Wednesday, December 06, 2006

 

Dinosaurs: Ancient Egg Cluster Preserved in Glass

The first fossils of half-billion-year-old clusters of soft-shelled eggs have been found preserved in a strange new way in south China - some of the eggs were even caught in the act of dividing.

The three-dimensional clusters of petrified eggs from invertebrate animals that lived in a sea 501 million to 510 million years ago are preserved in silica - glass essentially. Jih-Pai Lin, an Ohio State University (School of Earth Sciences) paleontologist, explained this is a totally unexpected way for soft eggs to fossilize and survive for eons.

Lin is the lead author of a report on the egg clusters published in the December issue of the journal Geology.

The discovery means there are probably even more early eggs and embryos fossilized in ancient rocks. Fossil hunters just need to keep in mind the different ways they might be preserved, and therefore the different types of rocks in which they might be found.

Continued at "Dinosaurs: Ancient Egg Cluster Preserved in Glass"
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Based on the Geology paper "Silicified egg clusters from a Middle Cambrian Burgess Shale-type deposit, Guizhou, south China"

Abstract:

Although knowledge of Cambrian fossil eggs and/or embryos has increased dramatically, embryos were previously unknown in siliciclastic settings of coeval strata. Here we report for the first time egg clusters in a fine-grained siliciclastic matrix from the Middle Cambrian Kaili Formation lagerstatte (513-501 Ma), south China. Some were imaged under synchrotron radiation. These spheroids are preferentially preserved as microcrystalline quartz and interpreted as marine invertebrate fossil eggs based on patterns of spheroid arrangement, shape, and analogues of fossil and modern invertebrate eggs. Embryos with cleavage cells are evident in at least one cluster. Detailed element analyses show that eggs are primarily preserved as solid silica replacement, and there is a calcite layer covering the eggs replacing the original organic layer. Silicification of intact invertebrate egg clusters is reported here as a new mode of preservation associated with a Burgess Shale*-type deposit.
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*Info on the Burgess Shale:

The Burgess Shale is a black shale fossil bed (Lagerstatte) named after Burgess Pass, close to where it was found, high up in the Canadian Rockies in Yoho National Park near the town of Field, British Columbia. Fossils were first found in the Burgess Shale in 1909 by Charles Doolittle Walcott (info), who returned in the following years to collect additional specimens. Walcott recognized the arthropod fossils were new and unique species, but careful reexaminations showed that many in fact constituted entire new phyla of life, and even today some have proven impossible to classify. The fossils are especially valuable because they include appendages and soft parts that are rarely preserved. [More] [Science and Paleontology]

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