Also from the NYC Taxicab Fact Book (page 23):
Until 1954, New York City required that taxicabs seat five passengers behind the driver and have a trunk-mounted luggage rack. Also required was a grill in the trunk to prevent carriage of dead bodies. Only Checker, Desoto and Packard had models that fulfilled the “jumbo” vehicle requirements. New York City allowed smaller vehicles in 1954, eventually leading to the demise of large vehicles.
(Lots of interesting and bizarre statistics in that publication!)