Sorry if my question is a silly one. I wasn't even born when the first ever Simpsons episode was aired. I am watching them from the beginning but I'm wondering was there any shows before the S1E01 - "Simpsons Roasting on an Open Fire" ?

In the 138th special episode (`The Simpsons [7x10] The Simpson's 138th Show Spectacular`), it shows some clips they didn't air, which I can recall most of them. But the characters look much different so I'm not sure it was a parody or whether there was some shows prior to the first official episode. 

Sherlock had such episode. Can anyone remember if there was anything aired before the first episode? Also, that very first episode starts without any specific introduction to characters. Is it the norm?