When Avis Budget Group announced it would be acquiring car-sharing service Zipcar earlier this year, the company said it expected key members of the Zipcar team to stay on to run the service — but Zipcar's CEO Scott Griffith won't be one of them. Fortune reports that the Griffith has stepped down from the company, just a day after Avis formally completed its acquisition. Taking his place will be Zipcar's chief operating officer Mark Norman.

In a letter to Zipcar employees today, Griffith writes that "Zipcar will require a fully-committed leader to unlock the power of the merger," and that "it's best if I step back and give someone else the opportunity to put the pedal down and take Zipcar to the next level." The Boston Globe's Scott Kirsner first broke the news on Twitter — and as of this writing, there is still no formal press release on Zipcar's site announcing the change.

"I will remain Zipcar's biggest fan."

Griffith was a 10-year veteran of the company, and oversaw Zipcar's growth from a small start-up into the kind of multi-national company that could warrant that $500 million that Avis paid for it. Griffith gives the requisite pep talk in his farewell letter, writing that he believes the company's best days are ahead and that "I will remain Zipcar's biggest fan." Still, it's hard to not see the transition as a sign that Griffith's focus on creating a disruptive service that decreases dependence on automobiles — and traditional car rentals in general — may not be something that is shared by Zipcar's new owner.