Reading
Endotherms are animals such as modern birds and mammals that keep their body temperatures constant. For instance, humans are endotherms and maintain an internal temperature of 37°C, no matter whether the environment is warm or cold. Because dinosaurs were reptiles, and modern reptiles are not endotherms, it was long assumed that dinosaurs were not endotherms. However, dinosaurs differ in many ways from modem reptiles, and there is now considerable evidence that dinosaurs were, in fact, endotherms.
Polar dinosaurs
One reason for believing that dinosaurs were endotherms is that dinosaur fossils have been discovered in Polar Regions. Only animals that can maintain a temperature well above that of the surrounding environment could be active in such cold climates.
Leg position and movement
There is a connection between endothermy and the position and movement of the legs. The physiology of endothermy allows sustained physical activity, such as running. But running is efficient only if an animal's legs are positioned underneath its body, not at the body's side, as they are for crocodiles and many lizards. The legs of all modern endotherms are underneath the body, and so were the legs of dinosaurs. This strongly suggests that dinosaurs were endotherms.
Haversian canals
There is also a connection between endothermy and bone structure. The bones of endotherms usually include structures called Haversian canals. These canals house nerves and blood vessels that allow the living animal to grow quickly, and rapid body growth is in fact a characteristic of endothermy. The presence of Haversian canals in bone is a strong indicator that the animal is an endotherm, and fossilized bones of dinosaurs are usually dense with Haversian canals.
范文
The professor actually contradicts the statements made in the passage. She is of the view that dinosaurs are not endotherms i.e. they were not able to keep their body temperature at a constant rate.
The professor contradicts the issue of dinosaurs being endothers based on the availability of fossils being available in thwe polar regions, she say that the polar regions in those days were not as cold as they are today i.e at least warm enough for dinosaurs to live. Durin harsh winters she says that there is a possibility of the dinosaurs actually migrating to warmer regions.
The issue of leg position and movement being used as a reason to clasify the dinosaurs as endotherms does not please the professor either. She says that dinosaurs had legs under their bodies to support their huge bodies i.e the legs under the body of the dinosaur were actually to support the huge weight of the dinosaur and not to provide it with a body structure like endotherms(which is actually suited for running).
The professor acknowledges the presence of haversian canals but also points out that that the fossils show the presence of growth rings. These rings occur due to the thickening of the bone. The thickening indicates that the dinosaurs were'nt actually growing continuously but were experiencing periods of rapid growth and periods of no growth in succesion. This pattern she says is characteristic of non endothermic animals.
Thus it can be inferred that the professor challenges the passage by giving reasons as to why she thinks that the dinosaur is not an endotherm.
