''Macroloxoceras'' is a large pseuorthocerid from the upper

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

of Central

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

and Southern

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

with features resembling those found in actinocerids.Macroloxoceras, a Devonian Homeomorph of the Actinoceratida, part II Memoir 2, Studies of the Actinoceatidae by Rousseau H Flower. New Mexico Bureau of Mines and Mineral Resources, Socorro NM 1957 Pseudorthocerids and actinocerids (respectively Pseuorthocerida and Actinocerida) are extinct nautiloid

cephalopods A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

, generally with long straight shells and expanded

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

segments filled with organic deposits.

Morphologic description

''Macroloxoceras'' has an orthconic shell with a strongly depressed cross section and markedly flattened venter. Sutures have broad ventral lobes but are otherwise straight and transverse. The siphuncle is ventral of the center; composed of broadly expanded segments with a spheroidal outline. Septal necks are cytochoantic. Connecting rings are thin and make contact over a wide area on the previous septa at their adapical ends. Endosiphuncular deposits are fairly ubiquitous, begin at the septal openings and grow mostly forward to connect with the next in the anterior part of the following segment. Cavities left in the segments are connected to the rings by two series of radial canals; one at the anterior end of the segment near the end of the septal neck; the other starting in the middle, curving back and ending about where the connecting rings makes contact with the previous

septum In biology, a septum (Latin language, Latin for ''something that encloses''; septa) is a wall, dividing a Body cavity, cavity or structure into smaller ones. A cavity or structure divided in this way may be referred to as septate. Examples Hum ...

. Cameral deposits are well developed.Nautiloidea-Orthocerida by Walter C Sweet,

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

Part K Mollusca 3, R.C Moore (ed) 1964

Taxonomy

''Macroloxoceras'', named and described by

Rousseau H. Flower Rousseau Hayner Flower (1913–1988) was an extremely prolific 20th century paleontologist, known for his eccentric personality. Career Although trained as an entomologist, and a specialist in dragonflies and orthopterans, Flower began study ...

in 1957, is included in the Pseudorthocerid family Pseudactinoceratidae and is placed in the subfamily Macroloxoceratinae, named by him for this genus. Flower in 1957 designated the Pseuorthoceratidae as a family in the Michelinoceratida, more commonly known as the Orthocerida. Two species have been identified, the genotype ''Macroloxoceras magnum'' from the Upper Devonian Chaffe

Limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

near Glenwood Springs, Colorado and ''Macroloxoceras minor'' from the upper 20 ft of the Pecha Shale near Santa Rita, New Mexico. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

of ''M. magnum'' is a long section of the phragmocone with 14 camerae and s short portion of the living chamber, the cross section of which increases from a width of and height of 37mm at the base to a width of and height of about at the anterior end. The chambers increase in length from . Septal openings are 5mm across, rings expand so as segments are at least at their greatest width. Siphunclular deposits are thickest in the posterior part of the segments, become thin in the anterior part where they connect with the next deposit forward. Radial canals are as described for the genus. The holotype of ''M. minor'' is a portion of a phragmocone with a natural horizontal section of the siphuncle with the ventral portion remaining and dorsal portion removed be erosion. The ''M. magnum'' holotype is deposited with the Paleontological Research Institute while the ''M. minor'' holotype is in the paleontology collection of the New Mexico Museum of Natural History and Science, transferred from the New Mexico Bureau of Mines and Mineral Resources.

References

{{Taxonbar, from=Q6725400 Nautiloids Taxa named by Rousseau H. Flower