In the passage, the author states that there is remarkable evidence to consider that dinosaurs were endotherm animals (that is, animals which can keep their body temperature constant). Nevertheless, in the lecture, the teacher disagrees, pointing out different facts which discredit that evidence.
In the first place, the author explains that, since many dinosaur fossils have been found in polar regions, the only way they could have survived there was by controlling their body temperature. Secondly, he suggests that the position and movement of the legs are another factor to be taken into account, since "the legs of all modern endotherms are underneath the body"; and that was the case of the dinosaurs. Finally, the author mentions that the presence of Harvesian canals (canals which allow the rapidly growth of living animals and their bones) is another indicator which supports that idea.
In contrast, the teacher claims that the discovery of dinosaur fossils in polar regions does not mean that they were endothermic. In fact, in the past those places were much warmer than today and, in colder seasons, many of them migrated to warmer areas. Moreover, she indicates that they had that particular position and movement of the legs to support more weight. What is more, the professor notes that dinosaurs presented a rapidly or slowly growth of certain bone rings, which indicated periods of time, depending on the season. However, endotherm animals show rapid growth even when the environment becomes cool.