Animal fossils usually provide very littleopportunity to study the actual animal tissues because in fossils the animals'living tissues have been largely replaced by minerals. Thus, scientists were veryexcited recently when it appeared that a 70-million-year-old fossil ofTyrannosaurus rex (T. rex), a dinosaur, might still contain remains of theactual tissues of the animal. The discovery was made when researchersdeliberately broke open the T. rex’s leg bone, thereby exposing its insides toreveal materials that seem to be remains of blood vessels, red blood cells, andcollagen matrix.
First, the breaking of the fossilized legbone revealed many small branching channels inside, which probably correspondto hollows in the bones where blood vessels were once located. The excitingfinding was the presence of a soft, flexible organic substance inside thechannels. This soft substance may very well represent the remains of the actualblood vessels of T. rex.
Second, microscopic examination of thevarious parts of the inner bone revealed the presence of spheres that could bethe remains of red blood cells. Tests showed that the spheres contained iron – a materialvital to the role of red blood cells in transporting oxygen to tissues.Moreover, the spheres had dark red centers (substances with iron tend to bereddish in color) and were also about the size of red blood cells.
Third, scientists performed a test on thedinosaur leg bone that showed that it contained collagen. Collagen is a fibrousprotein that is a main component of living bone tissue, in which it forms a so-calledcollagen matrix. Collagen (or its chemical derivatives) is exactly the kind ofbiochemical material that one would expect to find in association with bonetissue.
- Main point: 科学家在研究霸王龙腿骨化石的时候，发现里面存在着可能为血管、血红细胞和胶原蛋白基质的物质。
- Sub point 1: 化石中有血管
- Sub point 2: 化石中有血红细胞
- Sub point 3: 化石中有胶原蛋白
As much as we would like to have theremains of actual dinosaur tissue, there are sound reasons for being skepticalof the identifications made in the reading.
First, the soft, flexible substance insidethe bone channels isn’t necessarily the remains of blood vessels. It is muchmore likely to be something else. Like what? You might say. Well, long after anorganism is died, bacteria sometimes colonize hollows, empty areas in bones,like the channels that once held blood vessels. When bacteria lived insidebones, they often leave behind traces of organic material. What the researchersin the reading are identifying as blood vessels might just be traces of softand moist residue left by bacteria colonies.
All right. What about the iron-filledspheres? Well, the problem is that scientists found identical reddish spheresin fossils of other animals found in the same place. That includes fossils of primitiveanimals that did not have any red blood cells when they were alive. Clearly, ifthese spheres appear in organisms that did not have any red blood cells, thenthe spheres cannot be the remains of red blood cells. The spheres probably havea very different origin. They are probably just pieces of reddish mineral.
Third, the collagen. The problem is that wehave never found collagen in animal remains that are older than one hundredthousand years. Collagen probably cannot last longer than that. Finding collagenfrom an animal that lived seventy million years ago would really contradict ourideas about how long collagen can last. It is just too improbable. The mostlikely explanation for the presence of collagen is that it doesn’t come fromthe T.rex, but from another much more recent source. For example, human skincontains collagen, so the collagen may have come from the skin of theresearchers who are handling the bone.
- Main point: 阅读部分的发现是值得怀疑的
- Sub point 1: 细菌会侵袭死亡有机体，研究人员鉴定为血管的部分可能是细菌的遗迹
- Sub point 2: 含铁红色球状物在其他没有血红细胞的动物化石中也有发现，可能是矿物颗粒
- Sub point 3: 胶原蛋白不可能存在那么长时间，很可能来自于研究人员
The reading passage points out threeevidences that indicate the existence of actually tissue in dinosaur fossil.However, the professor doubts the accuracy of these evidences. In fact, heoffers some alternative explanations for the substances found in the fossil.
First and foremost, he challenges theexistence of blood vessels. Instead, he points out that bacteria may occupy thehollows inside the bones. Therefore, it is highly possible that the soft substancein the branching channels of the bone is the moist residue of bacteria, ratherthan blood vessels of the dinosaur.
Moreover, the professor casts doubt aboutthe red substance in sphere, which according to the reading passage is theremain of red blood cells. In fact, the professor claims that this red substancewas also found in some other animals, which lived in the same place but had nored blood vessels at all. The professor argues that the sphere can be pieces ofred minerals.
Additionally, the professor doubts theexistence of collagen in the fossil. On the contrary to the reading passage, hepoints out that the earliest collagen that has ever found is in fossils 100000 ago.It is unlikely for collagen to last for more than 70 million years. As aresult, the professor suggests that the collagen may come from recent sources,such as the skin of researchers who handed the fossil.