( ( ( Two characteristics ) ( of ( mammals ( that ( ( are ( at least ) ) ( sometimes ( preserved ( in ( the ( fossil record ) ) ) ) ) ) ) ) ) ) ( ( are ( ( ( -LRB- ( 1 -RRB- ) ) ( the ( mammalian ( middle ear ) ) ) ) ( contains ( ( a chain ) ( of ( ( ( ( ( ( ( ( three bones ) , ) ( the malleus ) ) , ) incus ) , ) and ) stapes ) ) ) ) ) ) ; ) )
(ROOT (S (NP (NP (CD Two) (NNS characteristics)) (PP (IN of) (NP (NP (NNS mammals)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (ADVP (IN at) (JJS least)) (VP (ADVP (RB sometimes)) (VBN preserved) (PP (IN in) (NP (DT the) (JJ fossil) (NN record)))))))))) (VP (VBP are) (NP (NP (LST (-LRB- -LRB-) (LS 1) (-RRB- -RRB-)) (DT the) (JJ mammalian) (NN middle) (NN ear)) (SBAR (S (VP (VBZ contains) (NP (NP (DT a) (NN chain)) (PP (IN of) (NP (NP (CD three) (NNS bones)) (, ,) (NP (DT the) (NNS malleus)) (, ,) (NP (NNS incus)) (, ,) (CC and) (NP (NNS stapes)))))))))) (: ;)))
Two characteristics of mammals that are at least sometimes preserved in the fossil record are (1) the mammalian middle ear contains a chain of three bones, the malleus, incus, and stapes;
(ROOT (S (NP (DT The) (JJ mammalian) (JJ middle) (NN ear)) (VP (VBZ has) (NP (CD three) (NNS bones))) (. .)))