Temporal range: M-U Triassic
The Syringonautilidae comprise the last of the Trigonocerataceae and are the source for the Nautilaceae which continued the Nautiloidea through the Mesozoic and into the Cenozoic right down to the recent. The Syringonautilidae, itself, is a strictly Triassic family, derived early in the Triassic from the Grypoceratidae. (Kummel 1964)
The Syringonautilidae are characterized by generally envolute shells -early whorls are in view- with rounded to sagitate whorl sections and smooth surfaces, except for growth lines and fine lirae in some forms. The siphuncle is variable in position, the suture is variably sinuous. (Kummel 1964,K437)
Five genera are described in the Treatise, Syringonautilus, Clymenonautilus, Juvavionautilus, Oxynautilus, and Syringoceras. Syringonautilus and Syringoceras are known from both the Middle and Upper Triassic; Clymenonautilus, Juvavionautilus, and Oxynautilus only from the Upper Triassic. (Kummel 1964. K439-K440)
Syringonautilus (K438) which has been found in the Alps, on Spitsbergen, in India and Japan has a rapidly expanding evolute shell with a perforate umbilicus and suboval whorl section. The suture has a faint ventral saddle and shallow lateral lobes. The siphuncle is subcentral. The surface is ornamented with fine lirae. Syringoceras (K440), found in Europe, on the island of Timur in Indonesia, and in western North America (Calif and Nev) is like Syringonautilus except that the siphuncle is near marginal.
Clymenonautilus (K439), first of the strictly Upper Triassic genera, is evolute with a perforate umbilicus and deep dorsal impression when the whorl envelops a third of the previous. The whorl section is higher than wide with flattened flanks and rounded ventral and umbilical shoulders. The suture is transverse across the venter and has deep, tongue-like lobes on either side. The inner whorls over covered with fine lirae, the outer ones are smooth. The position of the siphuncle is unknown. Clymenoceras comes from Europe.
Juvavionautilus (K439) has a widely umbilicate, slowely expanding, evolte,perforate shell in which the flanks converge on a rounded to flattened venter so that the maximum width is just central of the umbilical shoulders. The suture includes a ventral saddle and broad lateral lobes. In some there is a secondary ventral lobe. The siphuncle is subcentral. Juvavionautilus comes form Europe and Timur.
Oxynautilus( K440) differs from the rest in that it has an involute, compressed lentucualr shell with a narrow or acure (angular) venter which may or may not have a keel. The whorl section is much higher than wide with the maximum width slightly ventral of the umbilical shoulders. The suture is sinuous, including a narrowly rounded to angular ventral saddle and broad lateral lobes. The siphuncle is subcentral. Oxynautilus has been found in Europe in the Alps and in California in North America.
- Kummel,B.1964. Nautiloidea-Nautilida, Treatise on Invertebrate Paleontology Part K, Teichert and Moore (eds) Geological Society of America and University of Kansas Press. pp K437 -K440)