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A Rare Fossil Record
The preservation of embryos and juveniles is a rate occurrence in thefossil record. The tiny, delicate skeletons are usually scattered byscavengers or destroyed by weathering before they can be fossilized.
Ichthyosaurs had a higher chance of being preserved than did terrestrial creatures because, as marine animals, theytended to live in environments less subject to erosion. Still, their fossilizationrequired a suite of factors: a slow rate of decay of soft tissues, little scavenging by other animals, a lack of swiftcurrents and waves to jumble and carry away small bones, and fairly rapid burial. Given these factors, some areas have become a treasury of well-preserved ichthyosaurfossils.
The deposits at Holzmaden, Germany, present an interesting case for analysis. Theichthyosaur remains are found in black, bituminous marine shales depositedabout 190 million years ago. Over the years, thousands of specimensof marine reptiles, fish and invertebrates have been recovered from theserocks. The quality of preservation is outstanding, but what is evenmore impressive is the number of ichthyosaur fossils containing preserved embryos.
Ichthyosaurswith embryos have been reported from 6 different levels of the shale in a smallarea around Holzmaden, suggesting that a specific site was used bylarge numbers of ichthyosaurs repeatedly over time. The embryos are quiteadvanced i...