He's just taking an idea and seeing how it works out.
The next step should be making adjustments for the family cut off, using some metric based on mutation rate or generation length. Using different cutoffs I get the following family numbers in Passeriformes
Applying manageable chunk theory, I'd say a system using 20 mya and 70 families might be able to get some traction. Anything less and the Passeridae becomes too large to be a useful classification. There is also tradition. Halving the the number of families would get enough resistance, anything more and they'd be storming the citadel.
The next step should be making adjustments for the family cut off, using some metric based on mutation rate or generation length. Using different cutoffs I get the following family numbers in Passeriformes
- 35mya (his): 7 families
- 30mya: about 20 families
- 25mya: about 40 families
- 20mya: about 70 families
- Current: 144 families (IOC), 136 (H&M4)
Applying manageable chunk theory, I'd say a system using 20 mya and 70 families might be able to get some traction. Anything less and the Passeridae becomes too large to be a useful classification. There is also tradition. Halving the the number of families would get enough resistance, anything more and they'd be storming the citadel.