an animal is a kind of organism & a horse is a kind of animal ->  a horse is a kind of organism  a horse is a kind of organism & if fossils of an organism change depending on the level in which they were found then that species of organism changed over time ->  if fossils of horses change depending on the level in which they were found, then the horses has changed over time  the fossils of horse has shorter bones in lower levels and the fossils of horse has longer bones in the upper level & younger layer of rocks are on top of the older layer of rocks according to superposition ->  the younger fossils of horse has longer bones than the older fossils of horse  if fossils of horses change depending on the level in which they were found, then the horses has changed over time & the younger fossils of horse has longer bones than the older fossils of horse -> horse species have changed from smaller to larger over time