Abstract
A new ammonite ( Fuciniceras paradoxus) is described here. This Lower Domerian species is based on a recently revised collections which came from the Maria Pares section (Rabaçal area, South of Coimbra, Portugal). Curiously, shell of F. paradoxus bears both diagnostic traits for the genus Protogrammoceras SPATH (e.g. acute ogival ventral area) and Fuciniceras HAAS (e.g. angulirursiradiate rib). Thus, the new species can be viewed as a morphological puzzle and as a challenge for taxonomists. The amazing collection of morphological traits previously suspected as highly improbable because of biomechanical constraints (1) confirms the inadequacy of the traditional use of the genera Protogrammoceras and Fuciniceras, (2) refutes the idea of a univocal biomechanic link between the ventral area morphology and the ventral segment of ribs. If this analysis mainly concern the Harpoceratinae subfamily, its generalisation can also be interesting for other ammonites or molluscan groups.
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