Dogs

Dogs (Canis lupus familiaris, or Canis familiaris) are a race of semi-sentient mammals native to Earth. Dogs, while commonly feral in wildlife, are the most wildly domesticated fauna on the planet, with humans frequently adopting them as pets and domestic companions.

History
During the time Bruce Banner was living in Rio de Janeiro, he had a dog living with him. After General Ross discovered Banner's location and sends a team to capture him,  Banner escapes, leaving his dog behind.

Dogs, cats, and birds were sold in a Puente Antiguo pet store that Thor entered, looking for a horse. Kyle let Thor know that he couldn't get a horse there.

A dog was the only companion of a young Grant Ward when he was taken from a prison in Massachusetts to the wilderness of Wyoming by John Garrett to learn self-reliance. Six months later, Ward had named the dog Buddy and the two had become close.

Garrett, in order to teach Ward emotional detachment to become a HYDRA sleeper within S.H.I.E.L.D., ordered him to kill the dog before they could go to S.H.I.E.L.D. Academy. However, Ward was unable to kill Buddy, and instead he fired his gun to the air and allowed Buddy to run away into the woods.

A dog named Cosmo was one of the exhibits in the Collector's Museum. He survived the place's near-destruction and showed his loyalty to Tivan, despite Howard the Duck's disapproval.