浙江天台中新统润楠属化石及其古环境指示

Machilus Fossil from Miocene in Tiantai,Zhejiang Province,China,and Its Paleoenvironmental Implications

对浙江天台中新统下南山组6块叶片压型化石——天台润楠Machilus tiantaiensis Ding S.T.et Sun B.N.sp.nov.,并对其叶结构和表皮构造特征进行了详细的研究.其主要特征为:叶椭圆形,全缘,顶端渐尖,基部楔形,侧脉羽状;表皮细胞垂周壁浅波状,单细胞毛基多集中于脉络区;气孔下生式,气孔器短平列型,副卫细胞1～2个.通过与现生植物进行对比分析,发现当前标本的叶结构和表皮构造特征与樟科润楠属(Machilus)十分一致.利用PAST(palaeontological statistics)软件对我国润楠属68种植物叶片的形态特征进行聚类分析,结果表明当前化石与M.pingii Cheng ex Yang最为接近;角质层分析也表明二者的表皮构造最为相似.利用化石与其现存最近亲缘种M.pingii的气孔比率,恢复了天台晚中新世的古大气CO2体积分数为407.9×10-6.此外,依据现生润楠属主要分布于亚洲东南部和南部的热带、亚热带地区,推断天台地区中新世的古气候较为温暖湿润.

Six fossil leaves with fine venation and well-preserved cuticles of Machilus tiantaiensis Ding S.T.et Sun B.N.sp.nov.（Lauraceae） were discovered from the Late Miocene Xiananshan Formation of Tiantai County,eastern Zhejiang Province,China.The fossils were characterized by elliptic shape with entire margin,acuminate apex,cuneate base and pinnate venation;the anticlinal walls of epidermal cells are undulated,the unicellular trichome bases are mostly found on the veins;leaves hypostomatic,stomata paracytic with two embedded guard cells and one or two subsidiary cells.The leaf cuticular and architectural features of these fossil leaves suggest the affinity within the genus Machilus.The quantitative traits of leaf morphology were studied here,and a free data analysis package（palaeontological statistics） is utilized for cluster analysis.The leaf morphologic and cuticular features show that the fossil is similar to the modern leaves of M.pingii mostly.The paleoatmospheric CO2 concentration is estimated through the stomatal ratio between the fossil species and the extant M.pingii Cheng ex Yang（nearest living relative of the fossil species）,and the result shows that the level of atmospheric CO2 in the Late Miocene of Tiantai is about 407.9×10-6.The modern trees of Machilus are distributed in tropical and subtropical regions of South and Southeast Asia,which indicates that the Miocene climate of eastern China was warm and humid.