What process allows for the relatively complete preservation of Xenacanthus remains in certain deposits?

Slow drying or anoxia in water bodies

The preservation quality of Xenacanthus fossils, often found relatively complete, points toward specific environmental catastrophes or slow changes in their habitat. This completeness suggests periods where the water bodies they inhabited either dried up slowly or experienced conditions of anoxia, meaning severely depleted oxygen levels. These conditions frequently lead to mass mortality events among aquatic populations because they cannot escape. Such events greatly favor rapid burial and fossilization before decomposition or scavenging can break down the delicate skeletal structures, such as teeth and spines, allowing for a more complete record to survive into the modern geological record.