elta ▁is ▁the ▁oldest ▁nod osa ur id ▁from ▁Europe ; ▁it ▁is ▁derived ▁from ▁the ▁lower ▁Alb ian ▁Esc ucha ▁Form ation . ▁The ▁oldest ▁western ▁North ▁American ▁nod osa ur id ▁is ▁Sau rop elta , ▁from ▁the ▁lower ▁Alb ian ▁Little ▁She ep ▁M ud stone ▁Member ▁of ▁the ▁Clo ver ly ▁Form ation , ▁at ▁an ▁age ▁of ▁ 1 0 8 . 5 ± 0 . 2   mill ion ▁years . ▁Eastern ▁North ▁American ▁foss ils ▁seem ▁older . ▁Te eth ▁of ▁Pr icon odon ▁cr ass us ▁have ▁been ▁derived ▁from ▁the ▁A rund el ▁Clay ▁of ▁the ▁Pot om ac ▁Group ▁of ▁Maryland , ▁which ▁dates ▁near ▁the ▁A pt ian – Al bian ▁boundary . ▁A ▁Pro pan op l osa urus ▁h atch ling ▁was ▁un cover ed ▁from ▁the ▁base ▁of ▁the ▁underlying ▁Pat ux ent ▁Form ation , ▁dated ▁to ▁the ▁upper ▁A pt ian , ▁making ▁Pro pan op l osa urus ▁the ▁oldest ▁nod osa ur id . ▁Pol ac anth ids ▁are ▁known ▁from ▁pre - A pt ian ▁fa una ▁from ▁both ▁Europe ▁and ▁North ▁America . ▁The ▁timing ▁of ▁the ▁appearance ▁of ▁nod osa ur ids ▁on ▁both ▁contin ents ▁indicates ▁the ▁orig ins ▁of ▁the ▁cla de ▁preced ed ▁the ▁isol ation ▁of ▁North ▁America ▁and ▁Europe , ▁thereby ▁pushing ▁the ▁group ' s ▁date ▁of ▁evolution ▁back ▁to ▁at ▁least ▁the ▁middle ▁A pt ian . ▁The ▁separation ▁of ▁N od osa ur idae