Ecologically distinct silurian (Pridoli) ostracod faunas from central Spain
Gutiérrez-Marco, Juan Carlos
Siveter, David J.
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For several decadas now, the Silurian myodocope ostracod fauna has been recognized as the first planktonic component of the group. Although the colonization event during the middle Silurian (Wenlock-Ludlow) is becoming well documented all around the world, the evolution of this fauna during the late Silurian (Pridoli) still remains unstudied. Here we describe, for the first time, two ecologically distinct myodocope ostracod faunas from the same horizon in the late Pridoli (possibly Istrograptus transgrediens Biozone) of central Spain (Alcaracejos, Córdoba district). The first fauna comes from altered black shales and comprises five myodocope species associated with orthoconic cephalopods and bivalves. The second fauna was recovered from large dark-reddish calcareous nodules containing five myodocope species associated with the planktonic crinoid Scyphocrinites elegans, orthoconic cephalopods, phyllocarids and bivalves. Although the shales and nodules share two myodocopes species, these two faunas seem to have had diferent ecologies, with the shales` association representing the background planktonic fauna, while the nodules` association would have lived in the vicinity of the Scyphocrinites` floating islands. These two faunas may have been living in different parts of the water column.