Hematitida is a group of coleoid cephalopods known from the early Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 Period. They are the oldest definite coleoids, although there are controversial claims for even older coleoids from the 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...

. Fossil hematitidans have so far been found only in Arkansas

Arkansas

Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...

 and Utah

Utah

Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

 of the USA. The only family described so far is Hematitidae.

Characteristics

Some features shared by hematitidans include

• a short rostrum, made of aragonite
  Aragonite
  Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...
  
   and organic
  Organic matter
  Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...
  
   material, and bearing ridges
• a short living chamber, only 1.5 to 2 times the length of the last chamber of the phragmocone
  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 siphuncle which determines buoyancy by means of gas...
  
  
• a spherical protoconch
  Protoconch
  A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...
  
  
• a narrow, straight phragmocone
  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 siphuncle which determines buoyancy by means of gas...
  
  
• a multi-layered conotheca - the outer wall of the phragmocone
• a narrow, ventral 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...
  
  

Classification

The classification for this group comes from Doguzhaeva et al. 2003

Order Hematitida Doguzhaeva, Mapes, & Mutvei, 2002

• Family Hematitidae Gustomesov 1976
  • Hematites Flower & Gordon 1959 - type genus
  • Bactritimimus Flower & Gordon, 1959
  • Paleoconus Flower & Gordon, 1959