Holmiceras
Encyclopedia
Holmiceras is one of two ancestral lituitids
from the late Early Ordovician
(Arenigian). The other being Ancistroceras
.
Holmiceras begins with about 1.5 to 2 loosely coiled whorls followed by a rapidly expanding orthocone, much like Ancistroceras except for the apical whorls and that Holmiceras is known only from the late Early Ordovician whereas Ancestroceras extends through the middle of the period.
Holmiceras may have given rise to Angelinoceras
which begins with an expanding open spiral.
Lituitidae
The Lituitidae is a family of evolved tarphycerids characterized by a long orthoconic section that follows a coiled juvenile portion at the apex, along with a generally tubular siphuncle, which like that of the barrandeocerids is composed of thin connecting rings.-Taxonomic Position:Flower and...
from the late Early Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
(Arenigian). The other being Ancistroceras
Ancistroceras
Ancistroceras is one of the two ancestral lituitids from the late Early Ordovician . The other being Holmiceras.The shell is weakly annulate, starts off with 1.5 to 2 contiguous or slightly separated whorls followed by a rapidly expanding orthocone with an apical angle of about 30 deg...
.
Holmiceras begins with about 1.5 to 2 loosely coiled whorls followed by a rapidly expanding orthocone, much like Ancistroceras except for the apical whorls and that Holmiceras is known only from the late Early Ordovician whereas Ancestroceras extends through the middle of the period.
Holmiceras may have given rise to Angelinoceras
Angelinoceras
Angelinoceras is a lituitid from the Middle Ordovician that starts off with a open spiral of about 1.5 strongly compressed whorls followed by an orthoconic section that continues to expand for a length about equal to the diameter of the coiled portion before retaining a more or less consistent...
which begins with an expanding open spiral.
References
- Flower, R. H. 1950. A Classification of the Nautiloidia. Jour Paleontology, V.24, N.5, pp 604–616, Sept.
- Furnish & Glenister, 1964. Nautiloidea -Tarphycerida. Treatise on Invertebrate PaleontologyTreatise on Invertebrate PaleontologyThe Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...
Part K, Mollusca 3 ...Nautiloidea