- 期刊
- OpenAccess
THE CAMBRIAN LOBOPODIAN MICRODICTYON SINICUM
寒武紀葉足動物Microdictyon sinicum
摘要
Microdictyon was a soft-bodied onychophoran-like animal, forming a significant component in many Early Cambrian faunas. It was for long known only from disarticulated, mineralized plates. The discovery of the first complete specimens of Microdictyon (Chen et al. 1989) unexpectedly showed that such plates attached to the trunk sides of a caterpillar-like animal. About 70 new specimens recently collected permit a detailed and more comprehensive description of Microdictyon sinicum than could be accomplished in the original paper. Homology analyses favor a reinterpretation of Microdictyon sincium, with a reversal of the first suggested anteroposterior orientation. In the new reconstruction, this animal had a long, weakly tapering anterior extension (head) with a terminal mouth, and an annulated subcylindrical trunk which was supported on ten pairs of annulated legs bearing paired claws; posteriorly was a short anal extension. Along its flanks, there were nine pairs of tough, possibly mineralized plates. The presence in many specimens of double sets of plates, with one set 13-20% larger than the other, shows that before molting the new plates were formed beneath the old ones. Small Microdictyon specimens are usually in direct association with Eldonia, a pelagic animal, which indicates a pseudopelagic life style in juveniles. Closest affinity of this unusual animal lies with the celebrated Hallucigenia and other armoured lobopodians, together forming a group closely allied with the Recent Onychophora. The relationships between the two groups are left undetermined pending a detailed phylogenetic analysis.
並列摘要
微網蟲是寒武紀早期動物群的重要成員，與現生有爪類的造型十分相似。微網蟲早就以其造型十分奇特的骨片出現於科學文獻。一直到1989年，由於微網蟲完整化石的發現，人們才非常意外地認識到這些骨片竟然是長在毛蟲狀生物身軀的兩側。自1989年以來，又陸續發現了70多塊完好的化石標本，這些發現為深入了解微網蟲解剖學的特徵提供了可能。根據同源比較分析，本文對微網蟲前後定向重新進行了解釋。據新的解釋，微網蟲具有細長的頭部，口在頭的終端；身軀次圓柱狀，表面具橫紋，有10對帶爪的腿；腿的表面具橫紋。軀幹兩側嵌有9對堅硬的骨片，這些骨片有時呈雙疊狀，新形成的骨片比未脫落的骨片約大13-20%。小型微網蟲常與Eldonia（已滅絕浮游生物）在一起，表明微網蟲幼年期營假浮游生活方式。微網蟲與富有盛名的Hallucigenia，以及其他寒武紀葉足類構成具有親密演化關係的共源類群，至於這一類群與現生有爪類的演化關係，本文暫作懸案。