It absolutely is not ethical. It's basically humanity playing God and probably making a big mistake while at it. I could see an argument for species extinct due to human activity in the recent era; but something like mamooths or dinosaurs should be a big no no.
Since humanity is made in the image of God, humanity "playing God" isn't itself morally disqualifying. Motivations, methods, proportionality, and anticipated effects on the human spirit and the natural world have to be considered. That does rule out
most of what people talk about when they talk about "playing God", but it's not clear to me that it rules out cloning a few mastodons or cave bears here and there.
