Macroloxoceras is a large pseuorthocerid

Pseudorthocerida

Pseudorthocerida are generally straight longiconic nautiloids with a subcentral to marginal cyrtochoanitic siphuncle composed of variably expanded segments which may contain internal deposits that may develop into a continuous parietal lining.. Cameral deposits are common and concentrated ventrally...

 from the upper Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 of Central Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

 and Southern New Mexico

New Mexico

New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

 with features resembling those found in
actinocerids

Actinocerida

The Actinocerida comprise an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposits formed within contain a system of radial...

.
Pseudorthocerids and actinocerids (respectively Pseuorthocerida and Actinocerida) are extinct nautiloid cephalopods, generally with long straight shells and expanded 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...

 segments filled with organic deposits.

Morphologic Description

Macroloxoceras has an orthconic shell with a strongly depressed cross section and markedly flattened venter. Suture

Suture

Surgical suture is a medical device used to hold body tissues together after an injury or surgery. It generally consists of a needle with an attached length of thread. A number of different shapes, sizes, and thread materials have been developed over its millennia of history.-History:Through many...

s 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. Cameral deposits are well developed.

Taxonomic Position

Macroloxoceras, named and described by Flower, 1957, is included in the Pseudorthocerid family Pseudactinoceratidae. Flower rather included Macroloxoceras in what he named the Macroloxoceratinae, a subfamily of the Pseuorthoceratidae which then, 1957, was designated a family in the Michelinoceratida, more commonly known as the Orthocerida.

Species

Two species have been identified, the genotype Macroloxoceras magnum from the Upper Devonian Chaffe Limestone near Glenwood Springs, Colorado and Macroloxoceras minor from the upper 20 ft of the Pecha Shale near Santa Rita, New Mexico.

The holotype of M magnum is a 240 mm 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 56 mm and height of 37 at the base to a width of 100 mm and height of about 42 mm at the anterior end. The chambers increase in length from 10 to 19 mm. Septal openings are 5 mm across, rings expand so as segments are at least 16 mm at their greatest width. Siphunclular depostis are thickest in the posterior part of the segments, become thin in the anteror part when they connect with the next depostis forward. Radial canals are as described for the genus.

The holotype of M minor is a portion of a phragmocone with a natural horizonal section of the siphuncle with the ventral portion remaining and dorsal portion removed be erosion.

The holotype

Holotype

A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...

of Macroloxoceras magnum is deposited with the Paleontological Research Institute. The holotype of M minor 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