MINIATURIZATIONS OF SILICEOUS SPONGE SPICULES DURING THE PERMIAN-TRIASSIC CRISIS IN SOUTH CHINA

Urbanek (1993) first found the “Lilliput effect” with Late Silurian graptolites and many paleontologists have also discovered that this phenomenon occurred in the biggest five mass extinction in Phanerozoic era. Body size is a key morphological variable, with implications for many aspects of an animal’s biology, behaviour, and ecology (Twitchett, 2007). It may be important to understand the “Lilliput effect” to find the causes of ecological, environmental, and biological changes, such as the sea level change, anoxic, low productivity during biotic mass crisis.

The end-Permian mass extinction is the largest event among the “Big Five” during the Phanerozoic history in terms of the severity of taxonomic diversity losses (Sepkoski, 1981; Erwin, 1994). During the mass extinction, bivalves,gastropod, brachiopods, conodonts, and trace fossils were clearly miniaturized in species or genera. However, it is less researched about the porifera which widely distributed and lastly appeared in geologic history.

Researching spongy spicule size is importance to understand how the paleoenvironment change during the end-Permian. Four common forms of the spongy spicule from the Changhsingian and Lowermost Triassic in Dongpan Section, South China are assessed in the size variation for discussing the cause of miniaturization during the Permian-Triassic mass extinction. The result shows that the siliceous spongy spicules reduced 40%-50% in size. The reductions in body size were synchronously occurred with the mass extinction and diversity decrease. The reductions of size are well explained with anoxic condition and low productivity in the lower part of the section, corresponding to the middle Neogondolella yini Zone. The paleoproductivity collapse could be adopted for explaining the cause of the “Lilliput effect” near the Permian-Triassic boundary in the studied section. , corresponding to the upper Neogondolella yini Zone and upwards.