Ancyloceratidae

Australiceras sp., in the Houston Museum of Natural Science.

Belongs within: Aptychophora.

The Ancyloceratidae are a group of ammonites known from the Lower Cretaceous. They are commonly heteromorphic, though some derived forms reverted to a more standard tight coil.

Characters (from Wright et al. 1996): Either coiled in a loose or tight, more or less equiangular spiral (criocone) or with an initial spire followed by curved or straight shaft and terminal hook (ancyloceratoid); sometimes with phylogenetic tendency to tighter, normal ammonitic coiling. Whorl section ranging from circular to square or polygonal; tending to develop strong, periodic ribs with umbilical, lateral, and ventrolateral spines, separated by few to many, fine, untuberculate ribs. Ornament rarely constant through growth. Probably strongly dimorphic throughout, but presumed microconchs rarely matched with macroconchs. Sutures florid, with trifid lobes or simplifying.

<==Ancyloceratidae [Ancylocerataceae] EK02
    |  i. s.: Parancyloceras bidentatum W69, K79
    |         Menuthiocrioceras W69
    |         Pedioceras W69
    |--Lithancylus W69
    `--+--+--Colchidites shaoriensis W69
       |  `--Turkmeniceras turkmenicum W69
       |--Ancyloceras d’Orbigny 1842 W69, EK02 [Ancyloceratinae]
       |    |--A. durrelli K79
       |    |--A. flindersi F71
       |    |--A. innexum K79
       |    `--A. vandenheckii K79
       |--+--Epancyloceras W69
       |  `--Ammonitoceras W69
       |       |--A. tovilense W69
       |       `--A. ucetiae W69
       `--+--Tropaeum W69
          |    |  i. s.: T. arcticum K79
          |    |         T. australe K79
          |    |         T. jacki K79
          |    |         T. leptum (Etheridge 1909) [=Crioceras leptum] F71
          |    |--T. hillsi W69
          |    `--+--T. bowerbanki W69
          |       `--T. subarcticum W69
          `--Australiceras W69
               |  i. s.: A. gracile F71
               |         A. irregulare [=Crioceras irregulare] F71
               |         A. lampros (Etheridge 1909) [=Crioceras lampros] F71
               |         A. robustum Whitehouse 1926 F71
               |--A. gigas W69
               `--+--A. jacki W69 [=Crioceras jackii F71; incl. Tropaeum undatum F71]
                  `--A. tuberculatum W69

*Type species of generic name indicated

REFERENCES

[EK02] Engeser, T., & H. Keupp. 2002. Phylogeny of the aptychi-possessing Neoammonoidea (Aptychophora nov., Cephalopoda). Lethaia 35: 79–96.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[K79] Kauffman, E. G. 1979. Cretaceous. In: Robison, R. A., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt A. Introduction. Fossilisation (Taphonomy), Biogeography and Biostratigraphy pp. A418–A487. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[W69] Wiedmann, J. 1969. The heteromorphs and ammonoid extinction. Biological Reviews 44: 563–602.

Wright, C. W., J. H. Callomon & M. K. Howarth. 1996. Treatise on Invertebrate Paleontology pt L. Mollusca 4, Revised vol. 4. Cretaceous Ammonoidea. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).