IAH=PHX last week had a small dog in a carrier with the couple in !A and !B. The couple was not happy that the FA wouldn't let them sit in Row 1 with a carrier because they, "always sit in these seats with the dog". After much back and forth complaining with the FA repeatedly saying "I'm sorry my coworkers on other flights did not follow the rules", the couple got two people in row 2 to swap.

The was an awfully playful, friendly, and rambunctious 40-ish pound dog in coach with a vest and accessories, so I'm assuming a service animal despite the rambunctiousness. I was behind the human and dog leaving the airport as the human said to friends it was tough in a middle seat. One person sitting next to her was "great" but the other was "cranky" the entire flight. I'm a fan of dogs, but I'd probably be cranky too if the middle seat next to me also included an overly friendly 40 lbs. dog trying to squeeze in at our feet. Thinking back, I can only recall largish service animals in the bulkhead in coach.