I’m writing a research paper about endangered animals. I need help choosing a species!

I’m writing a thesis/research paper on how all animals play an important role on the environment. I’m trying to narrow my paper down on an endangered species but I’m having trouble deciding/thinking of a species that play IMPORTANT roles (ie.- honeybees). Except I cannot choose honeybees as my topic. My intro paragraph is as follows (subject to change):

[Throughout the world, you will find several animal species that are hanging onto the threads of their lives. The extinction of animal species affects us on aspects that we may not consider. There are more to these animals than just their “rarity”. All forms of life are intertwined with each other, playing crucial roles our ecosystems. By allowing animal species to face extinction, you are slowly destroying your own planet. ]

I need help narrowing my paper down to one specific animal/plant species in order to strengthen it.