It is very possible for Emet-Selch to find constellations, but the exact ones will be more of a trial and error. There are many constellations of animals and mythical beasts that could fit. As a hint, he should try to constellations that may match those squiggly lines from the other mural...

While it's preferred that Emet-Selch doesn't figure out all of them by himself (or involved with all of them), he's definitely allowed to have one or two guaranteed! And you are free to create the actual constellation so long as it fits the theme of the leviathan(s) you choose, otherwise just handwaving the details and just saying, "A constellation matching X leviathan" is fine. Let us know which ones you think he'd be able to figure out (or luck into) and if there are others he may be able to help narrow down for others to take credit for. Which ones he figures will determine what will happen next...