''Microbaltoceras'' is an extinct genus of the cephalopod family

Baltoceratidae Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, exist ...

that lived in what would be North America during the

Early Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

. It was named by

Rousseau 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 stud ...

(1964) and assigned by him to the Baltoceratidae. The type species is ''Microbaltoceras minore'' which was found in the Threadgill Member of the Tanyard Formation in

Gillespie County Gillespie County is a County (United States), county located on the Edwards Plateau in the U.S. state of Texas. As of the 2020 United States Census, 2020 census, its population was 26,725. The county seat is Fredericksburg, Texas, Fredericksburg ...

, Texas, USA. The shell of ''Microbaltoceras'' is straight (orthconic) and tiny, with the

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 ...

in narrow contact with the inner ventral surface. Its inclusion in the

rather than in the

Ellesmeroceratidae The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the do ...

is based in large part on the lack of observable diaphragms in the siphuncle. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

of ''Microbaltoceras minore'' is only 10mm long, essentially all

phragmocone The phragmocone is the chambered portion of the shell of a cephalopod. It is divided by septa into camerae. In most nautiloids and ammonoids, the phragmocone is a long, straight, curved, or coiled structure, in which the camarae are linked by a ...

References

*R. H. Flower. (1964). The Nautiloid Order Ellesmeroceratida (Cephalopoda). Memoir 12, New Mexico Bureau of Mines and Mineral Resources, Socorro, NM, {{Taxonbar, from=Q16977651 Ordovician cephalopods of North America Ordovician cephalopods Taxa named by Rousseau H. Flower Orthocerida Prehistoric cephalopod genera