Factual error: The frequency which is used to attract the dragon fly is said to be "sub-sonic" and therefore can't be heard by humans, but the exact frequency is stated to be 38.2 Hz. This is well above 20 Hz, the lowest frequency an average human can hear.
Revealing mistake: Dr. Shannon identifies the skeleton as being a middle-aged male, but the skull is female. A male skull has a more pronounced ridge over the eye orbits, a sloping forehead, a longer mastoid process, and the skull widens at the back, unlike a female's that is more parallel.
Chosen answer: Because that's where the rift led. They don't have a time-travel machine, capable of taking them wherever they please - all they have is a hole in time leading to one single time period.
Tailkinker ★