Essay topics: Animal fossils usually provide very little opportunity to study the actual animal tissues, because in fossils the animals' living tissues have been largely replaced by minerals. Thus, scientists were very excited recently when it appeared that a 70-million-year-old fossil of Tyrannosaurus rex (T. rex), a dinosaur, might still contain remains of the actual tissues of the animal. The discovery was made when researchers deliberately broke open the T. rex’s leg bone, thereby exposing its insides to reveal materials that seem to be remains of blood vessels, red blood cells, and collagen matrix.
First, the breaking of the fossilized leg bone revealed many small branching channels inside, which probably correspond to hollows in the bones where blood vessels were once located. The exciting finding was the presence of a soft, flexible organic substance inside the channels. This soft substance may very well represent the remains of the actual blood vessels of T. rex.
Second, microscopic examination of the various parts of the inner bone revealed the presence of spheres that could be the remains of red blood cells. Tests showed that the spheres contained iron-a material vital to the role of red blood cells in transporting oxygen to tissues. Moreover, the spheres had dark red centers (substances with iron tend to be reddish in color) and were also about the size of red blood cells.
Third, scientists performed a test on the dinosaur leg bone that showed that it contained collagen. Collagen is a fibrous protein that is a main component of living bone tissue, in which it forms a so-called collagen matrix. Collagen (or its chemical derivatives) is exactly the kind of biochemical material that one would expect to find in association with bone tissue.
The reading passage argues that the materials found inside a T.rex leg bone are actually remains of blood vessels, red blood cells and collagen from the animal. However, the lecturer, on the other hand, casts doubt on the claims made in the article. He mentions that there are sound reasons to be skeptical about these identifications.
First and foremost, the author contends that the organic substance discovered could be from the blood vessels of T.rex. Nevertheless, the speaker in the lecture challenges this point of view. He holds that bacteria could have colonized the hollow channels and the organic matter is just traces of bacterial colonies.
Secondly, the writer assumes that the spheres unearthed are red blood cells since it contains iron and they are reddish in color. In addition, they are almost the same size of red blood corpuscles. Conversely, the lecturer points out that those objects were also found in primitive animals' fossils at the same site, which are not supposed to have red blood cells when they were alive.
Lastly, the excerpt posits that the confirmation of the presence of collagen proves that the remnants might be of blood vessels. In contrast, the lecturer brings up the fact that the oldest collagen ever detected was from 100,000 year-old fossils. Furthermore, the common belief between scientists is that collagen cannot last longer than that. Hence, the source of this uncovered collagen might be the researchers' skin rather than from the fossil.
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