I think all reptiles are capable of feeling to some extent "basic emotions"
But I believe more "complex" emotions are restricted to those higher mammals, birds and perhaps those species that evolved to live in complex social structures.
I have probed a lot of questions about this in the past as I do find the concept interesting. In my experience I have seen some "strange" behavior in some of the animals I have cohabited, these species are notably well known to be solitary in the wild with the exception for mating seasons, but none of the behaviors I simply have not seen any of this "dominant" behavior people go on about in any of my cohabitation. My bearded dragons for example (both female) were housed together in a standard 4x2x2 (while some argue this space dimension is too small for two, I never seen them compete over anything, but instead shared the basking point at differing points of the day. I found that interesting, furthermore even on hot warm summer days when I had them outside in the garden, outdoor enclosure, and even in the orchid, they rarely ever ventured far from each other and had all the space in the world to escape each other, I never seen it.
I am not suggesting that it was anything like love, affection or any such thing, but I do beleive from my observations it was a bit more complicated than just simply saying yes, to this, and no to that.
Then you look at animals like iguanas, these animals actually are social and is otherwise well documented, for a reptile this is unusual, even at times of the year when they are not in season, most people I converse with out there, or have been out there and even in some cases have these guys living on there doorsteps tell me you will never see (and have had videos sent to me) iguanas alone in ONE tree. The social structures are a little more complex than this, each mating territory can have one dominant male, and five females within it, but each tree can have multiples of these "structures". The work by G Burghartd and Stan Rand in the excellent book iguanas of the world is very interesting and well worth a read.
Then you look at E. R Jacobsons book, Iguanas Biology, husbandry and medicine 2003 which is a further more real eye opener into iguana social behavior, right from being young right into adult hood. To further complicate this issue there survival strategies are not altogether black or white either and may be determined by other factors, some choose a solitary life style, others not so much so, others will (such as pseudofemales) infiltrate other territories disguised as females and may or may not attempt to pass on his genes by gripping one of that territories females before moving on.
I do know in my experience that reptiles can come to learn and tolerate our presence, with good routine and conditioning or "taming" they can come to see us as a none threat. 98% of the iguanas I have had will climb out right onto my arm themselves when this is continued, it varies from individual to individual when they reach that stage but most do. I can't ever recall any time I have had to grab a specimen other than for moving to A-B like the outdoor enclosure, or for medicating or a vet visit.
On the other hand though, it could equally be just as much argued that humans are much less well equipped to deal with emotions, as our emotions cause us to do all kinds of strange and psychotic things.
I personally do not beleive they are capable of feeling "complex" emotions like love, but you look at some of the behavior of cyclura iguanas, and tell me there isn't something else there, some run right up to there owners like dogs, and may even learn there own names.
At the same time we should be careful not to confuse.
Intelligence, emotion, and communication for the same thing.
It is a very interesting discussion to have though, and one that shouldn't ever get boring, we shouldn't be so quick to dismiss reptile emotion, it might not be on the same level of the phenomenon we associate emotion with, but I am not convinced with (some species I have kept in differing settings) that there is completely nothing, but I wouldn't either be prepared to say it was in the range of the more complex emotions we associate.
I mean, does a monitor lizard feel guilty after killing its prey? would it feel guilty if it nailed it's owner?
Are they capable of feeling "affection"? or do we just apply abstract thoughts to those behaviors with our big human brains because we would see that behavior the animal is showing in the way we would?
Is it all more complicated than just saying (solitary means they don't feel anything)?
Just some thoughts for a discussion I have an interest in.
I am of mixed views and it is generally species specific, I don't think reptiles can all be generalized as the same, but I could be wrong.