The Lowoceratidae is a small family of
discosorids, early
nautiloid cephalopods, from the Middle
Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
in which the characteristic bullette is found only in early growth stages. Lowoceratids were first found in Southampton Island in the Canadian arctic.
The Lowoceratidae consists so far of only two genera, ''Lowoceras'' and ''Tuylocras'', named by Foerste and Savage in 1927 and combined by Flower in 1940 as the Lowoceratidae. Both are strongly compressed, exogastric brevicones with the ventral side more narrowly rounded than the dorsal. Shells enlarge moderately to the middle of the mature body chamber, then contract gently toward the aperture. The
siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...
in each is slightly removed from the ventral margin. The siphuncle of ''Tuyloceras'', genotype ''T. percurvatum'', starts off with slender, subquadrate segments with thick rings and swollen bullettes, but later in life the segments become expanded, rings thinner, and bullettes simple and unswollen. ''Lowoceras'', genotype ''L. southamptonense'', is like Tuylocrdas, but with endocones in the siphuncle like the later ''Discosorus''. (Flower and Teichert 1957, Teichert 1964)
The Lowoceratidae are derived from the
Westonoceratidae (Teichert 1964), most likely from ''Faberoceras'', by the suppression of bullettes in the later growth stages. The
Discosoridae
Discosoridae comprise a family of endogastric discosorids, (Cephalopoda, Nautiloidea), with endocones in the siphuncle, ranging from the Middle Silurian to Middle Devonian.
Shell morphology
The shell in the Discosoridae is conical, expanding va ...
are their likely descendants.
References
* Curt Teichert,C, 1964. Nautiloidea -Discosorida;
Treatise on Invertebrate Paleontology, Vol.K,(K320-K325 & K334).
* Flower,R.H.& Teichcert,C., 1957. The Cephalopod Order Discosorida;University of Kansas Paleontological Contributions,Mollusca, Article 6.
{{Taxonbar, from=Q6694131
Discosorida
Silurian first appearances
Silurian extinctions