Homologous Traits
Koalas
and kangaroos each are two different species that possess a pouch for their
precocious young.
The
pouches of each species are used for keeping their premature offspring for
further development beyond the womb. The kangaroo’s pouch differs from koala
pouches in that kangaroo pouches open horizontally on the front of the body,
while a koala’s pouch opens backwards and down, it also has a sphincter that
keeps the young from falling out. Both of the species pouches are sticky,
however, the kangaroo will lick their pouch clean, unlike koala pouches which
have a self-cleaning system. The differences in the pouches between the two
species developed due to the differences in environment and lifestyles. The
koala’s pouch would not work well for kangaroo because the young would fall out
very easily, and the front horizontal pouch would not work well for koalas since
they climb trees and the young would also fall out.
The
earliest known common ancestor of kangaroos and koalas has been identified as Hypsiprymnodon bartholomaii. Not much is known about marsupial ancestors,
but it is believed that the evolution of their pouches evolved due to
competition with placental mammals.
Analogous Traits
Dolphins
and goldfish both possess a dorsal fin. A dorsal fin is a fin located on the
backs of marine and freshwater animals.
In
each species the fin is used to help navigate through water. The fin stabilizes
the body and keeps it from rolling over in water. The dorsal fin also assists
in sudden turns. Each species developed fins as an adaptation to living in
water environments.
Going
back to 405 million years ago, sea mammals and fish evolved from a common
ancestor from the group Osteichthyes. Osteichthyes
did, and still possess fins.
