Ismael "El Mayo" Zambada, the notorious alleged co-founder of the Sinaloa Cartel, pleaded not guilty to U.S. drug charges on Friday after he and a son of a Mexican drug lord were arrested in Texas in a dramatic achievement for U.S. law enforcement that could usher in a seismic shift to Mexico's criminal landscape.

Court records showed that Zambada directed that a not guilty plea be entered on his behalf, which was accepted by U.S. Magistrate Judge Anne Berton.

At an initial court appearance in a Texas courtroom on Friday, Zambada, who is believed to be in his 70s and was in a wheelchair, was read his rights and charges, according to a transcript.