Complex sentence: According to Heptner and Sludskii (1972), Chernyshev (1953) said that they were formerly recovered from the African lion, and they remarked that the lion's range often overlapped with that of the tiger.
Split into simpler sentences: According to Heptner and Sludskii (1972), Chernyshev (1953) said that they were formerly recovered from the African lion. Thus Heptner and Sludskii remarked that the lion's range often overlapped with that of the tiger.