Misikella

Misikella is an extinct group of small, ancient sea creatures called conodonts. Scientists first described two types of Misikella in 1974. One type is called Misikella longidentata, and the other is called Misikella posthernsteini. Most Misikella species lived during a time called the Norian-Rhaetian, and they had a special arrangement of their body parts called a bimembrate conodont apparatus. However, M. longidentata lived a bit earlier, during the Carnian-Norian time, and had a different arrangement called a tetramembrate apparatus.

Later, some scientists decided to keep the name Misikella only for M. longidentata and moved the other species to a new group called Axiothea. But many other experts still use the name Misikella mainly for M. posthernsteini and other species with the bimembrate arrangement. Interestingly, M. posthernsteini has been found in rocks from Japan that are very old, from a time called the Hettangian. This shows that after many conodonts disappeared, some may have survived for a while before being replaced by other sea creatures.

Use in stratigraphy

The top of the Norian, which marks the start of the Rhaetian in the Upper Triassic period, is close to when several species of Misikella first appeared, along with Epigondolella mosheri. In 2010, scientists defined the boundary between the Norian and Rhaetian periods by the first appearance of Misikella posthernsteini.

The main places being studied for defining this boundary are Steinbergkogel in Austria and Pignola-Abriola in Italy.