Nights and Dragons— From the memoir of author Abigail Prynne

As I started my research, I discovered many skeptics. Scientists presented evidence to show why dragons could not—and did not—exist. They explained that it would be impossible for dragons to fly because they would be too big. They laughed at the idea of dragons breathing fire. They pointed out that no other animal has ever done this. They said that if dragons had lived, someone would have found remains somewhere in the world. No bones about it, there were plenty of logical explanations. It would have been easy for me to accept that the only place dragons ever existed was in the imaginations of those who believed.
(Re-posting)
Which line from the text implies that scientists do not believe that dragons exist?
They explained that it would be impossible for dragons to fly because they would be too big.
They laughed at the idea of dragons breathing fire.
They pointed out that no other animal has ever done this.
No bones about it, there were plenty of logical explanations.