| Measurements | D mm | H/D | T/D | O/D | H/T |
|---|---|---|---|---|---|
| CP-144 | 31 | 0.48 | 0.53 | 0.15 | 0.91 |
| CP-53 | 51.4 | 0.45 | 0.41 | 0.21 | 1.08 |
| CP-13 | 67.5 | 0.50 | 0.49 | 0.16 | 1.03 |
| CP-143 | 90 | 0.47 | 0.47 | 0.21 | 0.99 |
| CP-443 | 100.1 | 0.46 | 0.43 | ? | 1.06 |
| Age | Origin |
|---|---|
|
Lower Albian Aioloceras besairiei Malagasy zone |
Ambatolafia Boeny Region Madagascar |
Description. Ammonite with a partially preserved pearly test and a body chamber on the last half-whorl, very involute, with a broad, inverted U-shaped cross-section. The umbilicus is very narrow and deep, with a vertical wall connected to the flanks by a narrowly rounded shoulder. The internal mold shows seven shallow, sigmoid constrictions crossing the venter with a broad, rounded proverse sinus. On the test, these are filled with ridges, visible mainly on the outer half of the flanks and venter. Between these ridges, the test is adorned with fine, dense growth lines of the same course.
Sutures and variants. The sutures have bifid saddles of decreasing height and a siphonal lobe as deep as the first lateral lobe, which is trifid and symmetrical. Our specimens correspond to the most widespread variant, D. latidorsatum sensu stricto, defined by an H/T ratio between 0.90 and 1.10 (Collignon, 1949). The internal mold generally bears constrictions, up to 10 per whorl in thicker forms. Compressed forms, on the other hand, have fewer and less pronounced constrictions, or even none at all. According to Andreas Richter (www.leitfossil.de), these would be microconchs.
Age and distribution. Long known as Latidorsella latidorsatum, it is the only species of the genus Desmoceras in France. It is variable, cosmopolitan, and long-lived: in Europe, from the Middle Albian to the Upper Cenomanian. It can reach 20 cm in diameter. In the Aube region, only small pyritic nuclei (see Michelin, 1838) are found from the beginning of Albian up to the cristatum zone (base of Upper Albian), with a peak in the benettianus zone.