Reudemannoceratidae
Encyclopedia
The Reudemannoceratidae are the ancestral and most primitive of the Discosorida
, an order of cephalopods from the early Paleozoic
. The Reudemannoceratidae produced generally medium sized endogastric and almost straight shells with the siphuncle
slightly ventral from the center.
, North American Whiterock stage, (since replaced by the ICS
Dapingian), and are restricted to the lower part of that series. (the middle Ordovician). Their origin is unknown. The siphuncles in early members contain features in the early growth stages reminiscent of the siphuncular bulbs found the archaic Plectronoceratae
of the Late Cambrian. (Flower and Teichert 1957) but so far no unambiguous Lower Ordovician intermediaries have been found.
in eastern North America. Madiganella, named by Teichert and Glenister in 1952, comes from central Australia
.
Reudemannoceras is described (Flower and Teichert 1957) as having a somewhat compressed endogastric shell, such that the width is greater that the height, with the venter slightly flattened. Sutures are closely spaced and slope forward from venter to dorsum with the obliquity increasing as growth progressed. The early part of the shell is essentially straight, but afterwords expands and is notably curved. The early segments in the siphuncle (Techert 1964) are bulb shaped and the septal necks are short. In the later part of the shell she segments are expanded and septal necks become recumbent. The connecting rings are thick and have the zoning characteristic of the earlier Discosorids with well-developed bullettes.
Franklinoceras (Teichert 1964) is similar to Reudemannocereras, except that the shell is compressed and the sutures are straight.
Madiganella has a large, slender, straight or nearly straight shell (Teichert 1964) with a siphuncle composed of broad, expanded segments and short, strongly recurved necks. Growth lines indicate a shallow hyponomic sinus.
through Ulrichoceras (Teichert 1964) as a result of an evolutionary ventral shift of the siphuncle and the development of large, inflated bullettes. Ulrichoceras is the probable ancestor of the Westonoceratidae
as well. Reudemannoceras is also thought to have given rise (Teichert 1964) to Madiganella by an evolutionary straightening of the shell which by the subsequent development of T-shaped constricted apertures gave rise to the Mandaloceratidae
. Franklinoceras seems to be an offshoot of Reudemanoceras with no progeny. .
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...
, an order of cephalopods from the early Paleozoic
Paleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
. The Reudemannoceratidae produced generally medium sized endogastric and almost straight shells with 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...
slightly ventral from the center.
Derivation
The Reudemannoceratidae first appeared at the beginning of the Middle OrdovicianOrdovician
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...
, North American Whiterock stage, (since replaced by the ICS
ICS
-Communications and technology:* Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy* Industrial Control System* Information and Computer Science, the combined field of informatics and computing...
Dapingian), and are restricted to the lower part of that series. (the middle Ordovician). Their origin is unknown. The siphuncles in early members contain features in the early growth stages reminiscent of the siphuncular bulbs found the archaic Plectronoceratae
Plectronocerida
Plectronocerida is a primitive order from which subsequent cephalopod orders are ultimately derived.-Occurrence:Plectronoceratids are known from the Upper Cambrian of China and North America...
of the Late Cambrian. (Flower and Teichert 1957) but so far no unambiguous Lower Ordovician intermediaries have been found.
Characters
Reudemannoceratids are characterized by having short septal necks in the juvenile portion of the siphuncle, toward the apex of the shell, which later in life grow folded back along the back side of the septa in the characteristic fashion of the Discosorida. The connecting ring is bowed out into the camerae and is divided into the characteristic zones, the vinculum, granular zone, conchiolinous (or chitinous) zone offset by amorphous bands, and the layered bullette attached to the previous septal neck. (Flower and Teichert 1957, Teichert 1964)Genera
The Reucenammanoceratidae contain three genera (Teichert 1964). They are Reudemannoceras, Franklinoceras, and Madiganella. Reudemannoceras and Franklinoceras, named by Flower in 1940 and 1957, are found the Champlain ValleyChamplain Valley
The Champlain Valley is a region of the United States around Lake Champlain in Vermont and New York extending slightly into Quebec, Canada as part of the St. Lawrence River drainage basin drained northward by the Richelieu River into the St...
in eastern North America. Madiganella, named by Teichert and Glenister in 1952, comes from central Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
.
Reudemannoceras is described (Flower and Teichert 1957) as having a somewhat compressed endogastric shell, such that the width is greater that the height, with the venter slightly flattened. Sutures are closely spaced and slope forward from venter to dorsum with the obliquity increasing as growth progressed. The early part of the shell is essentially straight, but afterwords expands and is notably curved. The early segments in the siphuncle (Techert 1964) are bulb shaped and the septal necks are short. In the later part of the shell she segments are expanded and septal necks become recumbent. The connecting rings are thick and have the zoning characteristic of the earlier Discosorids with well-developed bullettes.
Franklinoceras (Teichert 1964) is similar to Reudemannocereras, except that the shell is compressed and the sutures are straight.
Madiganella has a large, slender, straight or nearly straight shell (Teichert 1964) with a siphuncle composed of broad, expanded segments and short, strongly recurved necks. Growth lines indicate a shallow hyponomic sinus.
Evolution and Phylogeny
Reudemannoceras gave rise to the CyrtogomphoceratidaeCyrtogomphoceratidae
The Cyrtogomphoceratidae is a family in the cephalopod order Discosorida that comprises genera commonly with compressed, endogastrically curved shells. Siphuncles lie close to the venral side, segments are broadly inflated, connecting rings thick and apically expanded thick bullettes. Chambers are...
through Ulrichoceras (Teichert 1964) as a result of an evolutionary ventral shift of the siphuncle and the development of large, inflated bullettes. Ulrichoceras is the probable ancestor of 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...
as well. Reudemannoceras is also thought to have given rise (Teichert 1964) to Madiganella by an evolutionary straightening of the shell which by the subsequent development of T-shaped constricted apertures gave rise to the Mandaloceratidae
Mandaloceratidae
Mandaloceratidae is a family in the nautiloid cephalopod order, Discosorida, from the Middle and Upper Silurian characterized by essentially straight, breviconic shells, most with a faintly exogastric shape produced by the profile of the body chamber...
. Franklinoceras seems to be an offshoot of Reudemanoceras with no progeny. .
Ecology and lifestyle
Reudemannoceratids were probably lived on or near the sea floor. Endogastric Reudemannoceras and Franklinoceras are likely to have carried their shells high and to the back, aperture facing downward, as they probed the sea bed for prey. The more advanced and slightly later Madiganella may have may have been a fair swimmer, as indicated by the hyponomic sinus,and may have been an active stalker with a horizontal orientation.References
- Flower,R.H.and Teichert,C.,1957. The Cephalopod Order Discosorida; University of Kansas Paleontological Contributions, Mollusca, Article 6.
- Teichert,C.,1964. Nautiloidea -Discosorida; 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...
, Vol. K, (K320-k328)