摘要
前言早寒武世海绵在文献中虽屡有报道(Rigby, 1976, 1986),但多为分散式保存的骨针,关于海绵骨骼整体化石的报道则极鲜见(Walcott,1886, 1889; Rigby, 1987)。云南澄江是世界上迄今所发现的保存大量完整海绵骨骼化石和层位最低的唯一产地。澄江海绵化石群的研究为重建海绵类早期历史提供了新的较可靠的科学依据。长期以来人们根据早寒武世地层中所发现的大量海绵骨针均为四射类型的事实,推测这一时期的海绵分异度低,主要由六射海绵少数分子所组成,普通海绵极稀少,还未得到发展(Rigby,1976,1986)。澄江海绵化石群的研究所得出的结论与以上的推测恰恰相反,实际上,早寒武世筇竹寺期的海绵在演化上已达到了一个新的高度,普通海绵已高度分异并成为海绵类中最主要的优势生物类型。在分异度、物种结构、骨骼结构方式和复杂程度等方面均表现了筇竹寺期海绵动物群与中寒武世布尔吉斯海绵动物群具有惊人的相似性;这些相似性表明,海绵动物在早寒武世早期(筇竹寺期)已达到演化上的第一高峰,在其后筇竹寺期到布尔吉斯期将近3千万年的地质历程中处于缓慢的渐进式进化过程。
Although isolated spicules of sponges are known, virtually in all continents with greatly abundant Lower Cambrian rocks, the preservation of verified articulate skeletons is extremely rare in the past records. The Chengjiang Lagerst(?)tten is of special importance in fossil sponge studies for the record of its older age and the excellent preservation. Becaause of the biased preservation, the knowledge of Lower Cambrian sponges has been heavily dependent on the isolated spicules which are largely known as isolated stauractines, and which have led to assumption by various authors that sponges in Early Cambrian had a limited diversity, consisting largely of Hexactinellid protosponges with a few rare demosponges. On the contrary, a supported evidence from the Chengjiang Lagerst(?)tten suggests that the sponges, particularly Demospongea in the Early Cambrian Chiungchussu stage underwent very rapid diversification which led to many indefinite morphologic types, with an evolutionary complexity which might stand comparison with those of the Middle Cambrian Burgess Shale. The striking similarity of the sponge fauna between the Chengjiang Lagerst(?)tten and the Burgess Shale suggests that sponges have retarded their evolutionary pace from the Chiungchussu stage for at least a period of 30 Ma.
Among the demosponges, Leptomitus has a simple and thin double-layered skeleton and stratigraphically lowest occurrence which have led to assumption as the central stock of the Demospongea. Fossil evidences indicate that many elements of demosponges have adopted from Leptomitus a virtually unchanged pattern of double-layered skeleton. None of multiple-layered skeletons have been known among the Cambrian sponges apart from the present new genus Quadrolaminiella. This new form is characterized by a unique four-layered and double-netted skeleton. The outer net consists of the 1st (outermost) and 2nd layers of oxeas, which extend parallel and vertical to the length of the sponges respectively; inner net formed by the 3rd and 4th
出处
《古生物学报》
CAS
CSCD
北大核心
1990年第4期402-414,507-512,共13页
Acta Palaeontologica Sinica
