Porpoceras (Buchman, 1911) is a genus of ammonite that lived during the early and middle Toarcian stage of the Early Jurassic. We see members of this genus from the uppermost part of the Serpentinum Zone to Variabilis Subzone. These beauties are found in Europe, Asia, North America and South America.
Ammonites belonging to this genus have evolute shells, with compressed to depressed whorl section. The flanks are slightly convex and the venter has been low. The whorl section is sub-rectangular.
The rib is pronounced and somewhat fibulate on the inner whorls — just wee nodes here — and tuberculate to spined on the ventrolateral shoulder. It differs from Peronoceras by not having a compressed whorl section and regular nodes or fibulation. Catacoeloceras is also similar, but it has regular ventrolateral tubercles and is missing the classic nodes or fibulation of his cousins.
This specimen hails from southern France near the Rhône, one of the major rivers of Europe. It has twice the average water level of the Loire and is fed by the Rhône Glacier in the Swiss Alps at the far eastern end of the Swiss canton of Valais then passes through Lake Geneva before running through southeastern France. This 10 cm specimen was prepared by the supremely talented José Juárez Ruiz