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.
As much as we would like to have the remains of actual dinosaur tissue, there are sound reasons for being skeptical of the identifications made in the reading.
First, the soft, flexible substance inside the bone channels isn’t necessarily the remains of blood vessels. It is much more likely to be something else. Like what? You might say. Well, long after an organism is died, bacteria sometimes colonize hollows, empty areas in bones, like the channels that once held blood vessels. When bacteria lived inside bones, they often leave behind traces of organic material. What the researchers in the reading are identifying as blood vessels might just be traces of soft and moist residue left by bacteria colonies.
All right. What about the iron-filled spheres? Well, the problem is that scientists found identical reddish spheres in fossils of other animals found in the same place. That includes fossils of primitive animals that did not have any red blood cells when they were alive. Clearly, if these spheres appear in organisms that did not have any red blood cells, then the spheres cannot be the remains of red blood cells. The spheres probably have a very different origin. They are probably just pieces of reddish mineral.
Third, the collagen. The problem is that we have never found collagen in animal remains that are older than one hundred thousand years. Collagen probably cannot last longer than that. Finding collagen from an animal that lived seventy million years ago would really contradict our ideas about how long collagen can last. It is just too improbable. The most likely explanation for the presence of collagen is that it doesn’t come from the T.rex, but from another much more recent source. For example, human skin contains collagen, so the collagen may have come from the skin of the researchers who are handling the bone.
Main points: A recently found T.rex fossil might contain actual tissues of the dinosaur.
Sub point 1: Small channels with organic substance inside leg bone could be blood vessels.
Sub point 2: Presence of iron spheres could indicate red blood cells.
Sub point 3: Collagen matrix being showed after a test.
Sub Point 1: Bone channels could be caused by something else like bacteria. (Bacteria leave remains)
Sub Point 2: Iron filled spheres may not indicate any red blood cells. (On no blood cell animal, could be mineral.)
Sub Point 3: Collagen cannot last longer than 100,000 years. (Could be skin)
The lecturer extends possible explanations beyond the conclusions made on the newly discovered T. Rex fossil and suggests that the existing evidence can point to something other than just the remaining animal tissues, as suggested in the reading passage.
First, the branching channels in that leg bone may be traces of colonies of bacteria, since bacteria always take the hollows in a bone structure and grow themselves following the existing contours of organic material. And the soft substance inside the channels could be the residues of these bacteria colonies, rather than desiccated blood vessels, as suggested by the reading material.
Second, the reading assumes the reddish spheres found in the bone are red blood cells, citing their color and size. But other fossils of primitive organisms in the same general area also contain similar reddish spheres. With the knowledge that such primitive organisms could not yet have evolved red blood cells, there is good reason to believe that these spots are only reddish mineral deposits, and not blood cells. The reading again makes an imprudent conclusion here.
Third, not a single sample of collagen found to this date is older than 100 thousand years in age. The collagen found at the site spoken of in the passage, however, is located in a seventy million year-old dinosaur fossil. Since this tissue can hardly sustain such a long history, its source may not be a prehistoric animal, but rather the skin of researchers. Hence, the final conclusion of the reading is cast in doubt.
1. The lecturer extends possible explanations beyond the conclusions(旧的结论) made on the newly discovered (新的现象和证据)and suggests that the (新的结论)
2. Imprudent： 不谨慎的，不明智的
3. It is imprudent of you to lend money to a stranger.
4. Cast in doubt: 有疑问的
/Suspectful / Undetermined/
The old theory has cast in doubt by some newly found evidence.