Amphitomariidae is an extinct family of ammonoid cephalopods belonging to the order Anarcestida. This family is known exclusively from the Devonian period, specifically ranging from the Early Devonian (Emsian stage) to the Middle Devonian (Givetian stage).
Members of Amphitomariidae are characterized by their distinctive shell morphology. Their shells are typically discoidal, meaning they are flattened and disc-shaped, with a relatively narrow umbilicus (the central depression of the coiled shell). The coiling is generally involute to convolute, meaning the outer whorls largely overlap or completely cover the inner whorls. The venter (the outer rim of the shell) is often narrowly rounded. Sutures (the lines formed where septa meet the inner shell wall) are generally goniatitic, displaying simple lobes and saddles. The overall shell form suggests they were likely nektonic (free-swimming) organisms, possibly adapted for life in open marine environments.
Fossils of Amphitomariidae have been found in various Devonian marine strata across the globe, indicating a relatively widespread distribution during their existence. Their study contributes to the understanding of ammonoid evolution and paleobiodiversity during the Devonian, a period of significant diversification for early ammonoids.
Key genera associated with this family include Amphitoma and other related forms.