I always remember kobolds being described as rat-dog type guys. The David A. Trampier illustrations certainly looked reptillian, and I believe 1st ed MM entry mentioned eggs, but that is the only place I rember seeing kobolds as reptiles before 3rd edition. Having them be scaly, egg-laying rat-dog type guys works as well for me as any other. I did like the idea presented in earlier threads that they are egg-laying mamals (or near-mamals) like the platypus (now just give them a bill and poisonous spurs on their feet). Of course, the modern classification system for animals has existed for a relatively short time, so kobold (or anyone) need not even fit into any rational classification system; just let the rangers know what favored enemy they are covered by.