There were so many problems with the Voth and that entire episode.
One little example is that hadrosaurs ate plants, but we see the Voth chowing down on insects chameleon style. I grant though that a lot can happen in 65 million years.
Much, much worse however, was the holodeck scene. The doctor says the last common ancestor that the Voth had with the humans was Eryops, from the Devonian - 400 million years ago. This is all wrong. Eryops was from the early Permian, about 295 million years ago. Secondly, Eryops was not the last common ancestor of "warm blooded and cold blooded organisms." Eryops was a Temnospondyl, a group which is generally considered to be related to modern day amphibians (and certainly lived like an amphibian). The common ancestor of reptiles and mammals was an amniote - probably something very small and lizard-like. Warm-blooded and cold-blooded organisms did not split apart at one time, given birds are dinosaurs and evolved endothermy separately (though I grant perhaps hadrosaurs perhaps could have been cold blooded - we don't know when warm blood evolved. Finally, the actual model shown doesn't look anything like Eyrops, but more like a primitive Synapsid ("mammal-like reptile).
The other big problem with that scene was that it repeated Threshold's misconception that evolution was predictable and goal-oriented. Janeway gives this command to the computer:
This request is utterly absurd and should be impossible to meaningfully answer, but in a heartbeat the holodeck generates something reminiscent of a Pertwee-era Silurian* to stand before them. Remember that this is before the Voyager crew know anything about the Voth's home environment or the events that the species have experienced in all those millennia, without which there is no way to predict their evolutionary path."If the Hadrosaur had continued to evolve over the last sixty-five million years, extrapolate the most probable appearance."
*Yes, I am aware that the name of the Silurians is itself an example of bad science.