Abstract Klug, 2001, p.215:

    Whorl expansion rates of six representative ammonoid genera from late Emsian and
    Eifelian strata of Morocco were calculated for each whorl.  The corresponding body
    chamber lengths and the orientations of the apertures were computed based on these
    values.  The resulting body chamber length and orientation of the aperture graphs were
    compared with other conch features, ecology of Recent cephalopods, and sedimentolo-
    gical data of the host rocks in the Tafilalt (eastern Anti-Atlas, Morocco).  A subdivision
    of the ontogeny of these ammonoids was achieved comprising the early and late ein-
    bryonic periods, the juvenile period, the preadult, and the adult growth period.  All
    growth periods are defined by specific changes in growth, conch morphology, and
    mode of tife.  According to this reconstruction, hatchlings were probably already cap-
    able of active movements.  Differentiation in two main modes of life of the examined
    taxa occurred in the late juvenile er early preadult period. As preadult animals, most of
    the Mimagoniatitoidea md Agoniatitoidea became active swimmers (Nektonic),
    whereas the representatives of the Anarcestoidea were capable of slow movements only
    (Planktonic).  As adults, most representatives of the three superfamilies had an approxi-
    mately horizontally oriented aperture, allowing active swimming and possibly active
    choice of spawning sites.  Additionally, the new amonoid taxon Rherisites tuba gen.
    nov., sp. nov. from the late Emsian is introduced. [Ammonoidea, Emsian, Eifelian,
    Morocco, ontogeny, palaeoecology.]