The Graciloceratidae is a family of nautiloidcephalopods from the Middle and Upper Ordovician belonging to the Oncocerida, characterized by exogastric cyrtocones that expand slightly or moderately and have thin walled, orthochoanitic marginal or subventral, tubular siphuncles (Sweet 1964).
The Graciloceratidae was proposed by Rousseau Flower in 1950 and at that time placed in the Basslerocerida which has since been abandoned. It is now assigned to the Oncocerida (Sweet 1964).
Phylogenyedit
The Graciloceratidae are most likely derived from the Bassleroceratidae (Flower 1950) from which they differ primarily in having thin rather than thick connecting rings. They are also the most likely source for the Oncoceratidae, Tripteroceratidae, and Valcouroceratidae (Flower 1950).
Included generaedit
The Graciloceratidae contains five known genera, four of which are briefly described in the Treatise Part K, Nautiloidea-Oncocerida. The fifth and last listed was named in 2009. They are as follows with their originators:
Graciloceras Flower 1943: slender, compressed, regularly expanding, body chamber much longer than phragmocone; septa very close spaced, siphuncle small, subventral; M-U Ord, NAm. (Sweet K383)
EorizocerasFlower 1943: rapidly expanding, apically curved, adorally straight, faintly compressed with ovoid cross section; sutures straight, slightly oblique; exterior with transverse bands and fine longitudinal markings; no hyponomic sinus; siphuncle small, ventral. M Ord NAm. (Sweet K383)
Piersaloceras Teichert 1930: like Graciloceras but larger, not distinctly compressed, siphuncle well removed from venter, surface with weak longitudinal ribs crossed by thick, ripple-shaped fluttings. U Ord E Eur. (Sweet K383)
Ringoceras Strand 1934: small, strongly curved, depressed; surface with longitudinal ribs and fine, transverse striae; siphuncle subventral; U Ord N Eur. (Sweet K383)&
Kundoceras Kröger 2009: a graciloceratid from the Middle Ordovician of the Baltic region (Kröger, Zhang, and Isakar. 2009)
Referencesedit
Flower,R.H 1950 in Flower and Kummel, A Classification of the Nautiloidea, Journal of Paleontology, Vol 24, no.5, pp604–616, Sept 1950
Sweet. W.C 1964; Nautiloidea-Oncocerida; Treatise on Invertebrate Paleontology Part K Nautiloidea; Geological Society of America and University of Kansas press, Teichert & Moore (eds)
B. Kröger, Y. Zhang, and M. Isakar. 2009. Discosorids and Oncocerids (Cephalopoda) of the Middle Ordovician Kunda and Aseri Regional Stages of Baltoscandia and the early evolution of these groups.
January 01, 1970
graciloceratidae, family, nautiloid, cephalopods, from, middle, upper, ordovician, belonging, oncocerida, characterized, exogastric, cyrtocones, that, expand, slightly, moderately, have, thin, walled, orthochoanitic, marginal, subventral, tubular, siphuncles, . The Graciloceratidae is a family of nautiloid cephalopods from the Middle and Upper Ordovician belonging to the Oncocerida characterized by exogastric cyrtocones that expand slightly or moderately and have thin walled orthochoanitic marginal or subventral tubular siphuncles Sweet 1964 GraciloceratidaeTemporal range M U Ordovician Scientific classification Domain Eukaryota Kingdom Animalia Phylum Mollusca Class Cephalopoda Subclass Nautiloidea Order Oncocerida Family GraciloceratidaeFlower 1950 The Graciloceratidae was proposed by Rousseau Flower in 1950 and at that time placed in the Basslerocerida which has since been abandoned It is now assigned to the Oncocerida Sweet 1964 Phylogeny editThe Graciloceratidae are most likely derived from the Bassleroceratidae Flower 1950 from which they differ primarily in having thin rather than thick connecting rings They are also the most likely source for the Oncoceratidae Tripteroceratidae and Valcouroceratidae Flower 1950 Included genera editThe Graciloceratidae contains five known genera four of which are briefly described in the Treatise Part K Nautiloidea Oncocerida The fifth and last listed was named in 2009 They are as follows with their originators Graciloceras Flower 1943 slender compressed regularly expanding body chamber much longer than phragmocone septa very close spaced siphuncle small subventral M U Ord NAm Sweet K383 EorizocerasFlower 1943 rapidly expanding apically curved adorally straight faintly compressed with ovoid cross section sutures straight slightly oblique exterior with transverse bands and fine longitudinal markings no hyponomic sinus siphuncle small ventral M Ord NAm Sweet K383 Piersaloceras Teichert 1930 like Graciloceras but larger not distinctly compressed siphuncle well removed from venter surface with weak longitudinal ribs crossed by thick ripple shaped fluttings U Ord E Eur Sweet K383 Ringoceras Strand 1934 small strongly curved depressed surface with longitudinal ribs and fine transverse striae siphuncle subventral U Ord N Eur Sweet K383 amp Kundoceras Kroger 2009 a graciloceratid from the Middle Ordovician of the Baltic region Kroger Zhang and Isakar 2009 References editFlower R H 1950 in Flower and Kummel A Classification of the Nautiloidea Journal of Paleontology Vol 24 no 5 pp604 616 Sept 1950 Sweet W C 1964 Nautiloidea Oncocerida Treatise on Invertebrate Paleontology Part K Nautiloidea Geological Society of America and University of Kansas press Teichert amp Moore eds B Kroger Y Zhang and M Isakar 2009 Discosorids and Oncocerids Cephalopoda of the Middle Ordovician Kunda and Aseri Regional Stages of Baltoscandia and the early evolution of these groups Retrieved from https en wikipedia org w index php title Graciloceratidae amp oldid 1166001488, wikipedia, wiki, book, books, library,
