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Besides sharks, primitive skates, chiemaeras and crossopterygians (’tassel-fins'), there are especially frequent finds of ganoids. This Weigert
reproduction shows a member of the so-called ganoid fishes. The ganoids had already reached their evolutionary climax in the Permian and Triassic, some 270 – 190 million years ago; today they are few in number when compared
with the dominant bony fishes.
The internal skeleton of the ganoid fishes, especially the vertebral column, is only lightly ossified. The massive scales covering the entire body are
usually rhomboidal with a glossy surface of ganoin. Lepidotus belongs to the pycnodonts, a name which means ’densely packed teeth’; its jaws and palate were covered with hemispherical crushing teeth arranged like cobbles in a
pavement. This is indicative of a hard diet, consisting of such items as bivalves and gastropods which were simply ground down. The enclosing layers o f sea-mud, subjected to increasing pressure, dehydration and mineralisation,
finally hardened into limestone, the skeleton embedded therein being compressed into a paperthin layer. Only 150 million years later was the fossil brought to light by a quarry worker and fully exposed through the patience and
skill of a preparator.
Original: Jura-Museum, Willibaldsburg, Eichstätt/Bavaria, Germany
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