Lowoceratidae
Encyclopedia
The Lowoceratidae is a small family of discosorids
, early nautiloid cephalopods, from the Middle Silurian
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
in each is slightly removed from the ventral margin. The siphuncle of Tuyloceras, genotype T. percurvatum, starts of with slender, subquadrate segments with thick rings and swolen 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 are their likely descendants.
Discosorida
Discosorida is a unique order of cephalopods that lived from the beginning of the Middle Ordovician, through the Silurian, and into the Devonian. Discosorids are unique in the structure and formation of the siphuncle, the tube that runs through and connects the chambers in cephalopods, which unlike...
, early nautiloid cephalopods, from the Middle Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
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
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 Spirula...
in each is slightly removed from the ventral margin. The siphuncle of Tuyloceras, genotype T. percurvatum, starts of with slender, subquadrate segments with thick rings and swolen 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
Westonoceratidae
Westonoceratidae are exogastric, mostly compressed, Discosorida of moderate size from the Middle Ordovician to the Lower Silurian.The siphuncle is typically close to the convexly curved outer margin of the phragmocone -the chambered part of the shell- taken to be ventral but may be more central in...
(Teichert 1964), most likely from Faberoceras, by the suppression of bullettes in the later growth stages. The Discosoridae are their likely descendants.