A Selected Chronological Bibliography of Biology and Medicine


 Part 1A


c. 13.75 G — 1636



Compiled by James Southworth Steen, Ph.D.

Delta State University


Dedicated to my loving family


This document celebrates those secondary authors and laboratory technicians without whom most of this great labor of discovery would have proved impossible.


Please forward any editorial comments to: James S. Steen, Ph.D., Professor Emeritus, jsteen08@bellsouth.net




“Reason was born, as it has since now discovered, into a world already wonderfully organized, in which it found its precursor in what is called life, its seat in an animal body of unusual plasticity, and its function in rendering that body’s volatile instincts and sensations harmonious with one another and with the outer world on which they depend.” George Santayana (1185).


“In all human affairs … there is a single dominant factor—time. To make sense of the present state of science, we need to know how it got like that: we cannot avoid an historical account…To extrapolate into the future we must look backwards a little into the past.” John M. Ziman (1501).


 "The proper concern of natural science is not what God could do if he wished, but what he has done; that is, what happens in the world according to the inherent causes of nature." Albertus Magnus; Alberti Magni; Albert of Cologne; Albert the Great (606; 1167).


"Admitting that vital phenomena rest upon physico-chemical activities, which is the truth, the essence of the problem is not thereby cleared up; for it is no chance encounter of physico-chemical phenomena which constructs each being according to a pre-existing plan, and produces the admirable subordination and the harmonious concert of organic activity.

There is an arrangement in the living being, a kind of regulated activity, which must never be neglected, because it is in truth the most striking characteristic of living beings. . . .

Vital phenomena possess indeed their rigorously determined physico-chemical conditions, but, at the same time, they subordinate themselves and succeed one another in a pattern and according to a law which pre-exists; they repeat themselves with order, regularity, constancy, and they harmonize in such manner as to bring about the organization and growth of the individual, animal or plant.

It is as if there existed a pre-established design of each organism and of each organ such that, though considered separately, each physiological process is dependent upon the general forces of nature, yet taken in relation with the other physiological processes, it reveals a special bond and seems directed by some invisible guide in the path which it follows and toward the position which it occupies.

The simplest reflection reveals a primary quality, a quid proprium of the living being, in this pre-established organic harmony.” Claude Bernard (174).




c. 13.75 G (giga-annum = billion years)

Georges Henri Joseph Édouard Lemaitre (BE) proposed that the universe began as a primal atom, an incredibly dense egg containing all the material for the universe within a sphere about 30 times larger than our Sun. This primal atom rapidly expanded for c. 10-20 G scattering matter and energy in all directions (354; 795; 850; 851). This theory is now known popularly as the Big Bang Theory, a phrase coined by Fred Hoyle (GB) in a moment of facetiousness, during a radio broadcast (710).

Alexander Friedmann (RU) proposed an expanding universe as early as 1922 (150). Note: Today, most physicists and cosmologists conceive of the primal atom as having been smaller than Lemaitre's!


On February 12, 2003, Charles L. Bennett (US) and a team from the National Aeronautics and Space administration (NASA) and the Goddard Space Flight Center in Maryland announced that the age of the universe is 13.7 G with a one percent margin for error (290; 359).


Eleanor Margaret Burbidge (US), Geoffrey R. Burbidge (US), William A. Fowler (US), and Fred Hoyle (GB) suggested that the heavier elements are formed in supernova explosions (259).

Lawrence Hugh Aller (US) concluded that nucleosyntheses in stellar interiors generates carbon, nitrogen, oxygen, phosphorus, and other biogenic elements (50).


c. 5 G

Anaxagoras of Clazomene (GR), in c. 460 B.C.E., was the first to teach that all heavenly bodies were brought into existence by the same processes that formed the earth and that all these objects are made of the same materials (61).


René Descartes (FR), in 1644, proposed the Nebular Hypothesis. It states that the solar system formed because, "God sent adrift a number of ‘vortices’ of swirling gas, and these eventually made the stars, which later changed themselves into comets, which in turn still later formed themselves into planets" (441).


Thomas Chowder Chamberlin (US) and Forest Ray Moulton (US) developed the Chamberlin-Moulton planetesimal hypothesis to explain the origin of the Earth and other planetary bodies. In contrast to the nebular-gas-cloud theory this theory held that Earth formed by accretion of small, cold bodies (dust and asteroids) (296; 984).


David J. Stevenson (US), Takafumi Matsui (JP), and Yutaka Abe (JP) reasoned that the Earth with its metallic core, highly convective mantle, molten surface, and massive steam atmosphere, formed as a direct result of accretion (13; 937; 1299).

Immanuel Kant (DE) had proposed much earlier that the Earth formed by condensation (759; 760).


Kevin J. Zahnle (US), James F. Kasting (US), and James B. Pollack (US) modeled the evolution of an impact-generated steam atmosphere surrounding an accreting Earth (1495).


c. 4.55 G

Clair Cameron Patterson (US), George Tilton (US), and Mark Ingham (US) used uranium decay in rocks from Earth and in meteorites that struck Earth to date our solar system at 4.55 G (1065-1067).


c. 4.4-3.9 G

Samuel A. Bowring (US) and Ian S. Williams (US) identified the oldest rocks found on Earth as granite-like rocks called gneiss from the Acasta Gneiss Complex near Great Slave Lake, Northwest Territory, Canada. Their age was determined to be 4.03 G. The Isua Supracrustal rocks in West Greenland are a close second at 3.7 to 3.8 G. These rocks were dated using the uranium 235 to lead 207 method (214).


Alessandro Morbidelli (IT), John Chambers (US), Jonathan I. Lunine (US), Jean-Marc Petit (IT), Francois Robert (FR), Giovanni B. Valsecchi (IT), and Kim E. Cyr (US) proposed that as the solar system formed, Jupiter's powerful gravity perturbed asteroids to accrete into larger and larger objects resulting in terrestrial "embryos" near the size of Mars. These "embryos were tossed into very unstable elliptical orbits with the result that some collided with Earth thereby delivering the water that now fills Earth's oceans. These events occurred when Earth was about half its present size (973).


Alexander Ivanovich Oparin (RU) postulated that a long chemical evolution in the oceans preceded the appearance of life on Earth (1015-1017).

John Burdon Sanderson Haldane (GB-IN), Harold Clayton Urey (US) and John Desmond Bernal (GB) also forwarded the same hypothesis (172; 625; 1369). This is often called the heterotroph hypothesis of the origin of life.


Preston Ercelle Cloud, Jr. (US) and Stanley Lloyd Miller (US) made the argument that the Earth’s primitive atmosphere was virtually devoid of oxygen (323; 964).


Kenneth M. Towe (US) made a compelling case that the Earth’s early atmosphere contained significant quantities of oxygen (1359).


John Desmond Bernal (GB), Peter C. Sylvester-Bradley (GB), S. Ichtiaque Rasool (US), Donald M. Hunten (US), William M. Kaula (US), Egon T. Degens (DE), Kenneth M. Towe (US), Edward Anders (US), Gustaf Olaf Arrhenius (SE-US), Bibhas Ranjan De (US), Hannes Olof Gosta Alfvén (SE-US), Anne Benlow (GB), Arthur Jack Meadows (GB), Manfred A. Lange (DE), and Thomas J. Ahrens (US) proposed that on the primitive Earth, impact accretions from extraterrestrial objects represented a significant source of atmospheric and biogenic elements (62; 92; 162; 173; 434; 820; 1123; 1317; 1358).


James F. Kasting (US), James B. Pollack (US), and David Crisp (US) concluded that to keep the oceans from freezing on the primitive Earth a global "greenhouse" was necessary. This "greenhouse" would have offset the effects of a faint young Sun which was dimmer than today's by 25-30%. Climate models confirm that 100-1,000 times the present atmospheric level of carbon dioxide would have been necessary to produce the ancient "greenhouse" effect (767).


Arvid Gustaf Högbom (SE) suggested that Earth's primitive atmosphere resulted from gradual, episodic, or rapid volcanic out-gassing and weathering (688).

Steffen L. Thomsen (DE), Claude J. Allègre (FR), Thomas Staudacher (FR), and Philippe Sarda (FR) determined that early catastrophic out-gassing occurred on the young Earth (49; 1349). Note: This would have released significant amounts of nitrogen, carbon dioxide, carbon monoxide, methane, water, hydrogen, sulfur dioxide, and hydrogen sulfide.


James C.G. Walker (US) and Peter Brimblecombe (GB) found that abundant aqueous ferrous iron occurring in an oceanic hydrothermal system resulted in the precipitation of otherwise highly insoluble iron sulfides. This suggests that on the primitive Earth such a system would have served as a highly effective sink for hydrogen sulfide (1423).


Bernard J. Wood (GB) and David Virgo (US) presented evidence that Earth's primitive atmosphere was poised at a redox state buffered close to the fayalite-quartz-magnetite system, which is consistent with a neutral redox atmosphere and characteristic of basalts throughout the geological record (1480).


James F. Kasting (US), Donald R. Lowe (US), and John P. Grotzinger (US) used greenhouse calculations and the sedimentary record to suggest that prior to 3.8 G the Earth’s surface was a warm (80-100˚C), with a bicarbonate-rich ocean at a pH perhaps as low as 6 (613; 767; 878).


Juan Oró (ES-US), Aubrey P. Kimball (US), Richard Reed Fritz (US), and Fenil Master (US) synthesized amino acids from formaldehyde and hydroxylamine under primitive Earth conditions (1022).


Juan Oró (US), E. Stephen-Sherwood (US), and Aubrey P. Kimball (US) synthesized adenine, thymine, amino acids, and other biochemical compounds from HCN in a primitive Earth environment (1020; 1021; 1296).


David W. Deamer (US) and Richard M. Pashley (AU) found membrane-forming non-polar molecules within the Murchison carbonaceous chondritic meteorite (432).


Keith A. Kvenvolden (US), James G. Lawless (US), Katherine Pering (US), Etta Peterson (US), Jose Flores (US), Cyril Ponnamperuma (LK-US), Isaac R. Kaplan (US), Carleton Moore (US) and John R. Cronin (US) examined the Murchison carbonaceous chondritic meteorite and found racemic mixtures of 74 different amino acids: Eight that are present in proteins, eleven with other biological roles (including, quite surprisingly, some neurotransmitters), and fifty-five that have been found almost exclusively in extraterrestrial samples (365; 810; 811).


Joan Oró (US), E. Stephen-Sherwood (US), Joseph Eichberg (US), and Dennis E. Epps (US) reported the synthesis of phospholipids under primitive Earth conditions (1023).


Joseph P. Pinto (US), G. Randall Gladstone (US), Yuk Ling Yung (US), Akiva Bar-Nun (IL), Sherwood Chang (US), and James F. Kasting (US) showed that photochemistry in an atmosphere containing carbon dioxide or a mixture of carbon monoxide and carbon dioxide yielded formaldehyde as a major product (123; 766; 1081).


Stanley Lloyd Miller (US), in Harold Clayton Urey’s (US) laboratory, showed that a wet mixture of methane, hydrogen, and ammonia exposed to electrical discharge for a while, formed traces of organic compounds, including organic acids and amino-acids regarded as exclusive components of living things (963).


William S. Brinigar (US), David B. Knaff (US), and Jui H. Wang (US) mixed a porphyrin, AMP, and inorganic phosphate with an imidazole group as a catalyst. Exposure of the mixture to ultraviolet or visible light resulted in the direct synthesis of ATP (229).


Christopher Reid (GB), Leslie Eleazer Orgel (GB-US), and Cyril Ponnamperuma (LK-US) have shown that random processes can form nucleotides and dinucleotides. They have also demonstrated the formation of ATP through the ultimate agency of solar energy (1137).


William R. Hargreaves (US), Sean J. Mulvihill (US), and David W. Deamer (US) found that fatty acids and glycerol combine spontaneously to produce phospholipids when heated to dryness at 65°C, as they might have been in an evaporating tide pool along a primitive sea (634).


John Desmond Bernal (GB) proposed that one way in which organic subunits may spontaneously combine into larger molecules is by adsorption of the reacting molecules onto the highly ordered negatively charged aluminosilicates of clays. The clay surface performs a catalytic function (171; 172).

Alexander Graham Cairns-Smith (GB), P. Ingram (GB), and Gregory L. Walker (GB) also proposed that under primitive Earth conditions organic polymers could have condensed on extremely thin layers of negatively charged aluminosilicates separated by layers of water (263).


Sidney Walter Fox (US), Kaoru Harada (JP), and Allen Vegotsky (US) showed how amino acids can be heated under Earth conditions to form proteinoids or "thermal proteins," which when placed in water self-organize into microspheres or protocells, possible precursors of the contemporary living cell (533-536).


Noam Lahav (IL), David White (US), and Sherwood Chang (US) experimentally produced peptide bonds under conditions where clay, water, and amino acids were subjected to cyclic variations in temperature and water content (814).


James R. Hawker, Jr. (US) and Juan Oró (US) synthesized peptides under plausible primitive Earth conditions (646).


E. Stephen-Sherwood (US), A. Joshi (US), and Juan Oró (US) produced polynucleotide polymers under primitive Earth conditions (1295).


A. Mar (US), Jason P. Dworkin (US) and Juan Oró (US) synthesized uridine diphosphate glucose, cytidine diphosphate choline, other phosphorylated metabolic intermediates, the coenzymes adenosine diphosphate glucose (adPG), guanosine diphosphate glucose (GDPG), and cytidine diphosphoethanolamine (CDP-ethanolamine) under primitive Earth conditions (914; 915).


Carl R. Woese (US), Francis Harry Compton Crick (GB), and Leslie Eleazer Orgel (GB-US) suggested that it would have been possible in a pre-DNA world to have a primitive replicating and catalytic apparatus devoid of both DNA and proteins and based solely on RNA molecules, i.e., an RNA world (362; 1018; 1474).

Jennifer A. Doudna (US) and Jack W. Szostak (US) found that the Tetrahymena ribozyme could splice together multiple oligonucleotides aligned on a template strand to yield a fully complementary product strand. This reaction demonstrates the feasibility of RNA-catalyzed RNA replications and supports the RNA world hypothesis (460).


Bruce Michael Alberts (US), Walter Gilbert (US), and Antonio Lazcano (MX) proposed that DNA and proteins were derived from RNA-based cells or cell-like units (36; 583; 823).


Antonio Lazcano (MX) postulated that DNA evolved to replace RNA as the repository of hereditary information because, 1) DNA is much more resistant to harsh environmental conditions, 2) DNA is less prone to mutations which cannot be repaired, 3) cytosines in DNA are not as prone to spontaneously deaminate to uracil as they are in RNA, and 4) the duplex nature of DNA offered redundancy, which when coupled with repair mechanisms had a distinct advantage over simplex RNA without a repair mechanism (824).


Carl R. Woese (US) originally described the progenote as the last common ancestor for archaebacteria (Archaea), eubacteria (Bacteria), and eukaryotes (Eucarya). It contained informational polymers, could synthesize polypeptides, and was still evolving a link between genotype and phenotype (1475; 1476).


Francis Harry Compton Crick (GB), Sydney Brenner (ZA-GB), Aaron Klug (ZA-GB), and George Pieczenik (US) proposed that the assignment of codons to particular amino acids was simply an historical accident, there being no special reasons why a particular codon stands for a given amino acid (363).


J. William Schopf (US), John M. Hayes (US), and Malcolm R. Walter (US), speculated that life on Earth might have arisen as early as 3.9 G (1215).


Norman Harold Horowitz (US) and Jerry S. Hubbard (US) proposed how complex sequential metabolic pathways may have arisen as the result of selective pressure. The retrograde model.

Suppose that a contemporary cellular pathway makes a required substance such as an amino acid through the sequence A to B to C to D to E, in which A is a simple inorganic substance and E is the final organic product. Initially E was plentiful in the environment and was absorbed directly by primitive aggregates. Later, as E became scarce because of use, chemical selection favored pre-cells that could make E from D, a slightly less complex organic substance still found in abundance in the environment. As D became exhausted, selection favored assemblies that developed the pathway C to D to E, in which the even simpler substance C could be absorbed and used as raw material to make D. This process continued until the entire synthetic pathway, based on an essentially inexhaustible inorganic substance, was established (703; 704).


Karl O. Stetter (DE) concluded that the origin of life probably took place under conditions of high temperature because the hyperthermophiles are grouped around and occupy all the deepest branches of the three-kingdom phylogenetic scheme. He also concluded that an anaerobic hyperthermophilic autotroph was very likely the original cell type (1297).


Günter Wächtershäuser (DE) presented a hypothesis supporting chemoautotrophy as the first form of metabolism to appear within life forms on the primitive Earth. He argued that these life forms were coatings that adhered to the positively charged surfaces of pyrite, a mineral composed of iron and sulfur. The formation of pyrite from hydrogen sulfide provides a source of electrons as an energy source (1414).


c. 3.5 G

J. William Schopf (US) found rock bearing 3.5-billion-year-old microfossils in the Onverwacht formation in South Africa (1211). The microfossils were interpreted to be prokaryotes (1212; 1216).


Mark E. Barley (AU), John S.R. Dunlop (AU), Joseph John Edmund Glover (AU), David I. Groves (AU), and Roger Buick (AU) concluded from their studies of sedimentary rocks in Western Australia that near 3.5 G there existed a shallow marine environment dominated by episodic island volcanism and hydrothermal activity (129; 616).


Stanley M. Awramik (US), J. William Schopf (US), Malcolm R. Walter (US), and Bonnie M. Packer (US) found rock bearing 3.5 G microfossils within early Archean (Gk. archaios=ancient) stromatolites (106; 1213; 1217). The microfossils were interpreted to be prokaryotes and to represent the oldest fossils known (1216).

Brian W. Logan (AU), Richard Rezak (US), and Robert N. Ginsburg (US) discovered living cryptozoon and associate stromatolites at Shark Bay, Western Australia (871; 872; 1090; 1091).


Harald Furnes (NO), Neil R. Banerjee (CA), Karlis Muehlenbachs (CA), Hubert Staudigel (US), and Maarten De Wit (NL) found tiny holes in volcanic glass. They believe microorganisms etched these tiny holes, c. 3.5 G (552).


Norman Richard Pace, Jr. (US) indicated that the Archaea and Bacteria diverged from one another near the time that life arose on Earth. This changed the notion of evolutionary unity among prokaryotes. The phylogenetic data support the very early appearance of the eukaryotic nuclear line of descent. The Eucarya is as old as the prokaryotic lines Archaea and Bacteria. The idea that eukaryotes resulted from the fusion of two prokaryotes and are late arrivals on the evolutionary stage (1-1.5 G) is incorrect (1036).


Carl R. Woese (US) proposed that the halophilic archaebacteria (Archaea) are a group of aerobic or microaerophilic organisms that evolved from a strictly anaerobic and nonhalophilic methanogen ancestor. Woese also constructed a trifurcated, unrooted, universal evolutionary tree in which all known organisms can be grouped in one of three major lineages: eubacteria (Bacteria), the archaebacteria (Archaea), and the eukaryotic (Eucarya) nucleocytoplasm. This is often referred to simply as the three-kingdom scheme (1476).


Mitchell Lloyd Sogin (US), John H. Gunderson (US), Hillie J. Elwood (US), Rogelio A. Alonso (US), and Debra A. Peattie (US) determined that the 16S-like rRNA of the diplomonad Giardia lamblia has retained many of the features that may have been present in the common ancestor of eukaryotes (Eucarya) and prokaryotes (Archaea or Bacteria). They concluded that it represents the earliest-branching eukaryotic lineage (1278).


Mitchell Lloyd Sogin (US) declared that some microbial lineages seem never to have had mitochondria and chloroplasts, so may have diverged from the eukaryotic (Eucarya) line of descent prior to the incorporation of the organelles (1277).


c. 3.235 G

Birger Rasmussen (AU) discovered pyritic filaments, the probable fossil remains of thread-like microorganisms, in a 3,235-million-year-old deep-sea volcanogenic massive sulfide deposit from the Pilbara Craton of Australia (1122). Note: From their mode of occurrence, the microorganisms were probably thermophilic chemotropic prokaryotes, which inhabited sub-sea-floor hydrothermal environments. They represent the first fossil evidence for microbial life in a Precambrian submarine thermal spring system and extend the known range of submarine hydrothermal biota by more than 2,700 million years. Such environments may have hosted the first living systems on Earth, consistent with proposals for a thermophilic origin of life. See, Corliss, 1981.


c. 2.7 G

Roger E. Summons (AU), Linda L. Jahnke (AU), Janet M. Hope (AU), Graham A. Logan (AU), Jochen J. Brocks (AU), and Roger Buick (AU) found molecular fossils of biological lipids preserved in 2,700-million-year-old shales from the Pilbara Craton, Australia. This makes these the oldest known biomolecules. The presence of abundant 2 alpha-methylhopanes, which are characteristic of cyanobacteria, indicates that oxygenic photosynthesis evolved well before the atmosphere became oxidizing. The presence of steranes, particularly cholestane and its 28- to 30-carbon analogs, provides persuasive evidence for the existence of eukaryotes 500 million to 1 billion years before the extant fossil record indicates that the lineage arose (231; 1310).


c. 2.5 G

The Proterozoic Era (Gk. proteros=early; zoe=life) extended from 2.5 G to 544 Ma. It is considered to represent the most recent Era of the Precambrian Time.


c. 2.1 G

Preston Ercelle Cloud, Jr. (US) proposed a working model of the primitive Earth in which he related atmospheric-geologic-biologic history of the Precambrian (322).


Stanley A. Tyler (US) and Elso Sterrenberg Barghoorn (US) reported the discovery of fossil microscopic organisms in an outcropping of mid-Precambrian rocks called the Gunflint Iron formation near Lake Superior in Ontario. Most of these fossils resemble present day bacteria and cyanobacteria. This was the first indisputable evidence of Precambrian life (1366). Barghoorn, Tyler, and Preston Ercelle Cloud, Jr. (US) later confirmed these findings and discussed their significance (127; 321). Note: Other Precambriam fossil sites include: the Fig Tree Group, Africa; the Bulawayan Formation, Africa; the Gunflint Iron Formation, Minnesota/Canada; the Belcher Group, Hudson Bay; Bitter Springs, Australia; and the Ediacaran Sites, Australia.


Tsu-Ming Han (US) and Bruce N. Runnegar (AU-US) found fossils of the multi-cellular Grypania spiralis (probably an alga) in the 2.1 G Negaunee Iron Formation in Michigan, U.S.A. (632).

Malcom R. Walter (US), Du Rulin (US), and Robert Joseph Horodyski (US) had previously discovered multi-cellular fossils (c.1.4 G) in old Greyson Shale, lower Belt Supergroup, in Montana, US, and from the similarly aged Gaoyuzhuang Formation, upper Changcheng Group, in the Jixian section, Northern China. The organism was identified as Grypania spiralis, a coiled ribbon-like creature. It was judged to most likely have been a multi-cellular eukaryotic alga (1427). Shale is rock formed by condensation of layers of clay or mud, along with phytoplankton and other debris, deposited at the bottoms of lakes or ocean basins.


Konstantin Sergejewitsch Mereschkowsky (RU) proposed the theory of the symbiotic origin of the eukaryotic cell and introduced the term symbiogenesis to signify the emergence of new species with identifiably new physiologies and structures as a consequence of stable integration of symbionts. It stated that the chloroplast and mitochondria of eukaryotic cells had their origins from endosymbiotic cyanobacteria and aerobic bacteria, respectively, whose ancestors were once captured and incorporated by a primitive, anaerobic, heterotrophic host. Many others would later refine this theory (284; 285; 783; 784; 917; 956).


c. 2 G

J. William Schopf (US) Elso Sterrenberg Barghoorn (US), Morton D. Maser (US), and Robert O. Gordon (US) found microscopic formations that looked very much like traces of cyanobacteria in 2-billion-year-old rock called Gunflint chert. The find was near Lake Superior in Canada (1214). Cherts are rocks composed of minute interlocking grains of silica, occurring as the mineral quartz (SiO2).

Elso Sterrenberg Barghoorn (US) and J. William Schopf (US) discovered fossils of microorganisms in stromatolitic cherts of the Neoproterozoic Bitter Springs Formation of the Amadeus Basin of Central Australia (126; 1210).

Other Precambrian fossil sites include: the Fig Tree Group, Africa; the Bulawayan Formation, Africa; the Gunflint Iron Formation, Minnesota/Canada; the Belcher Group, Hudson Bay; Bitter Springs, Australia; and the Ediacaran Sites, Australia.


c. 1.8 G- 600 M (mega annum = million years)

Zh Zhang (CN) discovered large (40-200 micrometer) spherical microfossils 1.8 to 1.9 billion years old in sedimentary rocks from China. These microfossils were interpreted to be the earliest known eukaryotes (Eucarya) (1499).


c. 1.4 G

Malcolm R. Walter (US), Du Rulin (US), and Robert Joseph Horodyski (US) discovered the oldest known multicellular fossils. They were removed from 1400 M Old Greyson Shale, Lower Belt Supergroup, in Montana, US, and from the similarly aged Gaoyuzhuang Formation, Upper Changcheng Group, in the Jixian Section, Northern China. The organism was identified as Grypania spiralis, a coiled ribbon-like creature. It was judged to most likely have been a multicellular eukaryotic alga (1427). Note: Shale is rock formed by condensation of layers of clay or mud sediment, along with phytoplankton and other debris, at the bottoms of lakes or ocean basins.


c. 1 G

The ultraviolet absorbing ozone layer in Earth's atmosphere began to appear. High in the atmosphere, some oxygen (O2) molecules absorbed energy from the Sun's ultraviolet rays and split to form single oxygen atoms. These atoms combined with remaining oxygen (O2) to form ozone (O3) molecules, which are very effective at absorbing UV rays. Most microorganisms had already evolved ways to protect themselves from ultraviolet radiation, e.g. DNA repair systems, ultraviolet absorbing pigments, and outer skeletons (1363).


Joseph Felsenstein (US) created evolutionary trees using rRNA sequences and a maximum likelihood approach. He concluded that the Plantae, Animalia, and Fungi along with two new evolutionary assemblages (alveolates and stramenophiles) diverged nearly simultaneously (509). Alveolates include dinoflagellates, apicomplexans, and ciliated protozoans. The stramenopiles include brown algae, labyrinthulids, chrysophytes, xanthophytes, diatoms, and oomycetes (1064).


Elso Sterrenberg Barghoorn (US) and J. William Schopf (US) discovered fossils of microorganisms in stromatolitic cherts of the Neoproterozoic Bitter Springs Formation of the Amadeus Basin of central Australia (126; 1210). Cherts are rocks composed of minute interlocking grains of silica, occurring as the mineral quartz (SiO2).

Other Precambrian fossil sites include: the Fig Tree Group, Africa; the Bulawayan Formation, Africa; the Gunflint Iron Formation, Minnesota/Canada; the Belcher Group, Hudson Bay; Bitter Springs, Australia; and the Ediacaran Sites, Australia.


Gerard Peter Kuiper (NL-US) proposed that the Earth’s early atmosphere was rich in hydrogen and helium most of which would drift into space over the next 1 billion years and be replaced by a secondary atmosphere rich in heavier gases (806).


c. 700 M (mega-annum = million years)

Paul F. Hoffman (US), Alan J. Kaufman (US), Galen P. Halverson (US), and Daniel P. Schrag (US) theorized that the explosion of life-forms in the Cambrian resulted following extended glaciation during which the entire Earth was covered thus killing most life forms. Volcanic eruptions then released enough carbon dioxide to warm the Earth creating vast shallow seas in which rapid evolution occurred. They called it neoproterozoic snowball Earth (684; 685).


J. William Schopf (US), Bonnie M. Packer (US), Roger Buick (AU), and Stanley M. Awramik (US) presented evidence for a well-established community of oxygenic photosynthesizers (105; 255; 1217).


Charles Doolittle Walcott (US) identified pillar shaped masses of thinly layered limestone rock in Precambrian strata from the Grand Canyon in Western North America. Although he did not understand their significance as fossils he later interpreted these pillar like structures of limestone as fossilized reefs laid down by algae (cyanobacteria) (1416). These pillar-like structures called cryptozoon (hidden life) are now called stromatolites.


Charles Doolittle Walcott (US) described an important clue in the search for Precambrian life when he discovered fossils in Precambrian carbon-rich shales on the slopes of a prominent butte deep within the Grand Canyon. The shales belonged to what is known as the Chuar Group of strata, so, Walcott named the fossils Chuaria. Chuaria is now known to be an unusually large, originally spheroidal, single-celled planktonic alga, i.e., a megasphaeromorph acritarch. Walcott's specimens were indeed authentic fossils, the first true Precambrian organisms where cellular detail is recorded (1417).


c. 635 M

Roger Mason (GB) Tina Negus (GB) and other school children discovered in Charnwood Forest, England the Precambrian fossil remains of what may very well be the oldest known multicellular animal (later named Charnia). Trevor D. Ford (GB) reported this discovery. The position of the clade for this organism in the tree of life remains uncertain (530).

Jonathan B. Antcliffe (GB) and Martin D. Brasier (GB) note that Charnia is both temporally and geographically the most widespread Ediacaran fossil (69).

Guy M. Narbonne (CA) and James G. Gehling (AU) report that the greatest abundance of specimens of Charnia, which are also the oldest reliably dated Ediacaran fossils, are found along the southeast coast of Newfoundland (991). Note: Other Precambrian fossil sites include: the Fig Tree Group, Africa; the Bulawayan Formation, Africa; the Gunflint Iron Formation, Minnesota/Canada; the Belcher Group, Hudson Bay; Bitter Springs, Australia; and the Ediacaran Sites, Australia.


c. 600 M

Reginald Claude Sprigg (AU) discovered Precambrian metazoan fossils in the Pound Quartzite at Ediacara Hills and in the Flinders Ranges of South Australia. At the time of discovery, he thought these fossils were from the Cambrian (1286; 1287).


Ilya Bobrovskiy (AU), Janet M. Hope (AU), Andrey Ivantsov (RU), Benjamin J. Nettersheim (DE), Christian Hallmann (DE), Jochen J. Brooks (AU) used lipid biomarkers obtained from Dickinsonia fossils and found that the fossils contained almost exclusively cholesteroids, a marker found only in animals. Thus, Dickinsonia were basal animals. This supports the idea that the Ediacaran biota may have been a precursor to the explosion of animal forms later observed in the Cambrian, about 500 million years ago (192).


Martin Fritz Glaessner (CZ-AU) and Mary Wade (AU) determined fossils in the Ediacara Hills of South Australia (Ediacaran fauna) to be late Precambrian in age, making them the oldest-known multi-celled organisms (586-589).


Mary L. Droser (US) and James G. Gehling (AU) believe they have found the earliest fossil evidence for sexual reproduction in Funisia, an Ediacaran "animal". Its relationship to other animals is unknown (461).


c. 590-550 M

The Cambrian Period of the Paleozoic Era extended from 590 M to 505 M.

The word Cambrian is taken from Cambria, the Latin name for modern Wales. Other fossil rich Cambrian sites include: Chengjiang, China; the Wheeler Formation in Utah; and the Croixan Series in Minnesota/Wisconsin.

With one exception (the phylum Bryozoa), every metazoan phylum with hard parts, and many that lack hard parts, made their first appearances in the Cambrian. However, Cambrian marine life was quite different from modern biotas; the dominant invertebrates with hard parts were trilobites, inarticulate brachiopods, archaeocyathids, and problematic conical fossils known as hyolithids. Many Early Cambrian invertebrates are known only from small shelly fossils - tiny plates and scales and spines and tubes and so on, many of which were pieces of the skeletons of larger animals (1225). Note: This publication initiated the early Paleozoic time scale. Many Cambrian fossils are found in shale (a rock formed by condensation of layers of clay or mud, along with phytoplankton and other debris, deposited at the bottoms of lakes or ocean basins).


c. 544 M

The Phanerozoic Eon (Gk. phaneros=visible; zoe=life) extends from 544 M to the present. It contains three eras, the Paleozoic, the Mesozoic, and the Cenozoic.


c. 541 M

Alexandr Petrovich Karpinsky (RU) recorded his classic work on Paleozoic fossil sharks of the family Edestidae (763; 765).


c. 513 M

Charles Doolittle Walcott (US), in 1909, discovered a rich assemblage of algae and invertebrate fossils from the Middle Cambrian Period of the Paleozoic Era in the Burgess shale located in Yoho National Park in the Rocky Mountains, near Field, British Columbia, Canada (1418). Note: The word Cambrian is taken from a Latin form of the Welsh name for Wales. Other fossil rich Cambrian sites include Chengjiang, China, the Wheeler Formation in Utah, and the Croixan Series in Minnesota-Wisconsin. (Shale is rock formed by condensation of layers of clay or mud, along with phytoplankton and other debris, sedimented at the bottoms of lakes or ocean basins.)


Harry Blackmore Whittington (GB), in 1966, began re-examining Burgess Shale fossils originally identified by Charles Doolittle Walcott (US) as early as 1909. Over the next two decades, Whittington, with the assistance of his graduate students Simon Conway-Morris (GB) and Derek Briggs (GB), eventually overturned Walcott's theories that these organisms all belonged to modern phyla and proposed that most of the specimens are much more complex than originally believed, and have left no living relatives (347; 1450; 1451).


c. 505 M

Charles Lapworth (GB), from his extensive analysis of graptolite fossils in Scotland, proposed the Ordovician System of strata to resolve the Murchison-Sedgwick conflict over their overlapping claims for their Silurain and Cambrian systems (822). The Ordovician (from the name of an ancient British tribe, the Ordovices) Period of the Paleozoic Era extended from 505 M until 438 M. At the end of the Cambrian, sea levels fell, causing extinctions. It was in the Ordovician that the first animals with backbones arose, the Agnatha, these jawless fishes were the first animals with true bony skeletons. The Ordovician is best known for the presence of its diverse marine invertebrates, including, corals, graptolites, trilobites, brachiopods, and the conodonts (early vertebrates). A typical marine community consisted of these animals, plus red and green algae, primitive fish, cephalopods, corals, crinoids, and gastropods. More recently, there has been found evidence of tetrahedral spores that are like those of primitive land plants, suggesting that plants invaded the land at this time.

Paul Kendrick (US) and Peter R. Crane (US) reasoned that the actual colonization of land by plants could have begun during the Early Cambrian, considering that the appearance of dispersed plant spores predated the first land plant megafossils by c. 50 million years (776).


The Ordovician Period ended with a mass extinction. About 25% of all families did not make it into the Silurian.

Classic fossil-bearing rocks of the Ordovician Period include: Whiterock Formation, Utah; and the Nevada Cincinnatian Series, Ohio/Indiana/ Kentucky.


c. 466 M

Jane Gray (US), Wilson N. Stewart (US), and Gar W. Rothwell (US) suggest that the first major adaptive radiation by plants onto land occurred in the mid Ordovician (466 M). These early plants are represented by abundant obligate spore tetrads; this assemblage persisted from the mid Ordovician to about the mid-late Early Silurian (429.5-416 M). The close similarity of the fossil tetrads with obligate spore tetrads produced by some hepatics and mosses suggests a non-vascular vegetative grade of organization for plants of this interval. During this period most land was collected into the southern supercontinent Gondwana (608; 1301).


Jonathan P. Rast (CA) and Katherine M. Buckley (CA) showed that differences between the immune response of humans and their ancestors only become apparent when comparing humans with jawless fish (lampreys and hagfish; the last common ancestor with humans lived 460 million years ago). Jawless fish use a more primitive immune system which, nevertheless, already consists of variable lymphocyte receptors (1124).


Peter R. Sheldon (GB) collected 15,000 trilobite specimens from the Ordivician stratum around Builth Wells, England. Their fossilized remains make a strong case for gradual evolutionary change (1255).


444-359 M

Thomas Chrowder Chamberlain (US) was the first to suggest a continental freshwater origin of vertebrates during the Silurian and Devonian time (294). Currently most scholars support a marine origin for vertebrates.


c. 439 M

Roderick Impey Murchison (GB) defined and named the Silurian Period commemorating the Silures, an ancient tribe that had inhabited the type area in the Welsh borderland region (987). The Silurian Period of the Paleozoic Era lies between approximately 438 M and 408 M. No new major groups of organisms appeared at this time, with old groups flourishing or declining. It is at this time that our first good evidence of life on land is preserved, including the earliest fossils of vascular plants and relatives of spiders and centipedes. The insects arose in the Silurian, probably becoming the first animal forms to venture out of the water. Increased ozone from photosynthetic water plants provided protection from ultraviolet rays, making the terrestrial environment hospitable to those organisms that could prevent desiccation. Coral reefs made their first appearance during this time, and the Silurian was also a remarkable time in the evolution of fishes. Not only does this period mark the wide and rapid spread of jawless fish, but also the highly significant appearances of both the first known freshwater fish as well as the first fish with jaws.

Classic Fossil-Bearing rocks of the Silurian Period include: Wadi Ram in Jordon; Brandon Bridge in Wisconsin; and the Brownsport Group in Tennessee.


Martha Allen Sherwood-Pike (US) and Jane Gray (US) reported finding fossil evidence of fungi (Ascoymcota) in material from the Silurian period (438-408 M) (1258).


Errol Ivor White (GB) discovered a fossil of Jamoytius kerwoodi in deposits of Silurian rock in Scotland. It is probably the most primitive chordate known and may throw some light on the early ancestry of vertebrates (1447).


c. 429.5 M

Jan Gray (US) decided that the interval from the mid-late Early Silurian (429.5-416 M) to the Pridoli (423 ± 2.3 and 419.2 ± 3.2 M) largely coincides with the appearance of vascular plant megafossils. It is hypothesized on the basis of the spore assemblages that this interval is one of major establishment of large populations of genetically diverse plants exploiting a broad spectrum of ecological sites (608).


Wout Boerjan (BE), John Ralph (BE), and Marie Baucher (BE) presented a current picture of monolignol biosynthesis, polymerization, and lignin structure. They noted that it was not until the rise of tracheophytes, which had developed the ability to deposit the phenylpropanoid polymer lignin in their cell wall, that land plants truly flourished and began their dominance of the terrestrial ecosystem. Lignin bestowed the early tracheophytes with the physical rigidity to stand upright, strengthened the water-conducting cells for long-distance water transport, and allowed plants to expand significantly in body size compared with their sister group, the bryophytes. The nature and randomness of the linkages in lignin also made lignin one of the most difficult biopolymers to degrade, an ideal characteristic for a defensive barrier against the pathogens and herbivores that would soon co-evolve with vascular plants (196).


c. 420 M

Dianne Edwards (GB) and E. Catherine W. Rogerson (GB) discovered Cooksonia pertonii near Brecon Beacons, England in 420 M rock (475; 476). William H. Lang (GB) had earlier positioned it as the earliest known land-living vascular plant found in England and one of the earliest in the world (818).


c. 414 M

Leif Størmer (NO) reported that arthropods likely invaded the land during late Silurian and early Devonian times (1305; 1306).


c. 408 M

Adam Sedgwick (GB) and Roderick Impey Murchison (GB) presented researches on certain rocks in Devonshire, England, which had a distinctive fossil assemblage that led them to propose a new division of the geological time scale—the Devonian. They first used Devonian in a publication (1226). Note: This represents the discovery of the Devonian Period—408 M to 360 M—of the Paleozoic Era.

William Lonsdale (GB), in 1837, suggested from a study of the fossils of the South Devon limestones that they would prove to be of an age intermediate between the Carboniferous and Silurian systems. It was Lonsdale who coined the term Devonian, commemorating Devon County, England (876).


The Devonian seas were dominated by brachiopods, such as the spiriferids, and by tabulate and rugose corals, which built large bioherms, or reefs, in shallow waters. Encrusting red algae also contributed to reef building. In the Lower Devonian, ammonoids appeared, leaving us large limestone deposits from their shells. Bivalves, crinoid and blastoid echinoderms, graptolites, and trilobites were all present, though most groups of trilobites disappeared by the close of the Devonian. The Devonian is also notable for the rapid diversification in fish. Benthic armored fish are common by the Early Devonian. These early fish are collectively called ostracoderms and include a number of different groups. By the Mid-Devonian, placoderms, the first jawed fish, appear. Many of these grew to large sizes and were fearsome predators. Of the greatest interest to us is the rise of the first sarcopterygiians, i.e., the lobe-finned fish, which eventually produced the first tetrapods just before the end of the Devonian. By the Devonian Period, life was well underway in its colonization of the land. Before this time, there is no organic accumulation in the soils, causing these soil deposits to be a reddish color. This is indicative of the underdeveloped landscape, probably colonized only by bacterial and algal mats. By the start of the Devonian, however, early terrestrial vegetation had begun to spread. These plants did not have roots or leaves like the plants most common today, and many had no vascular tissue at all. They probably spread largely by vegetative growth and did not grow much more than a few centimeters tall. These plants included the now extinct zosterophylls and trimerophytes. The early fauna living among these plants were primarily arthropods: mites, trigonotarbids, wingless insects, and myriapods, though these early faunas are not well known. By the Late Devonian, lycophytes, sphenophytes, ferns, and progymnosperms had evolved. Most of these plants have true roots and leaves, and many are rather tall plants. The progymnosperm Archaeopteris was a large tree with true wood. It is the oldest such tree known and produced some of the world's first forests. This rapid appearance of so many plant groups and growth forms has been called the Devonian Explosion. Along with this diversification in terrestrial vegetation structure, came a diversification of the arthropods.

Rocks rich in Devonian fossils include: Silica Shale in Ohio; Bundenbach in Germany; Cleveland Shale in Ohio; and the Rhynie in Scotland.


Kesava Mukund Lele (GB) and John Walton (GB) reported that the earliest plant stomata appeared in Zosterophyllum myretonianum. These were more like stomata found in modern moss sporophytes. The type found in vascular plants appeared 4-5 M (849).


Tamara Anastasevna Ishchenko (RU) and R.N. Shylokov (RU) discovered fossil Marchantiales in Lower Middle Devonian material from the USSR. This provided evidence that some major bryophyte divisions were well established by the Lower Devonian and that the bryophytes in general must have played a part in the initial colonization of land by plants (732).


Alexandr Petrovich Karpinsky (RU) reported research on Devonian algae, the so-called charophytes. His study of the contemporary charophytes showed their closeness to extinct Devonian forms and indicated that they likely had a common ancestor (764; 765).


Jennifer A. Clack (GB) and Michael I. Coates (GB) reported on fossil specimens of the Devonian fish-like Acanthostega gunneri they collected during 1987 in Greenland. Their work strongly suggested that legs appeared in tetrapods well before they abandoned water and not vice-versa as had been suggested by the popular dry pond theory first articulated by Alfred Sherwood Romer (US) (314; 325-327).


Hagen Hass (DE), Thomas N. Taylor (US), Winfried Remy (PL-DE), and Hans Kerp (DE) found fossil hyphae in association with wood decay and fossil chytrids and Glomales-Endogenales representatives associated with plants of the Rhynie Chert from the Devonian Period (408-360 mya) (644; 1138; 1139; 1326; 1327). These findings strongly suggest that the ability to form an arbuscular-mycorrhizal symbiosis occurred early in the evolution of vascular plants.


Roy A. Norton (US), Patricia M. Bonamo (US), James D. Grierson (US), and William A. Shear (US) found that mites are among the oldest of all terrestrial animals, with fossils known from the early Devonian, nearly 400 M (1004).


c. 396 M

John William Dawson (CA) discovered fossil plant remains (Psilophyton princeps) in Middle and Lower Devonian rocks from the Gaspé Peninsula in Eastern Canada (382; 383).

Thore Gustaf Halle (SE), Robert Kidston (GB), and William H. Lang (GB) later found similar confirming fossils in the Rhynie Chert and established the order Psilophytes (627; 785).

Harlan Parker Banks (US) subsequently split the Psilophytes into three divisions: Rhyniophytina (Rhyniophyta), Zosterophyllophyta, and Trimerophytina (Trimerophytophyta) (122). One of the most famous Early Devonian land plant localities is Rhynie in Aberdeenshire, Scotland. The Rhynie Chert is one of the most important fossil plant occurrences because it represents the oldest and most completely preserved terrestrial ecosystem. The Rhynie Chert has been radiometrically dated at 396 mya (Pragian). Plant remains show excellent cellular preservation. Three groups of plants are represented: the Rhyniophytes, the Zosterphyllophytes and a lycopod.


c. 387 M

Tamara Anastasevna Ishchenko (RU) and R.N. Shylokov (RU) discovered fossil Marchantiales in lower Middle Devonian material from the USSR providing evidence that some major bryophyte divisions were well established by the Lower Devonian and that the bryophytes in general must have played a part in the initial colonization of land by plants (732).


Charles B. Beck (US) reported that the original arborescent plants bore a planated lateral branch system with helically arranged simple leaves very similar to those of some modern conifers (148).


c. 375 M

Edward B. Daeschler (US), Neil H. Shubin (US), and Farish A. Jenkins (US) unearthed a fossil they named "Tiktaalik" on Ellesmere Island in the Arctic region of Canada. It is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the Late Devonian Period, about 375 mya (million years ago), having many features akin to those of tetrapods (four-legged animals). It is technically a fish, complete with scales and gills - but it has the flattened head of a crocodile and unusual fins. Its fins have thin ray bones for paddling like most fish, but they also have sturdy interior bones that would have allowed "Tiktaalik" to prop itself up in shallow water and use its limbs for support as most four-legged animals do. Those fins and a suite of other characteristics set "Tiktaalik" apart as something special; it has a combination of features that show the evolutionary transition between swimming fish and their descendants, the four-legged vertebrates - a clade which includes amphibians, reptiles, birds and mammals (378). Note: The name "Tiktaalik" is an Inuktitut word meaning "large freshwater fish."


c. 360 M

The Carboniferous Period of the Paleozoic Era occurred from about 360 to 286 mya. The term carboniferous comes from England and refers to the rich deposits of coal that occur there. These deposits of coal occur throughout Northern Europe, Asia, and Midwestern and Eastern North America. William Daniel Conybeare (GB) and William Phillips (GB) named the Carboniferous Period in their Outlines of Geology of England and Wales (348). The term carboniferous is used throughout the world to describe this period, although it has been separated into the Mississippian (Lower Carboniferous, 360 mya to 323 mya) and the Pennsylvanian (Upper Carboniferous, 323 mya to 286 mya) in the United States. This separation was adopted to distinguish the coal-bearing layers of the Pennsylvanian from the mostly limestone Mississippian and is a result of differing stratigraphy on the different continents. The Pennsylvanian was named in 1858 by Henry Darwin Rogers (US), and the Mississippian named by Alexander Winchell (US) in 1870; both these divisions were given system/period status in Geology by Thomas Chrowder Chamberlin (US) and Rollin D. Salisbury (US) (296; 1155; 1468). In addition to having the ideal conditions for the beginnings of coal, several major biological, geological, and climatic events occurred during this time. One of the greatest biological evolutionary innovations of the Carboniferous was the amniote egg, which allowed for the further exploitation of the land by certain tetrapods. The amniote egg prevented the desiccation of the embryo inside thus allowing the ancestors of birds, mammals, and reptiles to reproduce on land. There was also a trend towards mild temperatures during the Carboniferous, as evidenced by the decrease in lycopods and large insects and an increase in the number of tree ferns.

Geologically, the Late Carboniferous collision of Laurussia (present-day Europe and North America) into Godwanaland (present-day Africa and South America) produced the Appalachian mountain belt of Eastern North America and the Hercynian Mountains in the United Kingdom. A further collision of Siberia and Eastern Europe created the Ural Mountains.

The stratigraphy of the Lower Carboniferous can be easily distinguished from that of the Upper Carboniferous. The environment of the Lower Carboniferous in North America was heavily marine when seas covered parts of the continents. As a result, most of the mineral found in Lower Carboniferous is limestone, which is composed of the remains of crinoids, lime-encrusted green algae, or calcium carbonate shaped by waves. The North American Upper Carboniferous environment was alternately terrestrial and marine, with the transgression and regression of the seas caused by glaciation. These environmental conditions, with the vast amount of plant material provided by the extensive coal forests allowed the production of coal. Plant material did not decay when the seas covered them. Pressure and heat built up over the millions of years to transform the plant material to coal.

Rocks rich in Carboniferous fossils include: Mazon Creek, Illinois, Joggins Formation, Nova Scotia, Edinburgh Coal Beds, Scotland, and Anthracite Coal Beds, Eastern United States.


Robert Arbuckle Berner (US) reported that organic carbon accumulated at an exceptionally high rate during the Carboniferous and Permian, resulting in the formation of vast coal deposits, derived primarily from lignin (175). Note: The sharp decline in the rate of organic carbon burial at the end of the Permo-Carboniferous was caused, at least in part, by the evolution of lignin decay capabilities in white rot Agaricomycetes .


 Andrew C. Scott (GB) and William Gilbert Chaloner (GB) provided the earliest fossil record of a gymnosperm, conifers from the Upper Carboniferous (1224).


John Walton (GB) presented evidence of mosses and liverworts from the Carboniferous deposits in England (1428).


c. 340 M

Erik Andersson Stensiö (SE) and Gunnar Säve-Söderbergh (SE), of the 1929-1930 Danish scientific expeditions, found ichthyostegid fossils in the upper Devonian sediments in Eastern Greenland. They appear to be intermediate between lobe-finned rhipidistians (Osteolepis) and early amphibians. These are the oldest known fossils that can be classified as amphibians (1195; 1294).


c. 335 M

Stan Wood (GB) discovered the 20 cm long fossilized remains of Westlothiana lizziae in East Kirkton, West Lothian, Scotland (near Edinburgh). Tim R. Smithson (GB), Robert Lynn Carroll (US-CA), Alec L. Panchen (GB), S. Mahala Andrews (GB), Roberta L. Paton (GB), and Jennifer Alice Clack (GB) clarified its taxonomic status and concluded that it might be the oldest known reptile and thus the oldest known amniote (1040; 1061; 1275; 1276).


William Martin (DE), Alfons Gierl (DE), Heinz Saedler (DE) reported molecular evidence suggesting that angiosperm ancestors underwent diversification more than 300 Myr. ago (930).

Kenneth H. Wolfe (US), Manolo Gouy (US), Yau-Wen Yang (US), Paul M. Sharp (US), and Wen-Hsiung Li (US) estimated the date of the divergence between monocots and dicots by reconstructing phylogenetic trees from chloroplast DNA sequences, using two independent approaches: The rate of synonymous nucleotide substitution was calibrated from the divergence of maize, wheat, and rice, whereas the rate of nonsynonymous substitution was calibrated from the divergence of angiosperms and bryophytes. Both methods lead to an estimate of the monocot-dicot divergence at 200 mya (with an uncertainty of about 40 mya). This estimate is also supported by analyses of the nuclear genes encoding large and small subunit ribosomal RNAs. These results imply that the angiosperm lineage emerged in Jurassic-Triassic time, which considerably predates its appearance in the fossil record (approximately 120 mya). They estimated the divergence between cycads and angiosperms to be approximately 340 mya, which can be taken as a lower boundary for the age of angiosperms (1477).


c. 286 M

The Permian Period of the Paleozoic Era (from Perm, a Russian province) lasted from 286 to 248 M. The Period was first defined by Roderick Impey Murchison (GB) (988). The distinction between the Paleozoic and the Mesozoic is made at the end of the Permian in recognition of a large mass extinction of life on Earth. It affected many groups of organisms in many different environments, but it affected marine communities the most by far, causing the extinction of most of the marine invertebrates of the time. Some groups survived the Permian mass extinction in greatly diminished numbers, but they never again reached the ecological dominance they once had, clearing the way for another group of sea life. On land, a relatively smaller extinction of diapsids and synapsids cleared the way for other forms to dominate and led to what has been called the Age of Dinosaurs. Also, the great forests of fern-like plants shifted to gymnosperms, plants with their offspring enclosed within seeds. Modern conifers, the most familiar gymnosperms of today, first appear in the fossil record of the Permian. In all, the Permian was the last of time for some organisms and a pivotal point for others, and life on earth was never the same again.

The global geography of the Permian included massive areas of land and water. By the beginning of the Permian, the motion of the Earth's crustal plates had brought much of the total land together, fused in a supercontinent known as Pangea. Many of the continents of today in somewhat intact form met in Pangea (only Asia was broken up at the time), which stretched from the northern to the southern pole. Most of the rest of the surface area of the Earth was occupied by a corresponding single ocean, known as Panthalassa, with a smaller sea to the east of Pangea known as Tethys.

Models indicate that the interior regions of this vast continent were probably dry, with great seasonal fluctuations, because of the lack of the moderating effect of nearby bodies of water, and that only portions received rainfall throughout the year. The ocean itself still has little known about it. There are indications that the climate of the Earth shifted at this time, and that glaciation decreased, as the interiors of continents became drier.

Rocks rich in Permian fossils include: Glass Mountains, Texas; Abo Formation, New Mexico; Kuperschiefer, Germany; and Glossopteris flora in Gondwana localities.

Paul R. Renne (US), Michael T. Black (US), Zhang Zichao (CN), Mark A. Richards (US), and Asish R. Basu (US) showed synchrony and causal relations between the Permian-Triassic boundary crises and Siberian flood volcanism (1141).

Paul B. Wignall (GB) and Richard J. Twitchett (GB) presented data on rocks from Spitsbergen and the equatorial sections of Italy and Slovenia indicating that the world's oceans became anoxic at both low and high paleolatitudes in the Late Permian. Such conditions may have been responsible for the mass extinction at this time. This event affected a wide range of shelf depths and extended into shallow water well above the storm wave base (1456).

Samual A. Bowring (US), Douglas H. Erwin (US), Yugan G. Jin (CN), Mark W. Martin (US), Kathleen Davidek (US), and Wei Wang (CN) reported that uranium/lead zircon data from Late Permian and Early Triassic rocks from south China place the Permian-Triassic boundary at 251.4 ± 0.3 million years ago. Biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the Changhsingian pulse of the end-Permian extinction, corresponding to the disappearance of about 85 percent of marine species, lasted less than 1 million years (213). Note: Seth D. Burgess (US), Samuel A. Bowring (US), and Shu-zhong Shen (CN) refined the date of the Permian extinction to between 251.941 ± 0.037 and 251.880 ± 0.031 Mya (260).

Svetoslav Georgiev (US), Holly J. Stein (US), Judith L. Hannah (US), and Bernard Bingen (NO), Hermann M. Weiss (NO), and Stefan Piasecki (DK) presented evidence that hot acidic Late Permian seas stifled life in record time (573).


Andrei Vasilevich Martynov (RU) discovered the oldest undoubted Coleoptera (beetles) fossils in Upper Permian deposits in North Russia (931).


Francis Wall Oliver (AU) and Dunkinfield Henry Scott (GB) discovered evidence for the seed of Lyginodendron, which led to the removal of the Cycadofilices from the Pteridophyta (ferns, horsetails, and club-mosses) and their inclusion with the gymnosperms (1011).

“We now know that the true ferns were only present in the coal measures in small and archaic forms (Coenopteridales) very unlike living ferns and most likely all the conspicuous fern-like leaves of that era belonged to seed plants” (913).


Charles H. Sternberg (US) discovered the fossil remains of a creature showing both amphibian and reptilian characteristics. Ferdinand Broili (DE) would name it Seymouria baylorensis for Seymour, Texas in Baylor County (232).

Samuel Wendell Williston (US) and Ermine Cowles Case (US) described Seymouria and other labyrinthodont amphibian and reptile fossils from the Permian beds of Texas and New Mexico (276; 1463-1465).


251.9 M

Yadong Sun (CN), Michael M. Joachimski (DE), Paul B. Wignall (GB), Chunbo Yan (CN), Yanlong Chen (AT), Haishui Jiang (CN), Lina Wang (CN), and Xulong Lai (CN) suggested that the "Siberian Traps" are the primary cause of the Permian–Triassic extinction event, the most severe extinction event in the geologic record (1312). Note: The "Siberian Traps" is a large region of volcanic rock, known as a large igneous province, in Siberia, Russia. The massive eruptive event that formed the traps is one of the largest known volcanic events in the last 500 million years. The eruptions continued for roughly two million years and spanned the Permian–Triassic boundry, or P–T boundary, which occurred around 251.9 million years ago.


c. 248 M

Friedrich August von Alberti (DE) first used the term Triassic (Trias) when he named the three-division sequence of sandstone: 1) variegated (Bunter) sandstone, 2) shell (Muschelkalk) sandstone, and 3) Keuper sandstone (1399). The Triassic Period of the Mesozoic Era was a time of transition following a mass extinction of life, with the survivors of that event spreading and recolonizing.

The organisms of the Triassic can be considered to belong to one of three groups: holdovers from the Permo-Triassic extinction, new groups which flourished briefly, and new groups which went on to dominate the Mesozoic world. The holdovers included the lycophytes, glossopterids, and dicynodonts. While those that went on to dominate the Mesozoic world include modern conifers, cycadeoids, and the dinosaurs.

Rocks rich in Triassic fossils include: the Moenkopi Formation, Arizona; Ischigualasto Badlands, Argentina; Newark Supergroup, Eastern U.S.A.; Djadochta, Mongolia; and the Chinle Formation, Arizona.


Thomas M. Harris (GB) presented excellent evidence of mosses in the Triassic of England (638; 639).


c. 245 M

S. Blair Hedges (US) and Laura L. Polong (US), Ying Cao (JP), Michael D. Sorenson (US), Yoshinori Kumazawa (JP), David P. Mindell (US), and Masami Hasegawa (JP) reported in a study of both nuclear DNA and mitochondrial DNA that the turtle is anapsid and the closest living relative of the crocodile. The results apparently establish a phylogenetic joining of crocodilians with turtles and place squamates at the base of the tree. This work presents molecular time estimates to support a Triassic origin for the major groups of living reptiles and supports the previous findings of James E. Platz (US), J. Michael Colon (US), John A.W. Kirsch (US), Gregory Christian Mayer (US), Rafael Zardoya (ES), and Axel Meyer (DE) (269; 651; 790; 1089; 1496).


c. 223 M

During the Carnian-Norian mass extinction event whole categories of animals abruptly vanished from the fossil record. Dinosaurs flourished, probably filling niches left empty when earlier successful types of animals suddenly were wiped out. Within a few million years, dinosaur remains accounted for 25 to 60 percent of the fossils. By 202 million years before the present, dinosaurs were diverse, sometimes gigantic, and dominant among land animals.

Paul E. Olsen (US), Dennis V. Kent (US), Hans-Dieter Sues (US), Christian Koeberl (AT), Heinz Huber (US), Alessandro Montanari (IT), Emma C. Rainforth (US), Sarah J. Fowell (US), Michael J. Szajna (US), and Brian W. Hartline (US) located a crater of the proper size and age to mark the landfall of an asteroid which could have had a devastating effect on many life forms. Manicouagan in Quebec, Canada is the site of the asteroid crater credited with eliminating competitors of early dinosaurs (1012).


c. 213 M

Alexandre-Theodore Brongniart, Jr. (FR) named the Jurassic Period Jurassique in 1829 for extensive limestone deposits in the Jura Mountains of Switzerland (233). This period was characterized by Great plant-eating dinosaurs roaming the earth, feeding on lush growths of ferns and palm-like cycads and bennettitaleans . . . smaller but vicious carnivores stalking the great herbivores . . . oceans full of fish, squid, and coiled ammonites, plus great ichthyosaurs and long-necked plesiosaurs . . . vertebrates taking to the air, like the pterosaurs and the first birds . . . this was the Jurassic Period, beginning 213 million years ago and lasting for 70 million years of the Mesozoic Era.

Rocks rich in Jurassic fossils include: the Lias Formation, England; Navajo Sandstone, Arizona; Solnhofen Limestone, Germany; and the Morrison Formation, Colorado/Utah/Wyoming.


Edwin H. Colbert (US), curator of the American Museum of Natural History, found a massive quarry of Coelophysis dinosaurs in New Mexico and concluded from their skeletons that these Triassic dinosaurs were swift runners with a bird-like posture (335; 336).


c. 200 M

S. Blair Hedges (US), Patrick H. Parker (US), Charles G. Sibley (US), and Sushi Kumar (US) used a comprehensive set of genes that exhibit a constant rate of substitution to estimate the time at which avian and mammalian orders diverged. Their estimates of divergence times averaged about 50-90% earlier than those predicted by the classical methods and show that the timing of these divergences coincides with the Mesozoic fragmentation of emergent land areas. This suggests that continental breakup may have been an important mechanism in the ordinal diversification of birds and mammals (650).


Albert Charles Seward (GB) and Jane Gowan (GB) found fossil records indicating that the ginkgo or maidenhair tree, Ginkgo biloba, has existed on Earth since the Liassic (early Jurassic) period meaning it has inhabited earth longer than any other tree; 200-176 M (6; 115; 380; 891; 1245)