smaug

[Orophin]

I am pretty sure that there is an instance in the Hobbit where it is stated that there are more dragon in the mountains of the north and that Smaug is simply the biggest of them. I do not think that he was the last one.

[Firefoot]

But there were dragons in the wastes beyond; and after many years they became strong again and multiplied, and they made war on the Dwarves and plundered their works.

So the rumour of the wealth of Erebor spread abroad and reached the ears of the dragons, and at last Smaug the Golden, greatest of the dragons of his day, rose and without warning came against King Thrór and descended on the Mountain in flames.

Both quotes are from Appendix A, Durin's Folk. Therefore, Smaug was not the last Dragon, but the last great dragon and the greatest of the time.

[Gothbogg the Ripper]

I reckon he was the last Dragon, if he (or another dragon) were known to still exist then they might have actually tried to get the Dragon to melt it but I'm not sure.

I seem to remember that Scatha was still around at the time of 'the hobbit', up in the withered heath. Wouldn't she count as a great dragon? Or is it that Smaug was the last winged dragon?