Juvenile forms tend to be more evolute with more of the inner whorls showing, whereas mature forms tend to be more involute with outer whorls more strongly embracing.
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Mojvaroceras is a tainoderatid genus, like Metacoceras and its direct evolutionary descendant, differing in being slightly more involute and having a lobe on the inner, dorsal, side. It is known from Triassic sediments in Eurasia and western North America.
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Fissilobiceras is a smooth, compressed, involute ammonite from the lower Middle Jurassic of Europe, named by Buchman in 1919. It is assigned to the hildoceratoid family, Hammatoceratidae. Fissilobiceras is similar to Shirbuirnia, except primarily for being more involute and having complex sutures. More of the inner whorls show in Shirbuirnia and its sutures are simple.
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It is more involute than its predecessor C. exaratum and has higher whorls. Sloping umbilical wall is forming a funnel shaped umbilicus and also a more compressed whorl section. Keel is strong. Nearly all ribs are single and they are of falcoid shape.. They are weak to moderate on microconchs, but stronger in middle growth stage of macroconchs.
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It is more involute than Cleviceras exaratum and Eleganticeras elegantulum, but as it is evolved directly from C. exaratum, there exists some transitional specimens. Also, C. exaratum has vertical, or undercut umbilical walls, while C. elegans has them bevelled, or sloping. C. elegans also has weaker and more striate ribs at sizes below 30mm diameter. Then, ribbing is the same.
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Alocolytoceratinae is a subfamily of lytoceratids that comprises genera characterized by many deep constrictions in the shell resulting in capricorn- like (goat's horm) ornamention, especially in the middle whorls, but becoming smooth and more involute in the outer whorls. Saddle endings in the suture tend to be phylloid, (leaf-like). Alcolytocerainae includes Alocolytoceras, Lobolytoceras, Pachylytocras, and Pleurolytoceras, which are mostly from the Toarcian. One genus, Pachylotoceras, extends into the lower Bajocian.
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Juraphyllitidae is a family of Lower Triassic phylloceratin ammonites from Europe, North Africa, and Asia characterized by narrow, evolutely coiled shells, usually with coarse ventral ribbing on the body chamber. The first lateral saddles in the suture are diphyllic, with two terminal branches, others exposed sutural saddles are diphyllic or triphyllic, those covered by successive whorls being monophyllic. A few genera are more involute, with successive whorls partially embracing the flanks of the previous. All are compressed and a few lack ribbing.
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The Hoplitidae is a family of Cretaceous ammonites that lived during the middle of the period from the late Aptian to the Cenomanian. They are part of the superfamily Hoplitoidea. Members of the Hoplitidae are typically evolute, with inner whorls exposed, although some are more involute, and are commonly stout and strongly ribbed, with pronounced tubercles. The Hoplitidae are thought to be derived from the U Aptian -M Albian Uligella of the Desmoceratidae, or some related form and have been divided into three subfamilies.
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The last three genera are from the Triassic, none having crossed from the Permian. Grypoceras, given simply a Triassic, is like Domatoceras but tending to be more involute and to have more rounded ventral shoulders. Menuthionautilus from the Lower Triassic has a rapidly expanding, smooth involute shell with a deep dorsal impression, broadly convex flanks and rounded venter, suture with a shallow ventral lobe and siphuncle positioned against the venter. Gryponautilus from the Upper Triassic is broadly involute with a narrowly rounded, keel-like venter at maturity and shallow ventral and lateral lobes in the suture.
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