PHYLLOCERAS (Oxfordiense medio, Jurásico sup.)

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Phylloceras (Oxfordian, Middle Jurassic, approximately 155 million years). Sierra de Cazorla (Jaén) Class Cephalopoda, Subclass Ammonoidea, Order Ammonitida, Family Phylloceratidae The phylloceratids were involuted ammonoids with relatively flat shells, lacking ornamentation, and only occasionally displaying growth lines. The sutural lines (intersection between the outer shell and septa) are particularly sinuous, which has been interpreted as a reinforcement of the carapace against implosion when reaching deep zones. This group of ammonoids may have performed migrations related to day-night cycles in the water column like many modern cephalopods. Phylloceratids are found in rocks representing marine platforms to oceanic environments. This specimen, which is fragmented, clearly shows the septa and sedimentary filling of the chambers. CEACTierra-UJA Institute of Gneiss Studies. Projects 2018