Here's why:
* Large: Capybaras are the largest rodents in the world, reaching up to 4 feet in length and weighing over 100 pounds.
* Almost Tailless: They have a very short, stubby tail that is barely noticeable.
Other possibilities:
While Capybaras are the most fitting description, there are a few other rodents that might fit your description depending on your definition of "almost tailless":
* Paca: There are two species of paca, both of which are large rodents with very short tails.
* Agouti: Agoutis also have relatively short tails compared to other rodents, but they are not as large as Capybaras.
Let me know if you have any other clues, and I can help you narrow it down further!