山东郯城以蜥脚类恐龙为主的足迹化石群:古生态学及地层学意义

A sauropod-dominated ichnofauna from Tancheng County,Shandong Province:Implications for paleoecology and stratigraphy

在山东郯城县清泉寺附近发现一个以蜥脚类恐龙足迹为主的大型化石点。化石分布在4层连续层面上,足迹数量达200多个,但较清晰的主要分布在第2层面上,有71个,多呈椭圆形,其中最大的103cm,最小的13cm。尽管足迹总体较为杂乱,大小差别很大,风化剥蚀严重,但仍可识别出至少6条行迹。推测这6条形迹中的5条为蜥脚类,另一条为鸟脚类。中间的3条(Tw3～5)大致平行、行迹方向相似(NNE),足迹大小相似(长度平均值分别为75、74、71cm),行迹较为紧密(行迹中线间距离最宽处约1.7m),应为同时、并排行进的3个成年个体形成。特别令人瞩目的是,在行迹Tw4的中间,夹杂分布着至少12个小型椭圆形足迹,长轴直径13～21cm,有的足迹踩在大足迹之上,推测至少为2个跟随父母行进的幼年个体的行迹。边缘的3条行迹(Tw1、Tw2和Tw6)方向相反,应为随后的恐龙所遗留。通过恐龙行迹特征的研究,提供了蜥脚类恐龙群居的新证据。传统认为,该足迹点的产出层位为早白垩世大盛群最顶部的孟疃组,但根据足迹化石的产出特征及组合特点,结合含恐龙足迹层位的区域对比,认为清泉寺地区产恐龙足迹的这套地层应属于大盛群田家楼组。

A large sauropod-dominated tracksite was discovered in the neighborhood of Qingquansi in Tancheng County of Shandong Province,China.More than 200 dinosaur tracks have been identified from four continuous strata and 71 more distinctive tracks have been identified from the second stratum.Most of the tracks are in the shape of ovals,with the largest being 103 cm and the smallest 13 cm.Despite their overall disarray,size difference,severe weathering and corrosion,at least 6 trackways have been recognized,of which 5 are supposed to be sauropods and 1 to be ornithopod.The three middle sauropod trackways(numbered Tw3-5)might be left by three adult dinosaurs because they have similar track sizes(average track length 75,74 and 71 cm respectively),paralleling each other and proceeding in the same direction(NNE),and closely proceeding(the longest distance between trackways being only about 1.7 m).A more interesting phenomenon is that at least 12 small-sized elliptical tracks(13-21 cm long)are regularly distributed along the trackway Tw4,and noticeably some of the small tracks stepping onto the large ones,which implies that the track-makers of the small-sized tracks are at least two baby dinosaurs.The other three trackways proceed in opposite directions(SSW)and may be registered by subsequent dinosaurs.This research provides strong trackway evidence for the gregarious behavior among sauropods.The track-bearing strata have traditionally been believed to be the Mengtuan Formation,the upper-most beds of the Early Cretaceous Dasheng Group.Based on ichnoassemblages,the track-bearing strata features,and regional comparison of track-bearing strata,it is believed that the track-bearing strata in the Qingquansi area should be the Tianjialou Formation of the Dasheng Group.