Yes they do and I don't literally think it's about jealousy, I believe it's more about the dog's natural territorial behavior. Dog's are very territorial in nature and very protected to their keen as well. Specially when your dog lacks more interactions with other dogs or people, the tendency is they might attack anything or anyone that is new to them. In my case there was this incident involving my two years old chocolate brown Dachshund and my 3 mothns old German Shepherd. I believe my Dachshund was still two years old at that time when I both a 3 month old German Shepherd. My mom put them both on our couch while she was watching TV with them. Then suddenly to my mom's surprise my Dachshund deliberately pushes my 3 month old German Shepherd off the couch. My German Shepherd fell down and literally injured both of his back foot leaving him cripple. But luckily, after a long months of therapy my German Shepherd can walk again. The lesson I learned from this experience is do not leave your new puppy with your old jealous dog alone.

According to my research the dog are getting jealous. One of the example I saw is when you got a new baby born. You should let the dog see him for the dog to welcome the new family member and he will also protect the baby <3

Yes, for me I think dogs do get jealous too because they also have feelings. And when you have a dog they will treat you as their own family, that is why when you try to put your attention on others they will try to get your attention back to them. Because they can also feel neglection and they are also very territorial and will try to act wildly if they feel like someone is invading their space.

My dog used to get jealous all the time if another dog was around! She made it known that I was her owner and she was my dog. I had to be careful when we went for walks so she wouldn't get mad at other dogs who wanted me to pet them. She had to give the approval first. 

Of course yes, dogs do feel jealous especially when they are more than one or you have another pet that's not a dog. My dogs are big attention seekers. Once I carry one or pet one, the rest would want the same thing. It's a complete tussle for me with all of them. 

Both of my dogs are always jealous when I carry one and doesn't the other. He will keep a very mean face and even bark at me. But they feel very comfortable when I carry both of them. 

Dogs can feel jealousy and even sad, my aunt had a dog but decided to get a cat as well and when the cat was brought how the dog would try to receive all attention at all times but as time went on the two got along.

Even my cats are always very jealous whenever I carry one of them and leave the others without carrying them at the same time. It's also equivalent to my dogs as well because they're always seeking my attention all the time and I try as much as I can to provide it for them. 

I have only one dog, so there's no other pet that's going to make him feel jealous. It's a very common thing in pets to feel jealous when they are sharing your attention. 

This is very common in dogs and it is more of a territorial thing rather than jealousy. Much like with most animals they protect what is theirs and it can sometimes be perceived as jealousy even though it is not.

I wouldn't worry too much if they get like that and instead, reassure them that everything is okay. 

I believe that all animals which human beings keep as pets usually feel jealousy every now and then depending on how you are showing them attention. They don't usually like to share unless you started training them from when they were small together to share attention.