TOEFL Integrated Writing Practice Test 042Fossils

Animal fossils typically offer limited chances to study actual tissues, as living tissues are largely replaced by minerals during fossilization. However, scientists were recently thrilled when a 70-million-year-old fossil of a Tyrannosaurus rex (T. rex) appeared to contain remnants of the animal’s original tissues. This discovery occurred when researchers intentionally broke open the T. rex’s leg bone, exposing what seemed to be blood vessels, red blood cells, and collagen matrix.

First, when the fossilized leg bone was broken, numerous small branching channels inside the bone were revealed. These channels likely correspond to the spaces where blood vessels once existed. Remarkably, a soft, flexible organic substance was found inside these channels, which may very well represent the remains of T. rex’s actual blood vessels.

Second, a microscopic analysis of the bone’s interior revealed spherical structures that could be remnants of red blood cells. These spheres contained iron, an essential element in red blood cells responsible for transporting oxygen. Additionally, the spheres had dark red centers—consistent with iron’s tendency to be reddish—and were the approximate size of red blood cells.

Finally, scientists conducted a test on the dinosaur leg bone, which confirmed the presence of collagen, a fibrous protein essential to living bone tissue. Collagen forms a structural matrix in bone tissue, and its presence in the fossil is precisely the type of biochemical material expected in association with bone tissue.