▁was ▁first ▁noted ▁in ▁ 1 9 0 3 ▁and ▁again ▁in ▁ 1 9 3 6 . ▁ ▁Long - bone ▁hist ology ▁enables ▁research ers ▁to ▁estimate ▁the ▁age ▁that ▁a ▁specific ▁individual ▁reached . ▁A ▁study ▁by ▁Eva ▁Gr ie bel er ▁et al . ▁( 2 0 1 3 ) ▁exam ined ▁long - bone ▁hist ological ▁data ▁and ▁concluded ▁the ▁A pat osa urus ▁sp . S MA 0 0 1 4 ▁we ighed ▁, ▁reached ▁sexual ▁m atur ity ▁at ▁ 2 1 year s , ▁and ▁died ▁aged ▁ 2 8 . ▁The ▁same ▁growth ▁model ▁indicated ▁A pat osa urus ▁sp . BY U ▁ 6 0 1 – 1 7 3 2 8 ▁we ighed ▁, ▁reached ▁sexual ▁m atur ity ▁at ▁ 1 9 year s , ▁and ▁died ▁aged ▁ 3 1 . ▁ ▁Ju ven iles ▁Comp ared ▁with ▁most ▁sau rop ods , ▁a ▁relatively ▁large ▁amount ▁of ▁ju ven ile ▁material ▁is ▁known ▁from ▁A pat osa urus . ▁Multiple ▁spec im ens ▁in ▁the ▁O M N H ▁are ▁from ▁ju ven iles ▁of ▁an ▁und et erm ined ▁species ▁of ▁A pat osa urus ; ▁this ▁material ▁includes ▁partial ▁shoulder ▁and ▁pel vic ▁g ird les , ▁some ▁verte bra e , ▁and ▁lim b ▁b ones . ▁O M N H ▁ju ven ile ▁material ▁is ▁from ▁at ▁least ▁two ▁different ▁age ▁groups ▁and ▁based ▁on ▁over la pping ▁b ones ▁likely ▁comes ▁from ▁more ▁than