There are several examples that prove common ancestory (something creationists don't generally believe in) and this is simply the idea that different animals share the same common origin so for example all dogs and all cats share a common ancestor.

Creationists have a bit of a probem though when evolutionary science predicts and proves parts of macroevolution.

Example 1: Endogenous retroiviruses.

Endogenous retroviruses are molecular remnants of a past parasitic viral infection. Basically what happens is that a virus leaves some of its Genetic material (DNA) inside the genome of the animal infected. This bit of genetic code becomes part of that animals genome (its own genetic code) and is passed on - especially if it is an egg or sperm cell.

Us Humans can have as much as 1% of our genome made up of these old viruses. This means we are carrying around about 30,000+ of these old virus artifacts. As this genetic material is passed on for many years it can provide a clear line of descent.

Guess which other animals share the same virus sequences as us?

From Monkeys to Humans we all have the same Virus DNA
The attached pictures shows how particular virus (HERV-K) code has been found in several primates from Monkeys to Humans. This is strong evidence for a common ancestry as the genetic material is the same after being passed on from the original infection.