The first group consists of the facts of palæontology, or the fossil record of past animal life.
The fossil record of the kangaroo rats is so scanty that one can but speculate on the evolutionary sequence.
This is especially necessary in the early part of our ancestral tree, because the fossil record quite fails us.
Any fossil record of Kinosternon is a welcome find, and these two specimens give new data both as to age and distribution.
The fossil record is too incomplete to reveal the time when the two tribes diverged.