S I L R E C O R D
Slide 7:
Foreword Evolution is one of the fundamental underlying concepts
of modern science. This powerful theory explains such phenome- na as the
history of life preserved in the fossil record; the genetic, molecular,
and physical similarities and differences among organ- isms; and the
geographic distribution of organisms today and in the past. Indeed,
evolution forms the foundation of modern biology and paleontology and is
well documented by evidence from a variety of scientific disciplines.
Evolution is also one of the most misunderstood and controversial concepts
in the eyes of the general public. This situation is unfortunate, because
the controversy surrounding evolution is unnecessary. Resistance to
evolution stems in part from misunderstanding science and how it is
distinct from religion. Science and religion provide different ways of
knowing the Earth and universe. Science proceeds by testing hypotheses and
thus is restricted to natural, testable expla- nations. By definition,
science is unable to confirm or deny the existence or work of a Creator;
such questions are beyond the realm of science. As a scientific concept,
evolution therefore can make no reference to a Creator. Many people of
faith, including scientists, find no conflict between evolution and their
religion; in fact, many religious denominations have issued statements
supporting evolution. Science and religion need not conflict. Numerous
lines of evidence show that life has changed through time. Evolution is
the best scientific explanation for this change. This booklet describes a
small portion of the evidence for this change, especially as documented by
the fossil record, and outlines the processes involved in evolution. Many
fascinating questions remain concerning the history of life and the
process through which it has developed. As we continue to learn about life
on Earth, the theory of evolution will itself evolve. That is the strength,
adventure, and excitement of doing science! Patricia H. Kelley
Paleontological Society President, 2001-2002 Marcus E. Milling AGI
Executive Director E V O L U T I O N A N D T H E F O S S I L R E C O R D v
Slide 8:
Boundaries ~ Million Years Ago Holocene 0.01 Quaternary Modern
humans Pleistocene 2 Pliocene Neogene 5 Cenozoic Miocene Tertiary 23
Mammals diversify; Oligocene early 34 hominids Paleogene Eocene 55
Paleocene 65 Flowering plants common; Cretaceous major extinction
including dinosaurs & ammonoids Mesozoic Phanerozoic 144 Early birds &
mammals; Jurassic abundant dinosaurs 206 Abundant coniferous trees,
Triassic first dinosaurs; first mammals 250 Mass extinction of many marine
animals Permian including trilobites 290 Carboniferous Pennsylvanian Fern
forests; insects; first 314 reptiles; crinoids; sharks; large primitive
trees Mississippian 360 Paleozoic Devonian Early tetrapods, ammonoids, &
trees 409 Silurian Early land plants & animals 439 Ordovician Early Fish
500 Abundant marine invertebrates; Cambrian trilobites dominant 540
Single-celled and, later, multi-celled, Proterozoic soft-bodied organisms;
first invertebrates “Precambrian” 2,500 Oldest fossils; bacteria Archean &
other single-celled organisms Oldest known fossils 3,800 iv E V O L U T I
O N A N D T H E F O S S I L R E C O R Although D these dates have an
accuracy range of about +/– 1%, boundary dates continue to change as
geoscientists examine more rocks and refine dating methods.
Slide 9:
Tyrannosaurus no longer stalks its prey across North America.
There are no pterosaurs sailing majesti- cally overhead. Trilobites no
longer crawl on the sea floors of Earth. Today, other predators roam in
search of a meal. Birds soar the skies, and crabs scuttle across the ocean
bed. Life on Earth has changed through time. It has evolved. Change
through time is a widely accepted meaning of the word evolution. We speak
of the evolution of the English language, the evolution of the automobile,
or the evolution of politics in the United States. In natural history,
biological or organic evolution means change in populations of living
organisms on planet Earth through time. Charles Darwin defined biological
evolution as “descent with modification,” that is, change in organisms in
succeeding generations. Another way of saying this is, “species of
organisms originate as modified descendants of other species” (Hurry,
1993). Biological evolution is the derivation of new species from
previously existing ones over time. Evolution is the central unifying
concept of natural history; it is the foundation of all of modern
paleontology and biology. This booklet presents a non-technical
introduction to the subject of evolution. Here you will find
straightforward definitions of important terms as well as discussions of
complex ideas. This brief introduction to the rich and fascinating history
of the theory of evolution cannot present in detail the vast body of
evidence that has led to the current understanding of evolutionary
processes. Our aim is to provide a sense of the history, strength, and
power of this important scientific theory. We hope that this booklet will
help you sense the wonder and excitement that paleontologists and other
students of evolutionary science feel when they contemplate the long and
intricate history of life on Earth. Earth. E V O L U T I O N A N D T H E F
O S S I L R E C O R D 1
Slide 10:
Lower Pliocene Changes in Chesapecten Chesapecten the fossil
scallop septenarius madisonius Chesapecten through about 13 million years,
shown particularly by the variation in the ‘ear’ Chesapecten on the upper
right of jeffersonius each shell (see arrows) and in the ribs on the shell.
Modified Chesapecten from Ward and middlesexensis Blackwelder (1975).
Upper Miocene Chesapecten middlesexensis Chesapecten santamaria
Chesapecten Middle Miocene nefrens Chesapecten coccymelus Chesapecten 2 E
V O L U T I O N A N D T H E F O S S I L R E C O R D sp.
Slide 11:
Fossils provide the dimension of time to The Fossil Record the
study of life For at least 300 years, scientists have been gathering the
evidence for evolutionary change. Much of this vast database is
observational, and the evidence came to light with the study offossils (paleontology)
and the rock record (geology). This essay focuses on the evidence about
evolution from the fossil record. Documentation of ancestor-descendant
relationships among organisms also comes from the fields of biogeography,
taxonomy, anatomy, embryology and, most recently, genetics — particularly
DNA analysis. Information from these fields can be found in the materials
listed in the “Suggested Readings.” Thefossil record remains first and
foremost among the databases that document changes in past life on Earth.
Fossils provide the dimension of time to the study of life. Some of the
most basic observations about fossils and the rock record were made long
before Darwin formulated his theory of “descent with modification.” The
fossil record clearly shows changes in life through almost any sequence of
sedimentary rock layers. Successive rock layers contain different groups
or assemblages of fossil species. Sedimentary rocks are, by far, the most
common rocks at Earth’s surface. They are formed mostly from particles of
older rocks that have been broken apart by water, ice, and wind. The
gravel, sand, and mud, which are collectively called particles of sediment,
settle in layers at the bottoms of rivers, lakes, and oceans. Shells and
other limy materials may accumulate in the oceans. As the sediments
accumulate they bury shells, bones, leaves, pollen, and other bits and
pieces of living things. With the passing of time, the layers of sediments
are compacted by the weight of overlying sediments and cemented together
to become the sedimentary rocks called limestone, shale, sand- stone, and
conglomerate. The buried plant and animal remains become fossils within
the sedimentary layers. E V O L U T I O N A N D T H E F O S S I L R E C O
R D 3
Slide 12:
Change Trilobite (Cambrian) Through Time The geological time-period
terms Cambrian, Ordovician, ...,Jurassic,..., Cretaceous, and on through
the Quaternary, define successive changes in species of animals and plants
through time on Earth. Thus, Ordovician trilobites differ from fish differ
from Jurassic and Cretaceous fish, Devonian trilobites, Silurian and
Devonian Mesozoic mammals differ from Cenozoic mammals, and so forth. In
addition to changes occurring in many different species found in different
geological time inter- vals, whole groups of organisms that were once
abundant and diverse, such as trilobites, can become extinct. The
boundaries between the great blocks of geologic time called Eras are
defined by major changes in the types of fossils found in the rocks
deposited in those Eras: Tyrannosaurus rex Paleozoic means “ancient
animals,” (Cretaceous) Brachiopod Mesozoic means “middle animals,” and
Cenozoic means (Devonian) “recent animals.” Trilobites and shelled animals
called brachiopods are common and typical Paleozoic fossils. Dinosaurs,
certain large marine reptiles, such as ichthyosaurs and mosasaurs, and
pterosaurs are found the flying reptiles called only in Mesozoic rocks.
Fossils of mammals, clams, snails, and bony fishes are typical of Cenozoic
fossil assemblages. Some species can be found on both sides of a time
boundary; however, the overall assemblage of organisms found in the rocks
of a given age is recognizably different from the assemblages found in the
rocks above and below. 4 E V O L U T I O N A N D T H E F O S S I L R E C O
R D
Slide 13:
Four species of Devonian trilobites (upper row) compared with
four species of Ordovician trilobites (lower row). Size varies from 1 inch
(25 mm) to 4 inches (100 mm). Modified from Moore (1959). E V O L U T I O
N A N D T H E F O S S I L R E C O R D 5
Slide 14:
Darwin’s Revolutionary Theory Charles Darwin used information
from several disciplines in developing his theory of evolution. He was
particularly impressed by the amount of variation that occurs within
living species, especially in domestic animals, and he spent a great deal
of time studying breeding programs. Even in Darwin’s 1809-1882 day, the
human effort in breeding variants of domestic animals had resulted in many
breeds of dogs, cats, horses, sheep, and cattle. As an example, consider
the tremendous variation in domestic dogs. The Chihuahua and the Saint
Bernard are about as different in size, shape, hair length, and other
features as one could imagine; yet both breeds are domestic dogs with the
scientific name Canis familiaris. The differences between them were
produced by human-engineered selective breeding programs. Artificial selec-
tion is the term for what we do when we choose plants and animals with
desirable features and breed them to produce or enhance these features in
their offspring. As different as they look, Chihuahuas and Saint Bernards
... and Poodles, Pomeranians, Pekinese...all domestic dogs share the same
gene pool. This shared gene pool means that all dogs have the ability to
interbreed, and this is why all domestic dogs are placed in one species.
The common gene pool of dogs also allows for the great definition of
species in animals variation we see in “man’s best friend.” A standard is
the ability to interbreed and produce fertile offspring. Birkenia
Drepanaspis Early Devonian Pteraspis Late Silurian Early Devonian 6 E V O
L U T I O N A N D T H E AnglaspisR F O S S I LR E C O D Late Silurian
Slide 15:
C h a r l e s D a r w i n Darwin gathered data and honed his
theory for 20 years before pub- lishing his well-known book in 1859, The
Origin of Species by Means of C harles Darwin was born in Shrewsbury,
England. He began studying medicine at Natural Selection, or The
Preservation of Favoured Races in the Struggle for Edinburgh University at
age Life. Darwin and his fellow naturalist Alfred Wallace independently
came 16, but his interests changed. to theconclusion that geologically
older species of life gave Ultimately he went to rise to geologically
younger and different species through the Cambridge University and pre-
process of natural selection. pared to become a clergyman. After receiving
his degree, Darwin accepted an invitation Darwin’s theory of evolution can
be summarized in four statements. to serve as an unpaid naturalist 1.
Variation exists among individuals within species. on the H.M.S. Beagle,
which Anyone who looks at their friends and relatives, or their pets, can
see varia- departed on a five-year scien- tion. Breeders of animals and
plants use these diverse characteristics to tific expedition to the
Pacific establish new varieties of dogs, cats, pigeons, wheat, cotton,
corn, and coast of South America on other domesticated organisms.
Scientists who name and classify plants and December 31, 1831. animals are
acutely aware of variation in natural pop- The research resulting from
this voyage formed the ulations. For example, the level of resistance to
basis of Darwin’s book, The insecticides varies among individuals within
Origin of Species by Means of species of insects. This variation enables
Natural Selection (1859), in some individuals to survive application of
which he outlined his theory of insecticides and produce offspring
evolution, challenging the con- that inherit this resistance to these
temporary beliefs about the insecticides. creation of life on earth. 2.
Organisms produce mo ore Fish Fossil (Eocene) offspring than the
environment can support. All living things produce more individuals than
can survive to maturity. Think of the thou- sands of acorns that one
mature oak tree produces every year. A female salmon produces about
28,000,000 eggs when spawning. One oyster can Fish diagram was modified
from Fenton and Fenton (1958) and Romer (1966). Endeiolepis Late Devonian
Osmeroides Cretaceous Dapedius E V O L U T I O N A N D T H E F O S S I L R
E C O R D 7 Jurassic
Slide 16:
produce 114,000,000 eggs in a single spawning. Darwin calculated
that in elephants, which are among the slowest breeding land mammals, if
all of the potential young of a single female survived and reproduced at
the L same rate, after 750 years the descen- ate Triassic and Jurassic
dants of this single mother could mammals were small. Most number
19,000,000! Clearly, if all of Early Jurassic mammal were about the size
of a Modified from Jenkins and Parrington (1976). these seeds, eggs, and
young survived mouse; a few attained to become adults who also reproduced,
the world would soon be overrun with oak trees, salmon, domestic cat size.
Most were oysters, and elephants. insect eaters or omnivores; a 3.
Competition exists among individuals. Regardless of few were probably
herbivores. the rate of reproduction in a species, all of the young do not
survive to By Cretaceous time, mam- become reproducing adults. This fact
indicates that large numbers of off- mals the size of opossums spring
somehow are eliminated from the population. Some certainly die by occur in
the fossil record; accident. But most of them succumb to competition with
other individuals. The most intense competition may be among individuals
of the same species these existed with mouse- who compete for nearly
identical environmental requirements. Competition sized animals that were
the may be as simple as a race to get a rabbit — the first fox there gets
lunch; ancestors of living marsupials the others go hungry. Competition
may involve obtaining a choice nesting and placentals. In early site, or
being able to find the last available hiding hole when a bigger fish
Cenozoic time, mammals comes looking for dinner. Those individuals who
catch the rabbit or find underwent a tremendous the hiding hole survive to
pass on their genes to the next generation. radiation and diversification.
Pholidota Rodentia Primates Modified from Novacek (1994). Monotremata
Marsupialia Edentata Lagomorpha Macroscelidea Scandentia 0 10 Cenozoic 20
Oriental 30 Tree Palaeoryctoids Shrew 40 Multituberculata Million Years
Ago 50 60 Rabbit Squirrel Elephant Ape Anteater Scaly 70 Rat Shrew Monkey
Armadillo Anteater Triconodonts Mouse Lemur 80 Beaver Human Mesozoic 90
Groundhog 100 Extinct Platypus Kangaroo 110 Opossum 8 E V O L U T I O N A
N D T H E F O S S I L R E C O R D 120 Koala 130
Slide 17:
4. The organisms whose variations best fit them to the
environment are the ones who are most likely to survive, reproduce, and
pass those desirable variations on to the next generation. Many of the
natural variations we observe in species do not seem to be either
particularly helpful or particularly harmful to an individual in its
struggle for survival. Hair and eye color may be such neutral variations
in human beings. Some variations certainly lower the chances of survival,
such as hemophilia in mammals, albinism in many wild animals, or an
unusually thin shell in clams living where there are numerous hungry
snails. Some variations are helpful. For example, any variation that
increases an antelope’s speed may help it elude predators. Any variation
that increases water retention in a desert plant will favor survival of
that plant to reach maturity. Those animals and plants that survive to
maturity and are able to reproduce become the parents of the next
generation, passing on the genes for the successful variation. Darwin
called the process by which favorable variations are passed from
generation to generation natural selection. He made many important
observations on the relation- ship of individual variation to survival.
During his stay in the Galapagos Islands, Darwin noted that the
populations of tortoises on each island had physical features so
distinctive that people could often tell from which island an animal came
simply by looking at it. We commonly hear natural selection referred to as
“survival of the fittest.” This popu- lar phrase has a very specific
biological meaning. “Fittest” means that organisms must not only survive
to adulthood, they must actually reproduce. If they do not reproduce,
their genes are not passed on to the next generation. Evolution occurs
only when advantageous genetic variations are passed along and become
represented with increasing frequency in succeeding generations.
Dermoptera Insectivora Artiodactyla Tubulidentata Hyracoidea Chiroptera
Carnivora Cetacea Proboscidea Sirenia Perissodactyla Creodonta
Condylarthra Aardvark Desmosrylia Flying Squirrel Bat Embrithopoda Sea Cow
Hyrax Camel Whale Horse Elephant Deer Dolphin Zebra Lion Hedgehog Giraffe
Porpoise Rhinoceros Tiger Mole Cat Cow Shrew Dog Pig Sea Lion Goat Bear
Seal E V O L U T I O N A N D T H E F O S S I L R E C O R D 9
Slide 18:
A Mechanism for Change Biological evolution is not debated in the
scientific community — organ- Shark’s Tooth (Paleocene) isms become new
species through modification over time. “No biologist today would think of
submitting a paper entitled ‘New evidence for evolution;’ it simply has
not been an issue for a century” (Futuyma, 1986). Precisely how and at
what rates descent with modification occurs are areas of intense research.
For example, much work is under way testing the significance of natural
selection as the main driving force of evolution. Non-Darwinian
explanations such as genetic drift have been explored as additional
mechanisms that explain some evolutionary changes. Darwin proposed that
change occurs slowly over long periods of geologic time. In contrast, a
Modern Fern more recent hypothesis called punctuated equilibrium proposes
that much change occurs rapidly in small isolated populations over
relatively short periods of geologic time. In Darwin’s time, the nature of
inheritance and the cause of variation were very poorly understood. The
scientific understanding of heredity began with the work of Gregor Mendel
in the 1860s in Brno, Czech Republic. This understanding accelerated
throughout the 20th century and now includes knowledge of chromosomes,
genes, and DNA with Fossil Seed Fern (Pennsylvanian) its double helix.
Evolution could not occur without genetic variation. The ultimate source
of variation can now be understood as changes or mutations in the sequence
of the building blocks of the genetic material carried on the chromosomes
in eggs and sperm. Many of these changes occur spontaneously during the
process of creating copies of the genetic code for each egg or sperm. For
example, the wrong molecule may become attached to the newly formed strand
of DNA, or the strand may break and a portion can be turned around.
Certain forms of radiation and chemical toxins can also cause mutations in
the DNA. Because the sequence of building blocks in DNA is the genetic
foundation for the development of an individual’s features or
characteristics, changes in the sequence can lead to a change in the
appearance or functioning of an individual with that mutation. 10 E V O L
U T I O N A N D T H E F O S S I L R E C O R D
Slide 19:
Although some changes may prove to be harmful or fatal, other
changes produce variations that convey a survival advantage to the
organism. It is these variations, when passed on, that give advantages to
the next generation. The Nature of Species Individuals change throughout
their lifetimes; they grow, receive injuries, color their hair, or pierce
their eyebrows. These changes are not evolutionary, because they cannot be
inherited by the next generation. The changes are lost when the individual
possessing them dies. Individuals do not evolve, only populations evolve.
Species evolve over successive generations as their local populations
interbreed and change. The a species is a group of biological definition
of a species embodies this concept: naturally occurring populations that
can interbreed and produce offspring that can interbreed. This point is
very important: species always con- sist of changing and interbreeding
populations. There never was a first ‘saber-toothed cat,’ ‘first mastodon,’
or ‘first dinosaur.’ Instead, there was a first population of
interbreeding individuals that we call ‘saber-toothed cats,’ or ‘mastodons,’
or ‘dinosaurs.’ At any given time in the past, members of populations of a
species were capable of interbreeding. It is only with ‘20/20 hindsight,’
the perspective of time, that we designate the breaks between ancestor and
descendant species at a particular point. Although we can often test the
biological definition of species directly when studying populations of
living organisms, we cannot do the same with fossils. No matter how long
we watch, no two fossils will ever breed. Therefore, we must look for
other ways to deter- mine relatedness among fossil organisms. Because
genetically similar organisms produce similar physical features,
paleontologists can use the bones, shells, and other preserved body parts
to help us recognize species in the fossil record. Fossil Wood (Pleistocene)
E V O L U T I O N A N D T H E F O S S I L R E C O R D 11
Slide 20:
The Nature of Theory In the middle of the 19th century, Darwin
presented the world with a scientific explanation for the data that
naturalists had been accumulating for hundreds of years — the theory of
evolution. The term theory does not refer to a mere idea or guess.
Scientific theories provide interpretations of natural phenomena and
processes so that they are understandable in terms science, as opposed to
of human experience. In common usage, the term theory is applied only to
an interpretation or explanation that is well-substantiated by evidence.
Useful theories incorporate a broad spectrum of the information available
at the time the theory is proposed. Facts, inferences, natural laws, and
appropriate well-tested hypotheses are all part of the construction of a
strong theory. Thus, a theory is very different from a belief, guess,
speculation, or opinion. Scientific theories are continually modified as
we learn more about the universe and Earth. Let’s look at three examples.
➣ In 18th century science, combustion was explained by a complex theory
having to do with the supposed presence of an undetectable substance
called phlogiston. Then Joseph Priestley discovered oxygen and Antoine
Lavoisier showed that fire was not a material substance or element, it was
the combining of a substance with oxygen. The phlogiston theory was
abandoned. ➣ In the 20th century, the theory of continental drift was a
step in the direction of recognizing that continents change their
geographic positions through time. Continental drift was succeeded by the
much more comprehensive theory of plate tectonics, which provided a
mechanism for movement of continents, opening and closing of ocean basins,
and formation of mountains. 12 E V O L U T I O N A N D T H E F O S S I L R
E C O R D
Slide 21:
➣ People once thought that diseases were caused by evil spirits,
ill humors, or curses. The term The germ theory showed that many diseases
are caused by microbes. In turn, the germ theory theory of disease has
been modified as we have learned that diseases can be caused by does not
things other than germs, such as dietary deficiencies and genetic factors.
refer to a Notice that while a particular theory may be discredited or
modified, still-valid observational and experimental data, as well as our
knowledge of natural laws, are not mere idea abandoned; they are
incorporated in a new or revised theory. We have tested some observations
so thoroughly that we accept them as facts. For or guess example, we
consider it a fact that the sun appears in the eastern sky each morning or
that an object released from the top of a building will fall to Earth.
Some explanations are so strongly supported by facts, and describe so well
some aspect of the behavior of the natural world, that they are treated as
scientific laws. Good examples of these include the laws of thermodynamics,
which govern the mechanical action or relations of heat; or the laws of
gravitation, which cover the interactions between objects with mass. We
continue every day to learn more about the world and the universe in which
we live. Thus, scientific theory is always subject to reaffirmation,
reinterpretation, alteration, or abandonment as more information
accumulates. This is the self-correcting nature of science; dogma does not
survive long in the face of continuous scrutiny of every new idea and bit
of data. When scientists do not understand how some aspect of our universe
operates, they do not assume an unknowable supernatural cause. They
continue to look for answers that are testable within the realm controlled
by natural laws as we understand them at any given moment. It may be years
or centuries before scientists unravel a particularly difficult problem,
but the search for answers never stops. This quest for understanding is
the wonder and excitement of science! Paleontology, Geology, and Evolution
Trilobite (Ordovician) Paleontologists generally come much too late to
find anything but skeletons. However, they find something denied to the
biologist — the time element. The crowning achieve- ment of paleontology
has been the demonstration, from the history of life, of the validity of
the evolutionary theory (paraphrased from Kurtén, 1953). E V O L U T I O N
A N D T H E F O S S I L R E C O R D 13
Slide 22:
In Darwin’s day, the fossil record was poorly known, but this is
no longer true. A major focus for geologists is establishing the times of
origin of the rock formations in the crust of Earth — the science of
geochronology. For paleontologists, it is important to Ammonite (Cretaceous)
know which rock formations were formed at the same time and thus can be
correlated, which rocks were formed at different times, and to put the
formations into a time sequence from oldest to youngest in any area under
study. Fossils are key to establishing the sequence of the ages of layered
sedimentary rocks, and they are the direct proof of the changes that have
occurred in living organisms through time on our planet. In the mid-1600s,
about 200 years before Darwin published his theory of evolution, the
Danish scientist Nicholas Steno found that it was possible to establish
the order in which layered rocks were deposited. He recognized that
particles of sand, mud, and gravel settle from a fluid according to their
relative weight. Slight changes in particle size, composition, or
transporting agent result in the formation of layers in the rocks; these
layers are also called beds or strata. Layering, or bedding, is the most
obvious feature of sedimentary rocks. The study of layered T esting the (sedimentary)
rocks is called stratigraphy. Sedimentary rocks are formed particle by
particle and bed by bed, and the layers Superposition are stacked one on
another. Thus, in any sequence of undisturbed layered rocks, a given
Principle bed must be older than any bed on top of it. This How old are
layers 3 and 4? Principle of Superposition is fundamental to understanding
the age of rocks; at any one Limestone #4 Youngest place it indicates the
relative ages of the rock Lava Flow layers and of the fossils they contain.
Because (80 mya) rock types such as sandstone, limestone, and Shale #3
shale are formed repeatedly through time, it is usually not possible to
use rock types alone to Sandstone #2 ) e ya ik determine the time in which
rock formations m D 5 te (8 ani Shale #1 Oldest were formed, or to
correlate them to other r G areas. To determine the age of most Zones of
Contact Metamorphism The oldest rocks, layers 1,2, and 3, were deposited
in succession, and they contain fossils that establish their relative age
as Late Cretaceous. The granite dike cutting through the shale (#1) and
sandstone (#2) must be younger as it shows contact metamorphism with those
rocks. Scientists verify this observation by using isotopic methods to
determine the age of the dike in years (85 mya). Since the dike is younger
than the shale and sandstone deposits, they must be older than 85 mya. The
lava flow on top of layer 3 has been dated isotopically at 80 mya.
Therefore, we can deduce that layer 3 and its fossils must have been
deposited between 80 and 85 mya. Contact metamorphism occurred when the
hot lava flowed onto layer 3, but there is none between the lava flow and
the lime- stone (#4). Why? The lava (80 mya) had cooled and solidified
before the limestone was deposited, 14 E V O L U T I O N and so layer 4
must be younger than 80 mya. A N D T H E F O S S I L R E C O R D
Slide 23:
P rinciple of sedimentary rocks, scientists study the fossils
they contain. Superposition — In the late 18th and early 19th centuries,
English geologists and French paleontologists discovered that the age of
rocks could be In any sequence of determined and correlated by their
contained fossils. Rocks of the same undisturbed layered age contain the
same, or very similar, fossil species, even when the rock units rocks, a
given bed extend over a large area or the exposures are not continuous.
They also noted that there was a distinct, observable succession of
fossils from older to younger must be older rocks that did not repeat
itself. These geoscientists were the first to use fossils to cor- than any
bed on relate the time of formation of the rocks in which the fossils
occur. Three concepts are top of it. important in the study and use of
fossils: (1) Fossils are the remains of once living organ- isms; (2) The
vast majority of fossils are the remains of the hardparts of extinct
organisms; they belong to species no longer living anywhere on Earth; (3)
The kinds of fossils found in rocks of different ages differ because life
on Earth has changed through time. If we begin at the present and examine
older and older layers of rock, we will arrive at a level where no human
fossils are found. If we continue backward in time, we successively come
to layers where no fossils of birds are present, no mammals, no reptiles,
no four-footed animals, no fishes, no shells, and no members of the animal
kingdom. These concepts are summarized in the general principle called the
Law of Fossil Succession. The kinds of animals and plants found as fossils
change through time. When we find the same kinds of fossils in rocks in
different places, we know the rocks are of the same age. Amphibians
Shelled Animals Mammals Humans Fishes Reptiles Birds Quaternary Tertiary
Stratigraphic Cretaceous ranges and Jurassic origins of Triassic some
major Permian groups of Pennsylvanian animals. Mississippian Modified from
Devonian Edwards and Pojeta (1994). Silurian Ordovician Cambrian E V O L U
T I O N A N D T H E F O S S I L R E C O R D 15
Slide 24:
Dating the Fossil Record The study of the sequence of occurrence
of fossils in rocks, biostratigraphy, reveals the relative time order in
which organisms lived. Although this relative time scale indicates that
one layer of rock is younger or older than another, it does not pinpoint
the age of a fossil or rock in years. The discovery of radioactivity late
in the 19th century enabled scientists to develop techniques for
accurately determining the ages of fossils, rocks, and events in Earth’s
history in the distant past. For example, through isotopic dating we’ve
learned that Cambrian fossils are about 540-500 million years old, that
the oldest known fossils are found in rocks that are about 3.8 billion
years old, and that planet Earth is about 4.6 billion years old.
Determining the age of a rock involves using minerals that contain
naturally-occurring radioactive elements and measuring the amount of
change or decay in those elements to calculate approximately how many
years ago the rock formed. Radioactive elements are Newly unstable. They
emit particles and energy at a relatively constant rate, transforming
themselves formed 100% crystal through the process of radioactive decay
into other elements that are stable — not radioactive. Radioactive
elements can serve as natural clocks, because the rate of emission or
decay is measurable and because it is not affected by external factors.
About 90 chemical elements occur naturally in the Earth. By definition an
element is a substance that cannot be broken into a simpler form by
ordinary chemical means. 75% 25% decayed The basic structural units of
elements are minute atoms. They are made up of the even tinier subatomic
particles called protons, neutrons, and electrons. To help in the
identification and classification of elements, scientists Parent Atoms
Remaining have assigned an atomic number to each kind of atom. The 50% 50%
atomic number for each element is the number of protons in decayed an atom.
An atom of potassium (K), for example, has 19 protons in its nucleus so
the atomic number for potassium is 19. 75% 25% decayed Modified from
Bushee and 96.88% others (2000). decayed 16 0 1 2 3 4 5 6 Half-Lives
Elapsed
Slide 25:
Although all atoms of a given element contain the same number of
protons, they do not contain the same number of neutrons. Each kind of
atom has also been assigned a mass number. That number, which is equal to
the number of protons and neutrons in the nucleus, identifies the various
forms or isotopes of an element. The isotopes of a given element have
similar or very closely related chemical properties but their atomic mass
differs. Potassium (atomic number 19) has several isotopes. Its
radioactive isotope potassium-40 has 19 protons and 21 neutrons in the
nucleus (19 protons + 21 neutrons = mass number 40). Atoms of its stable
isotopes potassium-39 and potassium-41 contain 19 protons plus 20 and 22
neutrons respectively. Radioactive isotopes are useful in dating
geological materials, because they In this outcrop of convert or decay at
a constant, and therefore measurable, rate. An unstable radioactive
Ordovician-age isotope, which is the ‘parent’ of one chemical element,
naturally decays to form a stable limestone and shale nonradioactive
isotope, or ‘daughter,’ of another element by emitting particles such as
near Lexington, KY, protons from the nucleus. The decay from parent to
daughter happens at a constant rate the oldest layer is called the half-life.
The half-life of a radioactive isotope is the length of time it takes on
the bottom and for exactly one-half of the parent atoms to decay to
daughter atoms. No naturally occur- the youngest on ring physical or
chemical conditions on Earth can appreciably change the decay rate of the
top, illustrating the Principle of radioactive isotopes. Precise
laboratory measurements of the number of remaining Superposition. The
atoms of the parent and the number of atoms of the daughter result in a
ratio that is rocks were deposit- used to compute the age of a fossil or
rock in years. ed one layer at a Age determinations using radioactive
isotopes have reached the point where they are time “from the bot- subject
to very small errors of measurement, now usually less than 1%. For example,
tom up” starting about 450 mya. Isotopic Age Dating Method Parent/Daughter
Isotopes Half-Lives Materials Dated Age Dating Range Shells, limestone,
Carbon (C)/Nitrogen (N) C-14/N-14 5,730 yrs. organic materials 100-50,000
yrs. Potassium (K)/Argon (Ar) K-40/Ar-40 1.3 billion yrs. Biotite, whole
100,000-4.5 billion yrs. volcanic rock Rubidium (Rb)/Strontium (Sr) Rb-87/Sr-87
47 billion yrs. Micas 10 million-4.5 billion+ yrs. Uranium (U)/Lead (Pb)
U-238/Pb-206 4.5 billion yrs. Zircon 10 million-4.5 billion+ yrs. Uranium
(U)/Lead (Pb) U-235/Pb-207 710 million yrs. Zircon 10 million-4.5 billion+
yrs. E V O L U T I O N A N D T H E F O S S I L R E C O R D 17
Slide 26:
minerals from a volcanic ash bed in southern Saskatchewan, Canada,
have been dated by three independent isotopic methods (Baadsgaard, et al.,
1993). The potassium/argon method gave an age of 72.5 plus or minus 0.2
million years ago (mya), a possible error of We humans 0.27%; the uranium/lead
method gave an age of 72.4 plus or minus 0.4 mya, a possible error of
0.55%; and the rubidium/strontium method gave an age of 72.54 plus or
minus created the 0.18 mya, a possible error of 0.25%. The possible errors
in these measurements are well under 1%. For comparison, 1% of an hour is
36 seconds. For most scientific investigations classification an error of
less than 1% is insignificant. scheme for As we have learned more, and as
our instrumentation has improved, geoscientists have reevaluated the ages
obtained from the rocks. These refinements have resulted in an life on
Earth, unmistakable trend of smaller and smaller revisions of the
radiometric time scale. This and we choose trend will continue as we
collect and analyze more samples. Isotopic dating techniques are used to
measure the time when a particular mineral where to within a rock was
formed. To allow assignment of numeric ages to the biologically based
components of the geologic time scale, such as Cambrian...Permian...Cretaceous...
draw the Quaternary, a mineral that can be dated radiometrically must be
found together with boundaries rocks that can be assigned relative ages
because of the contained fossils. A classic, real-life example of using
K-40/Ar-40 to date Upper Cretaceous rocks and fossils is described in Gill
and Cobban (1973). Examples of Evolution The fossil record contains many
well-documented examples of the transition from one species into another,
as well as the origin of new physical features. Evidence from the fossil
record is unique, because it provides a time perspective for understanding
the evolution of life on Earth. This perspective is not available from
other branches of science or in the other databases that support the study
of evolution. This section covers four examples of evolution from the
incredibly rich and wonderful fossil record of life on Earth. We’ve chosen
examples of vertebrates, animals with backbones, primarily because most of
us identify more easily with this group rather than with sassafras or
snails or starfish. However, we could have chosen any of many studies of
evolutionary changes seen in fossil plants, invertebrates — animals
without backbones such as the Chesapecten scallops (above), or single-celled
organisms. We’ll examine the evolution of legs in vertebrates as well as
the evolution of birds, mammals, and whales. 18 E V O L U T I O N A N D T
H E F O S S I L R E C O R D
Slide 27:
Comparison of homologous bones of the forelimbs (pectoral
appendages or arms) of a lobe-finned fish from central Pennsylvania (left)
with an amphibian-like tetrapod from Greenland (right). Both are right
limbs seen from the underside. H=upper arm bone or humerus; U and r=forearm
bones or ulna and radius; u and i=wrist bones or ulnare and inter- medium.
The hand and finger bones are dark. Modified from Daeschler and Shubin
(1998). Lobe-finned Fish Amphibian-like Tetrapod (Late Devonian-about 370
mya) (Late Devonian-about 364 mya) Evolution of vertebrate legs The
possession of legs defines a group of vertebrate animals called tetrapods
— as distinct from vertebrate animals whose appendages are fins, the
fishes. In most fishes, the thin bony supports of the fins are arranged
like the rays of a fan; hence these fishes are called ‘ray-finned’ fish.
Trout, perch, and bass are examples of living ray-fins. Certain fishes are
called ‘lobe-finned,’ because of the stout, bony supports in their
appendages. Lobe-finned fish first appear in the fossil record in early
Late Devonian time, about 377 mya. The bony supports of some lobe-finned
fishes are organized much like the bones in the forelimbs and hind limbs
of tetrapods: a single upper bone, two lower bones, and many little bones
that are the precursors of wrist and ankle bones, hand and foot bones, and
bones of the fingers and toes that are first known in Late Devonian
amphibian-like animals from about 364 mya. These animals were the first
tetrapods. Many similarities also exist in the skull bones and other parts
of the skeleton between Devonian lobe-finned fishes and amphibian-like
tetrapods. In fact, in certain fossils the resemblances are so close that
the definition of which are fish and which are tetrapods is hotly debated.
In 1998, a lobe-finned fish was described from Upper Devonian rocks from
about 370 mya in central Pennsylvania (Daeschler and Shubin, 1998). This
fish has bones in its forelimb arranged in a pattern nearly identical to
that of some Late Devonian amphibian-like tetrapods. The pattern includes
a single upper-a
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