UALR Paleobiology ERSC 3360

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University of Arkansas at Little Rock Paleobiology ERSC 3360


This is a collaborative effort by the students of Paleobiology 3360. In addition to serving as a communal study aid in the course, the class will build a knowledge base that will be useful to them beyond the class experience, as well as providing a resource for others. By participating in the wiki, the students will not only share their knowledge with each other, they will expand that knowledge beyond what is covered in class and in the book to include resources uncovered by their own quests for knowledge.

Paleobiology 3360 introduces students to the study of paleontology, the study of ancient life. The course covers many aspects of this very broad topic; among them, taphonomy, systematics, evolutionary concepts, paleoecology, paleobiogeography, and others. It will also include a survey of life on Earth, starting from the very beginning to modern times.

Five Major Mass Extinctions

Late Ordovician

Ordovician period was the second most devastating mass extinction in earth's history. The Ordovician period lasted from 510-438 mya and the extinction began in 440 mya and lasted for ten million years. The marine community was the hardest hit; approximately 75% of all marine life was eradicated. The disappearance of 1/3 of all brachiopods and bryozoan was probably due to the extreme cold, lowering sea level and exposed reefs. Numerous groups of conodonts, trilobites, and graptolites were hit hard. Most of all, reef building fauna were decimated. Altogether more than one hundred families or marine invertebrates were wiped out completely. The open niche was filled with species adapted to survive the freezing temperatures, other species that did not die off moved closer to the equatorial region. Most of the major groups that survived were very similar to the extinct faunas, the major carnivores were still nautiloid cephalopods and brachiopods were still the most common organisms.

The Ordovician mass extinction has been theorized by paleontologists to be the result of a single event; the glaciation of the continent Gondwana at the end of the period. Evidence for this glaciation event is provided by glacial deposits discovered by geologists in the Saharan Desert. By integrating rock magnetism evidence and the glacial deposit data, paleontologists have proposed a cause for this glaciation. When Gondwana passed over the north pole in the Ordovician, global climatic cooling occured to such a degree that there was global large-scale continental resulting in widespread glaciation. This glaciation event also caused a lowering of sea level worldwide as large amounts of water became tied up in ice sheets. A combination of this lowering of sea-level, reducing ecospace on continental shelves, in conjunction with the cooling caused by the glaciation itself are likely driving agents for the Ordovician mass extinction. There is also some speculation that the cause was a brief glacial interval that produced two pulses of extinction. The first pulse was at the beginning of the glaciation, when sea-level decline drained epicontinental seaways, produced a harsh climate in low and mid-latitudes, and initiated active, deep-oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths. Following that initial pulse of extinction, surviving faunas adapted to the new ecologic setting. The glaciation ended suddenly, and as sea level rose, the climate moderated, and oceanic circulation stagnated, another pulse of extinction occurred. The second extinction marked the end of a long interval of ecologic stasis. Earth and Planetary Sciences; Volume 29, 2001 / Sheehan, pp. 331-364

Article contributed by Tim Dreher, 7 March 2011

Our best understanding of ice ages is that they are cyclical events based upon the earth’s slightly elliptical orbit around the sun. However, there are some that suggest that the Ice age that occurred around the time of the Ordovician Extinction may have been caused by a Gamma-ray burst. Gamma-ray bursts (GRB) are focused bands of X-ray and Gamma radiation emanating from extraterrestrial sources. They are likely the result of gravitational collapse during a supernova. Although the effects will be confined to one side of the earth, prevailing winds would spread its effects globally. There are several effects that can result from a GRB striking the earth. The greatest effect will be from ozone depletion causing an increase in UV radiation. An increase of UV would have been fatal to a variety of organisms. Particularly affected would have been the phytoplankton, the base of the marine food chain and primary oxygen producer. GRB would also have an devastating effect in the upper atmosphere. It is estimated that a large GRB could penetrate in to the stratosphere where most of the earth’s ozone is located. Here, the intense levels of radiation react with the Nitrogen and Oxygen forming NO2 (nitrous oxide). The brown NO2 would filter out large amounts of the sun initiating an ice age. Ice trapped in glaciers would lower sea levels causing additional damage to life on earth. The patterns of extinction during the end of the Ordovician would be consistent with the expected results of a GRB; the initial influx if UV followed by a weakened ozone layer triggering a global cooling followed by global warming from a weakened ozone layer.

3 A.L. Melott, B.S. Lieberman, C.M. Laird, L.D. Martin, M.V. Medvedev, B.C. Thomas, J.K. Cannizzo, N. Gehrels and C.H. Jackman (2004). Did a gamma-ray burst initiate the late Ordovician mass extinction?. International Journal of Astrobiology, 3, pp 55-61 doi:10.1017/S1473550404001910

Late Devonian

What caused the late Devonian mass extinction?

Scientists have long theorized that the mass extinction in the late Devonian was caused by two possible events. The first of these two events was changes in sea levels and anoxia, possibly caused by widespread global cooling/glaciation of Gondwana or oceanic volcanism. The widespread anoxia,or lack of oxygen, helped to slow or prevent decay in many cases. This would cause a great accumulation of organic matter. This organic matter would one day become oil and would seep into the porous coral reefs of the Devonian seas. This is one reason why Devonian rocks are a valuable source of oil. The second of the events scientist theorized might have caused the late Devonian mass extinction was a meteor impact at the Frasnian-Famennian boundary. This has been proposed by some scientist even though there is not enough evidence to make a conclusive argument.

The late Devonian extinction primarily affected those organisms in the marine environments. One of the most important groups to have been affected was the Cnidaria, and more specifically the warm-water Anthozoa. Many other marine groups were affected as well such as the trilobites, brachiopods, and many jawless fish. This was ,however, more of a marine extinction in that most of the newly developing flora and the primitive arthropods were left relatively unaffected.

The late Devonian extinction was particularly known for the loss of pentamerid brachiopods, armored jawless fish, and the placoderms (the first jawed fish). Endemic species were decimated and were replaced by cosmopolitan species, one of the biggest pieces of evidence indicating that the oscillating sea level changes allowed high levels of species invasions. In effect, the extinction event was a biodiversity crisis that wiped out species with small ranges.

Late Permian

Life Struggles In The Late Permian

    In the history of life on planet Earth, no event is more startling or distinctive than the late Permian extinction event. Approximately 251 million years ago, 50-54% of existing families, 68% of genera, and 80-96% of species became extinct. This biological nightmare is well examined in a study of the Meishan section in south China. It was found here, that out of 333 identifiable species, at least 161 of these became extinct before the boundary with the Triassic.
    Some widespread and common groups suffered extinction. Some examples include: The Fusulinid Foraminiferans, The prevalent corals found in the orders Rugosa and Tabulata, Blastoid echinoderms, Inadundate and Camerate crinoids, Trilobites, Eurypterids (sea scorpions), many bryozoans, Orthid and Proctid brachiopods. Advanced lifeforms like fish, such as Acanthodians, most woody plants, and tetrapods such as Pelycosaurus could not adapt. Among the surviving species, all suffered tremendously.
    Thankfully, not all life perished. Some forms survived through the extinction, and even took advantage of it. Some groups of crinoids and echinoderms survived, and subsequently prospered. The brachiopod Lingula and the bivalve Claraia, both became cosmopolitan and spread worldwide. The main surviving tetrapod (and one of very few), Lystrosaurus, an omnivore, did not become widespread. This was the case with tetrapods for millions of years, as they struggled to spread and diversify. This is in contrast to the important ecological roles and common diversity of tetrapods such as amphibians held before the Permian extinction. Fungal organisms also flourished after the Permian event. Most researchers attribute this fungal bloom to an increase in available food resources for the fungi, due to the accumulation of dead organic matter.
    Due to the immense Permian die-off, the fauna that we are now familiar with, and associate with the Mesozoic was allowed to evolve. Without this event, life in the Mesozoic and beyond may have been markedly different.

    1. Benton, Michael J. and R.T. Twitchett. "How to Kill (Almost) All Life: The End Permian Extinction Event". TRENDS in Ecology and Evolution. Vol. 18 No. 7. July 2003.

   2. Knoll, Andrew H. "Paleophysiology and End-Permian Mass Extintion". Earth and Planetary Science Letters. Vol. 256. Issues 3-4. 30 April 2007.

Article contributed by Lowell Sherrod, 6 March 2011.


Late Permian, Prevailing Hypothesis of Causation

It is lead to believe that the Siberian flood volcanism is the event that lead to the mass extinction in the Permian period. In Siberia giant volcanic eruptions occurred, spewing out 2 million km of basalt lava covering most of eastern Russia. The mass eruptions lasted for up to one million years. The eruptions released huge amounts of carbon dioxide and sulfur gas into the earths atmosphere. The sulfur gases created acid rain while the carbon dioxide entered the sea waters making it harder for calcified species to build their shells. The magma rising through coal beds released methane gases, and when released into the atmosphere it becomes a greenhouse gas causing global warming. Carbon dioxide gas and aerosol would enter the lower stratosphere with volcanic eruptions at this magnitude. This would reduce the sunlight from reaching the earth’s surface. As a result, not only would the atmosphere be cooled, but the photosynthesis would be reduced or even stop if the light transmission was sufficiently impaired. This would cause most of the earth’s plants and animals to die off. The evidence from the Siberian flood Traps have scientist thinking that this is the main cause for the mass extinction in the Permian Period.

P.R. Renne, A.R. Basu, Rapid eruption of the Siberian Traps flood basalts at the Permo-Triassic Boundary, Science 253 (1991) 176-179.

Andy Saunders et al. Chinese Science Bulletin, January 2009. Vol. 54. No. 1. 20-37

Article contributed by Jonathan Oxner, 7 March 2011

Late Permian, An Aternative Hypothesis of Causation

     The cause(s) of the end Permian mass extinction (~251 Million years ago) remain contested with the current prevailing research showing that mass volcanism from the Siberian traps perhaps best fits the evidence for a mechanism that could have triggered the chain of events that lead to the degree of global change sufficient enough to cause the mass extinction event.
     Alternatively, with the high degree of certainty that a major meteor impact precipitated the KT mass extinction, a similar impact was hypothesized to have caused the end Permian event, but the evidence has been equivocal. Becker et al (2001) proposed that sediments from the Permian and Triassic boundary were found to contain argon and helium with isotope ratios characteristic of those found in carbonaceous chondrites (a class of chondritic meteorites) which would point to an impact event (akin to the layers enriched in iridium associated with the impact hypothesis for the KT mass extinction). In 2004, Becker et al claimed that a potential crater site had been found, the Bedout High, northwest of Australia. Seismic and gravitational data are consistent with a buried impact crater, and core samples with melt rocks and impact breccias were also identified from the site. As Benton (2003) stated, “The evidence [for impact causation of the PT mass extinction] is far weaker and more limited than for impact at the KT boundary and it would be premature to construct a killing scenario founded on such evidence.”

Becker L., Poreda R.J., Hunt, A.G., Bunch, T.E., and Rampino, M., 2001, Impact event at the Permian-Triassic boundary: Evidence from extraterrestrial noble gasses in fullerenes:

     Science, v. 291, p. 1530-1533.

Becker L., Poreda R.J., Basu A.R., Pope K.O., Harrison T.M., Nicholson C. & Iasky R., 2004, Bedout: A possible end-Permian impact crater offshore of northwestern Australia:

     Science, v. 304, p. 1469-1476.

Benton, M.J. and Twitchett, R.J., 2003, How to kill (almost) all life: the end-Permian extinction event: TRENDS in Ecology and Evolution, Vol.18 No.7, p. 358-365.

Article contributed by John Hutchison, 6 March 2011.

Late Triassic

The late Triassic mass extinction occurred approximately 200 million years ago. It is one of the lesser understood ME events. Different studies estimate between 35 to 50% of the species on Earth dissappeared from existence. It also marked the beginning of period when the diapsid dinosaur the dominant group.

As for marine life, there is clear evidence that the ammonids, bivalves, and brachiopoda were nearly decimated and that the conodonts were finally pushed to extinction. There was a sharp decline in radiolaria, a major source of food for many filter-feeding marine species. Fifty-eight cephalopod families disappeared, as well as six ammonite families. Palaeocopida, Cytheracea, and Bairdacea populations were markedly decreased. Gastropods lost 13 families. Four marine tetrapod families were lost, leaving only 2 families. Thirteen marine reptile families disappeared, such as the Nothosauras and the Placodont.

As for terrestrial life, pollen and spore counts suggest evidence that the amount of plants declined. Ferns such as the Glossopteridaceae, Peltaspermaceae and Corystospermaceea became extinct. Eight freshwater bony fish families and 35 insect families became extinct. Because of inaccuracies in the fossil record, there is great debate as to what vertebrates went extinct and when. About 20 diverse tetrapod families became extinct, such as the Rhynchosaurs and Thecodonts. Many Archosaur groups did not survive. There is still much dispute upon the exact dating of the Triassic and Jurassic boundary.

University of Bristol,


Article contributed by Mei Travis, 7 March 2011.

Central Atlantic Magmatic Province Theory for Late Triassic Mass Extinction

As the supercontinent Pangaea started to rift apart approximately 200 million years ago, the corresponding volcanic activity that occurred released large flows of basalt. The intensity and brevity of these flows filled the atmosphere with gases that brought about extreme climate change. It is believed that multiple volcanic pulses occurred over a relatively short amount of time, creating enough rapid change in the environment to make it unlikely that most organisms could adapt to the new conditions. The basalt flows are present from South America through North America and over to Western Europe and Africa, speaking to the enormous size of these flows. Dating of outcrops in Morrocco and Eastern North America put the volcanic events near the end of the Triassic, corroborating the idea that these events could have caused the following mass extinction event.

Article contributed by Corbin Cannon, 8 March 2011.

Alternatives to the Central Atlantic Magmatic Province theory: After the acceptance of a bolide impact as the cause for the K-T mass extinction, scientists began to wonder if other asteroid collisions could be responsible for other extinctions. One popular candidate was the Manicouagan impact crater, located in Quebec, Canada. Its crater forms the fifth largest reservoir in the world and the impact was extremely significant. The initial radiometric date for the crater (acquired in 1978) was conducted using Rubidium - Strontium, and produced an age of between 209 and 219 million years before present. Accepting the 200 - 216 Ma date for the extinction event established by Harland in 1990, the Manicouagan impact could have coincided with the end-Triassic extinction event. However, in 1992 Hodych and Dunning acquired another radiometric age date using the Uranium/Lead technique which resulted in the Manicouagan impact predating the Tr-J extinction by 12 Ma.

J. P. Hodych and G. R. Dunning Did the Manicouagan impact trigger end-of-Triassic mass extinction? Geology (Boulder) (January 1992), 20(1):51-54

Article contributed by Nathan Scarborough, 8 March 2011.

Late Cretaceous

With the meteorite impact and volcanic eruptions, came the extinction of dinosaurs, many other small species, land flaura, and most of the land flora, as well. Most of the life on the earth was killed off. It is said that about half of all the genera had disappeared completely, never to be seen again. The dinosaurs were land reptiles, and the biggest animals that ever walked this earth. Including large reptiles of the sea, plesiosaurs, and large flying reptiles. For the sea animals, their food supply died, phytoplankton, because of the lack of sun for photosynthesis. For land animals, the plants died, leading to a snowball effect. Herbivores starved to death, causing carnivores to eventually starve to death, as well. For the animals that were able to hibernate, they somehow survived, and for those that didn't, couldn't survive. This is because the temperature dropped to about -18 degree C. So the smaller more able species survived, along with some avian forms, leaving the dinosaurs and other larger such species to go extinct. Apparently, no terrestrial forms larger than about 25 kg survived the extinction event.

Luis W. Alvarez Experimental evidence that an asteroid impact led to the extinction of many species 65 million years ago Proc. Natl. Acad. Sci. USA Vol. 80, pp. 627-642, January 1983 Geology Article contributed by Carolyn Gipson

The alternate hypothesis to the Asteroid Impact hypothesis that some scientists believe to be the cause of the Cretaceous Extinction is the volcanic theory; a theory that many paleontologists still believe to be the main cause of the dinosaur's demise and thus creating a rift between paleontologists. However, a paper by J.G Negi suggests that a meteroid impact off the coast of Bombay triggered the cataclismic erruption of the Deccan Bassalts that killed the dinosaurs. He states that the conduit structure (the chamber outside a volcano; that "holds" the magma) , with a maximum diameter of about 35 km at its base, may originate from cracking of a weak pre-Deccan trap with shallow upwarped mantle. The structure may have been caused by a bolide impact which triggered the eruption of massive flood basalts (Deccan traps) on the western margin of the fast-moving Indian plate. An impact in this locality can explain the sudden detachment of the arcuate Seychelles block from India as well as the large-scale reorganisation of plate boundaries in the Indian Ocean. Our hypothesis of impact-triggered volcanism at 65 Ma advocates a bimodal cause for the mass extinction at the K-T boundary (189).

J.G. Negi, P.K. Agrawala, O.P. Pandeya and A.P. Singha A possible K-T boundary impact site offshore near Bombay and trigerring of rapid Deccan volcanism. Physics of the Earth and Planetary Interiors Volume 76, Issues 3-4, March 1993, Pages 189-197

Article Contributed by Melissa Rogalla, 8 March 2011.

Placental Mammal Diversification and the Cretaceous-Tertiary Boundary

There are three basic theories for the survival and diversification of the placental mammals crossing the Cretaceous-Tertiary (KT) Boundary (about 65 million years ago [mya]): The Explosive Theory, the Long Fuse Theory, and the Short Fuse Theory. All three of these theories were suggested Archibald and Deutschman, two great scientists of their time. The first theory suggests that both “interordinal and intraordinal diversification” (interordinal meaning diversity happening between the orders and intraordinal meaning diversity happening within the orders) happened after the KT boundary. The second theory agrees with the Explosive theory in that it suggests intraordinal diversification happened after the boundary, but it differs in that it suggests interordinal happened before the boundary. The last theory suggests that there were “interordinal and...intraordinal divergences in excess of 100 mya “ before or shortly after the appearance of eutherians [placental mammals] in the fossil record”” (Springer et al. 1056).

Placental mammal sizes increased after the KT boundary due to the lack of competition being shown by the larger reptiles and birds (Dinosaurs, etc). It allowed the mammals to diversify and spread out, moving from a mainly fossorial lifestyle to life above the ground. The rodent-like animals (mainly Rodentia) still stayed one of the most diverse groups (as the paper goes on to say in the conclusion) and they were also some of the earliest divergences to be found. The study overall favored the Long Fuse theory.

All of the placental mammals that diversified and survived throughout the KT boundary (and also those whose DNA were tested in this study) are listed in this table below, the lineages in which they diverge earliest are written below for easier reading.

Afrosoricida, Carnivora, Cetartiodactyla, Chiroptera, Eulipotyphla, Lagomorpha, Perissodactyla, Primata, Rodentia, Xenartha

Work Cited

Springer, Mark, William Murphy, Eduardo Eizirik, and Stephen O'Brien. "Placental Mammal Diversification and the Cretaceous-Tertiary Boundary." Wayne State University, School of Medicine. 100.3 (2002): 1056-1061. Print.

Article Contributed by Katie Simmons, 8 March 2011.

At the end of the Cretaceous, about 65 million years ago, a great extinction event knocked out nearly half of the living genera. The main hypothesis being considered is that a large asteroid, approximately 10 km across, stuck the earth. This impact created a large dust cloud which rose up to the stratosphere and encircled the earth; blocking out most if not all sunlight for several years. Without sunlight photosynthesis was halted, killing most plants and the animals that fed on those plants, and therefore continuing up the food chain. When the dust finally settled it left a layer of iridium, a rare earth metal commonly found in asteroids, around the globe clearly separating the Cretaceous and Tertiary periods. When plants were able to resume photosynthesis, the ones remaining began to regrow, helping to restart a successful food chain with the animals that survived this great extinction.

Alvarez, Luis W., Walter Alvarez, Frank Asaro, and Helen V. Michel. "Extraterrestrial Cause for the Cretaceous-Tertiary Extinction." Science. 208.4448 (1980): 1095-1108. Print.

Article contributed by Nick Whitten 8 March 2011