Simplify the following text for a Grade 11 native English-speaking person.
Original: Lactation and fur , along with other characteristically mammalian features , are also thought to characterize the Mammaliaformes , but these traits are difficult to study in the fossil record .
Simplified: Lactation ( milk ) and fur , along with other features , also characterize the Mammaliaformes , though these traits are difficult to study in the fossil record .