Dentition describes three separate things about an animal's teeth: how they are fixed into the jaw, whether they are all the same shape, and how many times they are replaced in a lifetime. Mammals need all three terms checked at once.
- Acrodont and homodont: Acrodont means teeth are fused directly onto the top of the jaw bone with no socket, seen in many reptiles and fish, and homodont means all teeth share one shape. Mammals have neither feature.
- Homodont and thecodont: Thecodont (teeth rooted in sockets) is correct for mammals, but homodont is wrong, since mammalian teeth are not all the same shape.
- Acrodont and heterodont: Heterodont (different tooth shapes) is correct for mammals, but acrodont is wrong, mammal teeth sit in sockets, not fused onto the jaw surface.
- Thecodont, heterodont and diphyodont: Thecodont fits, since mammal teeth are anchored in sockets called alveoli. Heterodont fits, since mammals carry incisors, canines, premolars and molars, each shaped for a different job (cutting, tearing, grinding). Diphyodont fits, since mammals grow one set of milk teeth followed by one set of permanent teeth, exactly two generations of teeth across a lifetime.
Only the fourth option gets all three descriptors right at the same time.
Let's summarize:
- Thecodont describes how the tooth is anchored (in a socket), heterodont describes shape variety, and diphyodont describes how many times teeth are replaced.
- Acrodont and homodont belong to other vertebrate groups, not mammals.
So mammalian dentition is thecodont, heterodont and diphyodont.