古生代psammichnitids(砂迹类)的行为习性演化及其生物古地理迁移*

Psammichnites和Dictyodora为古生代海相环境典型的弯曲带状遗迹,是由具有虹吸器官的生物所形成的遗迹化石,一般被归入到psammichnitids。通过文献资料调研和样品分析,对古生代Psammichnites和Dictyodora的形态功能对比和时空分布特征进行研究。结果表明: (1)Psammichnites通常具有短、浅的凹槽; 随着时间的推移,Dictyodora的壁高却逐渐增大。(2)Psammichnites主要分布于正常浅海环境; Dictyodora大都分布于深海环境,也有个别类型分布于浅海环境。(3)Psammichnites的种级多样性在石炭纪浅海环境呈快速增加,属于晚期辐射类型,但Psammichnites gigas广泛分布于寒武纪早期,具有很好的地层指示意义; Dictyodora的种级多样性在奥陶纪快速增加,属于早期辐射类型。(4)寒武纪—奥陶纪,Psammichnites和Dictyodora主要分布于南半球中高纬度的Iapetus和Rheic大洋,其中Laurussia大陆的形成以及Iapetus和Rheic大洋的闭合对其古地理分布具有显著影响; 自石炭纪开始,Psammichnites和Dictyodora均向新的空白生态位进行迁移,反映出造迹生物对于新生态位的适应和迁移均受环境变迁的强烈影响; 二叠纪之后,Psammichnites和Dictyodora在地层中没有发现,可能暗示它们的造迹生物均在二叠纪末生物大灭绝事件中遭受了毁灭性打击。上述对Psammichnites和Dictyodora行为习性演化特征及其生物古地理迁移特征的系统总结和归纳,可为从精细和精深角度深入解读遗迹化石所反映的遗迹类群的演化生态学和生物古地理迁移特征提供新资料和新认识。

Behavioural evolution pattern and biogeographical migration of the Paleozoic psammichnitids

Psammichnites and Dictyodora are grouped into psammichnitids,representing the typical slug-like bulldozers with a snorkel living in the marine environments during the Palaeozoic. Through the morphological and functional analysis of Paleozoic Psammichnites and Dictyodora,combining with their spatio-temporal distribution characteristics,it is found: (1)Psammichnites generally has short and shallow grooves,and the wall height of Dictyodora gradually increased with time. (2)Psammichnites is mainly distributed in the shallow-marine environment,whereas Dictyodora is mainly distributed in deep-marine environment with occasional occurrences of certain ichnospecies in the shallow-marine environment. (3)The ichnodiversity of Psammichnites ichnospecies rapidly increased in the Carboniferous shallow-marine environment,belonging to the top-heavy pattern. Psammichnites gigas is distributed widely in the Early Cambrian strata,which is of biostratigraphic importance. The ichnodiversity of Dictyodora ichnospecies rapidly expanded in the Ordovician,representing the bottom-heavy pattern. (4)Psammichnites and Dictyodora were mainly distributed in the Iapetus and Rheic oceans in the middle and high latitudes of the southern hemisphere during the Cambrian to Ordovician. Due to the formation of Laurussia and the closure of Iapetus and Rheic oceans,Psammichnites and Dictyodora migrated to the new empty ecological niches from the Carboniferous to Permian,indicating that the adaptation and migration of trace makers to new ecological niches might be strongly influenced by environmental changes. Until now Psammichnites and Dictyodora have not been found in the post-Permian strata,possibly suggesting that their trace markers went extinct in the end-Permian mass extinction. On the basis of the above systematic summary and induction of the behavior habits,biogeographic migration characteristics and evolutionary characteristics of Psammochnites and Dictyodora,it can provide new data and new understanding of the evolutionary ecology and biogeographic migration characteristics of trace groups reflected by trace fossils from a detailed and profound perspective.