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Keywords:

  • Ammonoidea;
  • Early Ontogeny;
  • Middle Jurassic

In two genera of Callovian Ammonitina of distinct superfamilies, the juvenile shell displays a tuberculate micro-ornament in addition to growth lines. In contrast to the circular micro-tubercles of the ammonitella shell, post-embryonic tubercles are oval to longish in outline. They are arranged in rows running parallel to the growth lines in Kosmoceras (Spinikosmoceras) and cross the growth lines in Binatisphinctes.