This paper will look at species delimitation. For the longest time, it was uncontroversial where the boundaries of a species were. That is mostly due to the fact that traditionally, species delimitation was based on morphology. Additionally, behavioural, geographical etc. information is used. But more and more you get articles like "one giraffe species is actually 7" and "two tiger species are actually just one species".
With availability of molecular analysis more and more species were flagged as "possibly cryptic". following up on that, experts for that species took a closer look and confirmed the hypothesis.