phylloceratid

fossil ammonite

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July 23, 2026

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The term "phylloceratid" refers to an ammonite belonging to the genus Phylloceras or the family Phylloceratidae. Phylloceras itself is a genus of smooth, involute, and compressed ammonites characterized by complex sutures. These ammonites first appeared in the Triassic period and are believed to be ancestral to most Jurassic and Cretaceous ammonites.12

Ammonoids, including phylloceratids, were extinct cephalopods related to the modern nautilus. They are commonly found as fossils in marine rocks from the Devonian to the Cretaceous periods. Ammonoids possessed shells that provided protection, support, and aided in buoyancy. They are distinguished by their complex suture patterns where internal walls meet the outer shell. Ammonoids are valuable as index fossils due to their wide distribution, rapid evolution, and recognizable features.3

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Triassic Period
Invertebrates
…more complex suture lines, the phylloceratids, also arose in the Early Triassic. They are regarded as the earliest true ammonites and gave rise to all post-Triassic ammonites, even though Triassic ammonoids as a whole almost became extinct at the end of the period.
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…more complex suture lines, the phylloceratids, also arose in the Early Triassic. They are regarded as the earliest true ammonites and gave rise to all post-Triassic ammonites, even though Triassic ammonoids as a whole almost became extinct at the end of the period.
Read More