Solution-Groups of related organisms

The evolutionary pathways of some groups of related organisms seem to have moved from larger to smaller organisms over time, such as the glyptodont to the armadillo, the mammoth to the elephant. Yet other groups of related organisms have exhibited a trend of increased sizes of species over time, such as the tine eohippus to the horse. Explain how this can occur.

"Is this question part of your assignment? We can help"