The right answer is Mammalia is more specific than Animalia.
Mammals (Mammalia) are a taxon and a clade of vertebrate animals, which are themselves an Animalia taxon.
There are major general characteristics that make it possible to classify Animalia in branch lines.
* Arthropoda
* Mollusca
* Nematoda
* Chordata (Mammalia among others)
* Platyhelminthes
* Annelida
* Cnidaria
* Echinodermata
* Porifera ...