As soon as Edward Holmes saw the dark-ringed eyes of the raccoon dogs staring at him through the bars of the iron cage, he knew he had to capture the moment.

It was October 2014. Dr. Holmes, a biologist at the University of Sydney, had come to China to survey hundreds of species of animals, looking for new types of viruses.

On a visit to Wuhan, a commercial center of 11 million people, scientists from the city’s Center for Disease Control and Prevention brought him to Huanan Seafood Wholesale Market. In stall after stall of the poorly ventilated space, he saw live wild animals — snakes, badgers, muskrats, birds — being sold for food. But it was the raccoon dogs that made him pull out his iPhone.

As one of the world’s experts on virus evolution, Dr. Holmes had an intimate understanding of how viruses can jump from one species to another — sometimes with deadly consequences. The SARS outbreak of 2002 was caused by a bat coronavirus in China that infected some kind of wild mammal before infecting humans. Among the top suspects for that intermediate animal: the fluffy raccoon dog.

“You could not get a better textbook example of disease emergence waiting to happen,” Dr. Holmes, 57, said in an interview.

The photos faded from his mind until the last day of 2019. As Dr. Holmes was browsing Twitter from his Sydney home, he learned of an alarming outbreak in Wuhan — a SARS-like pneumonia with early cases linked to the Huanan market. The raccoon dogs, he thought.

“It was a pandemic waiting to happen, and then it bloody well happened,” he said.