The main idea of the reading and lecture is both about the migrations of dinosaurs. The author of the reading feels that dinosaurs migrated from north to south and gives three reason for support that. The lecturer, on the other hand, utterly challenges the claims made by the author. He is of opinion that the hypothesis in not convincing and present reason to that claims.
To begin with, the author argues that we can conclude from their diet that dinosaurs migrated to south from North Slope. Because they eat some special kind of plant that grow only in temperate zones. This specific argument is challenged by the lecture. He claims that they didn't have to migrate for finding food. Because the North Slope climate was warmer than today. Even there was sun in the sly for 24 hour in peak of summer, so condition for growing plants was suitable. Also in winter, in harsh cold climate, they could eat dead plant due to they were full of nutrients.
Secondly, the writer suggest that dinosaurs were living in herd and alongside herd, they also were migrating. The lecturer, however, rebuts this by mentioning that living in herd, didn't mean they were migrating. Also he mention that, some animals live in herds for being safe from predators. For example, elk live in among herds and don’t migrate with the herd, He is here just for surviving from predators.
Finally, the author states that to make such a journey, dinosaurs had to migrate very long distant. In contrast, the lecturer's position is that dinosaurs can migrate this distant, but the juveniles are not capable to do that. They are so slow, and they reduce the herd's speed, so adult dinosaurs can't live the juveniles behind themselves. as a result, this hypothesis isn't true. 
The main  
idea
 of the reading and lecture is both about the migrations of dinosaurs. The  
author
 of the reading feels that dinosaurs migrated from north to south and gives three reason for support that.  
The
 lecturer,  
on the other hand
,  
utterly
 challenges the claims made by the  
author
. He is of opinion that the hypothesis in not convincing and present reason to that claims.
To  
begin
 with, the  
author
 argues that we can conclude from their diet that dinosaurs migrated to south from North Slope.  
Because
 they eat  
some
 special kind of plant that grow  
only
 in temperate zones. This specific argument  
is challenged
 by the lecture. He claims that they didn't  
have to
  migrate
 for finding food.  
Because
 the North Slope climate was warmer than  
today
. Even there was sun in the sly for 24  
hour
 in peak of summer,  
so
 condition for growing plants was suitable.  
Also
 in winter, in harsh  
cold
 climate, they could eat dead plant due to they were full of nutrients. 
Secondly
, the writer suggest that dinosaurs were living in  
herd
 and alongside  
herd
, they  
also
 were migrating. The lecturer,  
however
, rebuts this by mentioning that living in  
herd
, didn't mean they were migrating.  
Also
 he  
mention
 that,  
some
 animals  
live
 in  
herds
 for being safe from predators.  
For example
, elk  
live
 in among  
herds
 and don’t  
migrate
 with the  
herd
, He is here  
just
 for surviving from predators. 
Finally
, the  
author
 states that to  
make
 such a journey, dinosaurs had to  
migrate
  very
 long distant.  
In contrast
, the lecturer's position is that dinosaurs can  
migrate
 this distant,  
but
 the juveniles are not capable to do that. They are  
so
 slow, and they  
reduce
 the herd's speed,  
so
 adult dinosaurs can't  
live
 the juveniles behind themselves.  
as
 a result, this hypothesis isn't true.