Momentum is calculated using the formula:
\[ \text{Momentum} (p) = \text{mass} (m) \times \text{velocity} (v) \]
Given that both dogs are running with the same velocity but one dog is twice as large (in mass) as the other, we can denote the mass of the smaller dog as \(m\) and the mass of the larger dog as \(2m\).
For the smaller dog: \[ p_{\text{small}} = m \times v \]
For the larger dog: \[ p_{\text{large}} = 2m \times v \]
This shows that the momentum of the larger dog is:
\[ p_{\text{large}} = 2(m \times v) = 2p_{\text{small}} \]
Therefore, the larger dog had twice the momentum of the smaller dog.
So, the correct statement is:
The larger dog had twice the momentum of the smaller dog.