Changes involve the arrangement and complexity of septa in the mature conch and in its shape, ending with the more elongate and compressed mature " Ascoceras ".
2.
A phylogenetic sequence can be seen in the Ascoceratidae, from " Probillingsites " through " Schucertoceras ", then " Billingsites ", in the Upper Ordovician, and finally to the middle and upper Silurian " Ascoceras ".
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