| Measurements | D mm | H/D | T/D | O/D | H/T | Ribs |
|---|---|---|---|---|---|---|
| CP-22 Prins | 52 | 0.50 | 0.32 | 0.17 | 1.58 | 34 |
| Holotype (m) | 68 | 0.48 | 0.28 | 0.19 | 1.73 | 40 |
| CP-10 (M) | 75 | 0.49 | 0.31 | 0.20 | 1.61 | 40 |
| CP-124 (M) | 101 | 0.49 | 0.30 | 0.19 | 1.63 | smooth |
| CP-140 (M) | 155 | 0.46 | 0.26 | 0.22 | 1.76 | 45 |
| Age | Origin |
|---|---|
|
A. besairiei Malagasy zone Lower Albian |
Ambatolafia Boeny Region Madagascar |
Description. Magnificent discoid ammonite with its pearly test, whorls 60% covered, and one quarter of whorl of body chamber. The unfigured side is polished. Lanceolate cross-section with slightly convex flanks that diverge up to the inner third, then flatten and converge towards a narrow, arched venter. The umbilicus has a straight wall at 80° and an angular edge. Very blunt, proverse, and falcate ribs gradually arise, more or less near the umbilical margin. Some shorter ribs begin at mid-flank, and the bifurcations typical of juveniles are no longer present. Seven broad, weak constrictions are followed by a stronger rib originating at the umbilical margin. The 45 ribs, similar at the top of flanks, disappear on venter, as do the constrictions. The image on the right shows the last septum on the polished face, with a deep, asymmetrical first lateral lobe L1, with 3 strong branches (the venter is on the right).
Remarks. During growth, the whorl section becomes higher, the umbilicus opens slightly, the whorls overlap less, the number of ribs increases, but above all, the ornamentation fades. The species then resembles a Beudanticeras, but the latter are smooth at this diameter or have a few regularly spaced ribs and thin constrictions, whereas the flanks of Aioloceras remain slightly wavy along the spire, with weak constrictions here and there.