47. It was once thought that there were only two species of squirrel monkeys. how to write again with ONCE
-> there was

In early times, there were two species but with more study we know that there were five species of squirrel monkey.

Explanation:

From the old times until now, people thought that there were only two species of squirrel monkeys i.e. a South American species named Saimiri sciureus and a Central American one, also called Saimiri oerstedti, but with the help of genetic tools, the genus has been reclassified into five species on the basis of genetic, physical, and behavioral characteristics.