Russian Asaphus Trilobite Evolutionary Sequence:

Selective pressures due to salinity and turbidity led to adaptations of Asaphus genus Russian Ordovician Trilobites (see figure below). Asaphus expansus branched into two Asaphidae lines of decent, one ultimately leading to Asaphus kowalewski with high eyestalks, and the other branching into two lines, one leading to Asaphus plautini with its large, sharp genal spines genal, and the other leading to another sequence of ever higher eye stalks in Asaphus kotlukovi, then Asaphus punctatus, followed by Asaphus intermedius and finally Asaphus convincens. These observed evolutionary trends are supported by a century of cladistics research that document about two million years of adaptive radiation within the Asery horizon that is more than 50 feet think. As with the examples above, lines of descent can be traced from the ancestors on lower horizons (Wolchow and Kundra), to descendants in the upper horizons (Lasnamjagi and Llandeilo), as shown in the figure below (you can follow some hot spots in the figure).

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