Complex sentence: The lion's skull has broader nasal openings than the tiger, however, due to the amount of skull variation in the two species, usually, only the structure of the lower jaw can be used as a reliable indicator of species.
Split into simpler sentences: The lion's skull has broader nasal openings than the tiger. However, due to the amount of skull variation in the two species, usually, only the structure of the lower jaw can be used as a reliable indicator of species.