Forresteria

Forresteria is an extinct genus of cephalopod belonging to the subclass Ammonoidea. They flourished during the late Turonian and early Coniacian of the Late Cretaceous,[1] and were global in extent. Forresteria alluaudi and Forresteria hobsoni are considered marker fossils for the lower Coniacian in the American West.

Forresteria
Temporal range: Turonian - Coniacian
Fossil of Forresteria species. Coniacian of Madagascar
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: †Ammonoidea
Order: †Ammonitida
Family: †Collignoniceratidae
Subfamily: †Barroisiceratinae
Genus: †Forresteria
Reeside, 1932
Species

See text

Description

Although the whorl section and ornament of Forresteria are variable, it is easily distinguished from Barroisiceras by the presence of mid-lateral tubercles on the inner whorls, which later disappear or fuse with either umbilical or ventrolateral tubercles. Four subgenera are recognized [2]

  • F. (Forresteria): Whorl section moderately to very inflated. Mid-lateral tubercles fuse with ventrolateral.
  • F. (Reesideoceras): Whorl section less inflated than with F. (Forresteria). Mid-lateral tubercles fuse with the umbilical. Keel disappears on outer whorl leaving venter flat or concave, bordered by ventrolateral clavi.
  • F. (Harleites): Shell compressed, with high keel and steep umbilical wall. Early whorls have weak umbilical, strong mid-lateral, and fine, feeble ventrolateral tubercles.
  • F. (Zumpangoceras): Inclusion doubtful. Known only from crushed specimens from Mexico. Mid lateral tubercle strengthens with age.

Species

species in Forresteria include:

  • Forresteria alluaudi (Boule, Lemoine and Thévenin, 1907)
  • Forresteria brancoi
  • Forresteria hobsoni
  • Forresteria neo-mexica
  • Forresteria petrocoriensis (Coquand, 1859)
  • Forresteria peruana

Forresteria was named for Robert Forrester of Salt Lake City, Utah.[1]

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References
  1. Cobban, William A. et al (2006) "A USGS Zonal Table for the Upper Cretaceous Middle Cenomanian-Maastrichtian of the Western Interior of the United States Based on Ammonites, Inoceramids, and Radiometric Ages" USGS (Open-File Report 2006–1250)
  2. W.J Arkell et al., 1957 Mesozoic Ammonidea. Treatise on Invertebrate Paleontology, Part L Ammonoidea.


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