A mafi tsufa tsohuwar squirrel burbushi, Hesperopetes, ya koma zuwa Chadronian (karshen Eocene, kimanin shekaru 40-35 da suka wuce) kuma yana kama da squirrels masu tashi na zamani. Yawancin burbushin burbushin burbushin halittu, daga Eocene na ƙarshe zuwa Miocene, ba a sanya su da tabbaci ga kowane zuriya mai rai ba. Aƙalla wasu daga cikin waɗannan watakila sun kasance bambance-bambancen tsofaffin "protosuricles" (a ma'anar cewa ba su da cikakkiyar kewayon autapes na squirrels masu rai). Rarraba da rarraba irin waɗannan tsoffin kakannin da ke ba da shawara ga squirrels na iya samo asali a cikin rukuni na Arewacin Amurka.
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