Finding Your Inner Fish: Discussion Questions

During the embryonic period, the rate of cell differentiation intensifies, support system for the cells form, and organ appear. In week 3, an embryo, the person-to-be is just 1/10 of an inch (2mm) long. It has become elongated, and three layers emerge – the ectoderm, mesoderm, and endoderm. In week 4, the embryo is so curved that the two ends almost touch. The outer layer (ectoderm) folds into the neural tube. From the mesoderm, a tiny heart forms and begins to beat. The endoderm differentiates into a gastrointestinal tract and lungs. Between days 21 and 28, eyes develop. In the following week, ears, mouth, and throat take shape. Arm and leg buds appear. The handplate from which fingers will emerge appears. The heart divides into two regions, and the brain differentiates into forebrain, midbrain, and hindbrain. In week 6 and 7, the embryo is almost 1 inch long. The heart divides into four chambers. Fingers emerge from the handplate, and primitive facial features are evident. The important process of sexual differentiation begins. During the final week of embryonic period, most structures and organs are present. Ovaries and testes are evident. The embryo begins to straighten and assumes a more human appearance. Clearly, the embryonic period is dramatic and highly important because it is when the structures that make us human evolve. Yet most pregnant women, either because they do not yet know they are pregnant of do not appreciate

Germ cells: the sexual reproductive cell at any stage from the primordial cell to the mature gamete

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

As the rock was rising, it eventually expanded above the water level. The later erption were therefore subaerial. There is some evidence found that the rock was later inhabited by plants and even trees. Figure (....) presents fossilised plants as found in the area.

[1] "Development of the embryo begins at Stage 1 when a sperm fertilizes an oocyte and together they form a zygote."

Have you ever wondered how fossils form in the environment? Will, if you didn’t this is for you. The first stage of the “Fossilization” is when a type of animal dies in a watery environment and is then covered by mud. Then the soft tissues like muscle decompose leaving behind the hard bones, and maybe shells. Next, over time minerals like rock, soil, and others settle over the bones and hardens them to rock along with the others. Then you have your fossil. One of the most unusual fossils is when

This process is called organogenesis. Many organs contain cells from more than one germ layer, and it is not unusual for the outside of an organ to be derived from one layer and the inside from another. For example, the outer layer of skin comes from the ectoderm, while the inner layer (the dermis) comes from the mesoderm. Also during organogenesis, certain cells undergo long migrations from their place of origin to their final location. These migrating cells include the precursors of blood cells, lymph cells, pigment cells, and gametes. Most of the bones of our face are derived from cells that have migrated ventrally from the dorsal region of the

1988, 1990). The presences of fossils in its formation are nearly not present. However, the presence of large number of sedimentary ooids and oval-shaped crinoids’ fossils implied its age to be Early Carboniferous (Fleming et al. 1975).

The fossil record provides a unique view into the history of life by showing the forms and features of life in the past. Fossils tell us how species have changed across long periods of the Earth’s history. For instance, in 1998, scientists found

Dr. Terry Mortenson in the article The Origin of Old- Earth Geology and its Ramifications on Life in the 21st Century, discusses a well know debate that goes back many years. In this review I will give a brief overview of what the article itself is about. Along with that, I will discuss some of the strengths and weaknesses that I have found and thought about. There are some very great points in this article, as well as weak points. I think it is important to discuss both.

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.

These techniques led to the discovery of the boundary between the two eras. A single thin layer of clay found within predominantly limestone rocks established this. By comparing the marine life found in, above, and below the clay, the marine life, like the dinosaurs, had been terribly affected by the extinction event. The percentage of life in the upper layers was dramatically lower than that in the lower. This was far more compelling than what was suggested by dinosaur’s fossils.

As such, the materials reported in this study will cluster primarily around a time bracket of c. 13,000-9,000 BP, which is an approximate temporal median of the Paleoamerican period [c. 15,000-7,000 BP].

Ostracoderm was regarded as the primitive and oldest chordates according to (Gregory 1995).They possessed small fins i.e. medial fins but they lacked lateral fins. Their mouths were always open. Their body size is small with non beyond 15 cm long.