The lecturer casts doubt on the view that dinosaurs are endotherms which is held by the reading passage.
First, according to the lecturer the climate of polar regions were warmer in the period when dinosaurs were living so dinosaurs could survive even they are not endotherms. And in the cooler part of a year dinosaurs could emigrate to some warmer place or just hibernate like today's polar region animals. This argument opposes to the assertion of the reading passage which is demonstrated that only endotherms can survive in polar regions in dinosaurs' time.
Second, the lecturer shows that animals legs are positioned underneath their bodies maybe does not mean they can move quickly,like running, and that contrasts to the reading passage's hypothesis. As the lecturer says, there is another explanation, legs that are positioned underneath body can burden more weight so that dinosaur can grow to a large size.
Finally, the reading passage confirms that Haversian canals in dinosaur's body indicates that dinosaur can have a rapid body growth. But according to the lecturer there is evidence that in cooler climate dinosaurs will cease to grow or grow slower and then in the following warmer climate they will grow faster again, but endotherms can have a rapid growth even in cold environment.
In conclusion, the lecturer argues that the reading passage's evidences to prove dinosaurs are endotherms are not convincing. There are a lot of explanations can demonstrate that dinosaurs are not endotherms.