I know megafauna is not a very common word, while fauna is more so. Fauna is singular, defined as a group of animals. ex. "The African fauna is diverse".
Megafauna is the word defining all animals with body mass larger than a certain threshold (45kg, 100kg, etc), so in theory is still a group. Following this logic, megafauna should be singular.
However in many prominent scientific publications, for example some articles in Science and Nature, you find megafauna used in the plural form. ex. "Megafauna are a major draw for tourists" or "megafauna are imperiled".
Checking online some dictionaries define it as plural and singular. Are these scientists grammatically "wrong" by using megafauna as a plural noun, or are they simply setting the standard for how a word should be used since language evolves and they are the most expert on the subject?