First record of Late Callovian to Early Oxfordian heteromorph ammonites

The outstanding discovery of two heteromorph ammonites in Late Callovian and Early Oxfordian deposits, where such ammonites were deemed absent, substantially reduce the interval without heteromorph ammonite known into the Jurassic. A new species is described for the Early Oxfordian: Acuariceras acucostis sp. nov.; the Late Callovian Parapatoceras cf. tuberculatum is also studied. These latter expands our knowledge of the latest Parapatoceratinae and complete their stratigraphic distribution. The evolution of ornamentation between A. acuarius/Paracuariceras incisum and A. acucostis sp. nov., from which it is derived, tends toward a net reinforcement of the ribs at least on the body chamber. Without the preservation of the suture lines however, it is difficult to know the relationships maintained between the new species and the genera Acuariceras and Paracuariceras. It is not excluded that these two genera, which are distinguished only on the basis of relatively discrete suturing criteria, could be synonymous. (C) 2016 Elsevier Masson SAS. All rights reserved.