Complex sentence: The species was regarded to be extinct, until Reinhardt confirmed it was alive while describing a large pod at the Kiel Bay in 1861, one of which could be captured, whereas some others were found, the following year, beached on the coast of Denmark.
Split into simpler sentences: The species was thought extinct until Reinhardt confirmed it was alive when he described a large pod at the Kiel Bay in 1861. One of these was captured, and others were found the following year, beached on the coast of Denmark.