family, Columbidae. The oldest known fossil of the genus is an isolated humerus (USNM 430960) known from the Lee Creek Mine in North Carolina in sediments belonging to the Yorktown Formation, dating to the Zanclean stage of the Pliocene, between 5.3 and 3.6 million years ago. Its closest living relatives were long thought to be the Zenaida doves, based on morphological grounds, particularly the physically similar mourning dove (now Z. macroura). It was even suggested that the mourning dove belonged to the genus Ectopistes and was listed as E. carolinensis by some authors, including Thomas Mayo Brewer. The passenger pigeon was supposedly descended from Zenaida pigeons that had adapted to the woodlands on the plains of central North America. The passenger pigeon differed from the species in the genus Zenaida in being larger, lacking a facial stripe, being sexually dimorphic, and having iridescent neck feathers and a smaller clutch. In a 2002 study by American geneticist Beth Shapiro et al., museum specimens of the passenger pigeon were included in an ancient DNA analysis for the first time (in a paper focusing mainly on the dodo), and it was found to be the sister taxon of the cuckoo-dove genus Macropygia. The Zenaida doves were instead shown to be related to the quail-doves of the genus Geotrygon and the Leptotila doves. A more extensive 2010 study instead showed that the passenger pigeon was most closely related to the New World Patagioenas pigeons, including the band-tailed pigeon (P. fasciata) of western North America, which are related to the Southeast Asian species in the genera Turacoena, Macropygia and Reinwardtoena. This clade is also related to the Columba and Streptopelia doves of the Old World (collectively termed the "typical pigeons and doves"). The authors of the study suggested that the ancestors of the passenger pigeon may have colonized the New World from South East Asia by flying across the Pacific Ocean, or perhaps across Beringia in the north. In a 2012 study, the nuclear DNA of the passenger pigeon was analyzed for the first time, and its relationship with the Patagioenas pigeon was confirmed. In contrast to the 2010 study, these authors suggested that their results could indicate that the ancestors of the passenger pigeon and its Old World relatives may have originated in the Neotropical region of the New World. The cladogram below follows the 2012 DNA study showing the position of the passenger