The Paleozoic Era

The author and his colleagues specifically chose to focus on 375 million year old rocks in their search for fossils because this was the time frame that provided fish that would be useful to study from. The 385 million year old rocks provided fish that look too similar to the ones we have now and the 365 million year old rocks have fossils that don’t resemble fish. The 375 million year old rocks, however, provide fossils that show the transition between fish and land living animals.

The Tritheledont, found in rocks that, according to the law of superposition were 190 million years old, had teeth and other skin features such as scales like mammals and reptiles, respectively.

The Cambrian Period marks the beginning of the Paleozoic Era. This period gets its name from a place in Wales where the first examples of this type of ancient life was found. The period lasted for nearly 53 million years, from about 543 million years ago until 490 million years ago. The Cambrian Period marks an important point in the history of life on earth; it is the time when most of the major groups of animals first appear in the fossil record. This event is sometimes called the "Cambrian Explosion", because of the relatively short time over which this diversity of forms appears. It was once thought that the Cambrian rocks contained the

The argument the author puts forth is that horseshoe crabs have evolved over the eras. That they’re not “living fossils”. Horseshoe crabs have “rounded cephalic shields, that were like the extinct trilobites, and an arrangement of legs and gills”, no wonder people think they are living fossils. This is the beginning to how these historic animals have evolved.

Just last year, some researchers stated that the extinct aquatic animal, the ‘Tully Monster’ was a vertebrate, possibly a relative of today’s lampreys. Like a mismatched puzzle, the Tully monster lacks some vertebrate pieces and has others that are the wrong shape, researchers and colleagues report in the March issue of Palaeontology. (Palaeontology includes the study of fossils to determine organisms' evolution and interactions with each other and their environment, their paleoecology).

Most Cambrian rocks contain fossils of trilobite shells, cap-shaped or flattened shells, and brachiopods (Whittington, 1985). When Walcott went looking for North American Cambrian fossils in August of 1909, he ended up in the Canadian Rocky Mountains. He and his wife found a loose block in the ridge they were searching near, split it open, and found what they later classified the “lace crab” (Briggs, 1994). Walcott knew right away what they had discovered was something different – the soft parts of the crab, such as the limbs, were preserved. During the next season, Walcott and his sons came back to the Shale, searching the slopes along the trail where they had discovered the loose block to find fossil layers. Luckily for them, the Shale rock layers were almost horizontal, and for thirty days a team quarried the ridge. The next year, they spent even longer quarrying. The last year spent quarrying the rocks was in 1917, when Walcott was 67 (Briggs, 1994). The rocks were removed from the ridge using picks, chisels, long iron bars, and small explosives. All the quarrying done by Walcott and his crew resulted in over sixty five thousand fossils, now stored in the

The author and his colleagues chose to focus on 375 million year old rocks in their search for fossils because amphibians that look dissimilar to fish were discovered in 365 million year old rocks, while fish without amphibian characteristics were discovered in 385 million year old rocks. Thus, it is possible that the evolutionary intermediary, or the “missing link” between fish and amphibians, would be discovered in 375 million year old rocks, between the two time periods. The rocks examined were sedimentary in composition, as the gradual and relatively gentle formation of sedimentary rock under conditions of mild pressure and low heat are conducive to the fossilization of animal remains. Sedimentary rock is also often formed in rivers and seas, where animals are likely to live. This site provides a resource that describes means by which fossils are formed and how the fossil record may be interpreted, and shows some examples of fossils demonstrating evolution through geological periods: http://www.fossilmuseum.net/fossilrecord.htm. In 2004, Shubin and his colleagues were looking for fossils on Ellesmere Island, in northern Canada. This location was chosen because of its lack of human development, as well as of obstructing natural formations and life forms such as trees, which

The dinosaurs appeared after the greatest mass extinction event occurred. This is known as the Permian-Triassic extinction. It has been estimated to have occurred around two hundred and fifty million years ago. (6) It is also known as the Great Dying with over ninety percent of species dying off, leaving the Earth essentially a wasteland. It led to the extinction of “57% of all families, 83% of all genera and 90% to 96% of all species. 53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species, including insects.”(7) By the late-Permian, global temperatures were very hot, with them being the highest ever on the planet.

Through the changing of the tides the Semibalanus were settling at the top for some time but by day 28 many have taken over the bottom layer of the rock face. It is almost as the Semibalanus barnacles have conquered the bottom region as there are very few Chthamalus to been seen. Above the 2-meter mark on the rock face the Semibalanus are scattered and few can be seen. The Chthamalus are greatly observed on the higher region of the rock face. When it was day 7 there were many Chthamalus barnacles on the bottom of the rock face and by day 28 few can be observed.

In fact the K-T Mass Extinction Event happened 65 billion years ago. That’s a long time. The K-T Mass Extinction Event is the event that happened when all of the dinosaurs went extinct (when the asteroid came and killed off all of the dinosaurs). Though scientists aren’t sure exactly when, they believe that triceratops’ roamed the earth about 65-70 billion years ago. That was around the same time as the K-T Mass Extinction Event. Which means that triceratops’ were one of the last dinosaurs to live. Though they seem really old to us, they were actually alive towards the end of the dinosaur age, during the Cretaceous Period. So they are considered not so old for dinosaurs. Or compared to the

Isotopic profiles of mollusks provide insight to the biology of fossil and living specimen and the conditions under which they live in. Isotopic profiles record seasonal variance in temperature, salinity, dissolved oxygen concentrations and can provide evidence of changes in bio mineralization in correlation with seasonality and ontology. The shells of Tridacna are beneficial for Pleistocene paleoceanography isotopic studies because of their large size making it easier to gain detailed samples of shell carbonate. The density of the shell better preserves original carbonate of the shell.

The formation of Earth, 4.5 billion years ago till the evolution of hard-shelled animals, about 500 million years ago, is called the Precambrian period. There are many events during this time that are specific and affect the Precambrian life. The earth was formed and the first tectonic plate arose and began to move which caused many variations on the earth conditions during Precambrian that affected atmospheric composition and oceans. The level of oxygen arose in the atmosphere which enabled the enrichment of atmosphere with oxygen reaching its peak about 600 million years ago which enabled the first appearance of animal life that required oxygen for the production of collagen and the formation of skeleton. Also, during this period the ozone

     The early tetrapods were the first vertebrates to actually walk the solid earth. They began their conquest of land in the Paleozoic era around 360 million years ago. The question many paleontologists have been asking for a long period of time is whether the anatomy for locomotion on land was developed in water for swimming purposes, or if it was adapted after the creatures became terrestrial. Recent findings of fossils indicate that the transformations of the aquatic creatures happened underwater in order to help them survive in the changing world. When looking for answers, they had to examine forearm, hip, wrist, finger, and other bones, as well as the lungs or gills of the early tetrapod fossils.

The evolutionary history of arthropods date back to the Cambrian period about 540 million years ago. Through trace fossils, scientist have been able to identify and distinguish the first arthropod to be an Euthycarcinoids. Scientist believe that Euthycarcinoids could have been the first animal to colonize in a terrestrial environment. Euthycarcinoids eventually became extinct over the next years. Arthropods started evolving through tagmosis and the specialization of appendages. Tagmosis occurs in the body when different body regions were fused together. Scientist believe that arthropods have evolved up to four times over the millions of years. There are three evolutionary lineages within the phylum arthropoda which include trilobita,

My outside source for questions 3 and 4 is a journal by Pat Shipman titled Fossils. This journal was published in The New Scientist Vol. 215, Issue 2876, p. 8-16.