Lytocerida

From Palaeos.org

Lytocerida

Systematics

• Class: Cephalopoda
• Subclass: Ammonoidea
• Superorder: Neoammonoidea
• Order: Lytocerida

The Lytocerida (Lytoceratina in the Treatise) are loosely coiled, evolute neoammonoids further characterized by having round whorls commonly ornamented with flares and with growth lines and by sutures with few but very complex elements with mosslike saddle endings. Aptici where found are single valved.

The Lytocerida are derived from either the Ussuitidae or Discophyllitidae of the Phyllocerida, or perhaps both. The earliest, from the Lower Jurassic, the Pleuracanthitidae and Ectocentritidae, retain some characters of the Phyllocerida especially in the somewhat phylloid saddle endings.

The Lytocerida contains the superfamily Lytocerataceae and three, the Ancylocerataceae, Turrilitaceae, and Scaphitaceae which have been reassigned to the Ancylocerida, but which probably should be thought of as separately derived lytocerids. The Lytocerataceae includes the Lytoceratidae which is the dominant family of the order and a number of smaller families. The taxonomy of the Lytocerataceae according to Arkell et al 1957 follows

• Order Lytocerida

• Superfamily Lytocerataceae
  • Fam. Lytoceratidae (type)
  • Fam. Arcuceratidae
  • Fam. Derolytoceratidae
  • Fam. Ectocentritidae
  • Fam. Nannolytoceratidae
  • Fam. Pleuracanthitidae
  • Fam. Protetragonitidae
  • Fam. Spiroceratidae
  • Fam. Tetragonitidae

The Pleuracanthitidae, Ectocentritidae (see above), and Derolytoceratidae are basal families from the Lower Jurassic. The Arcuceratidae, Nannolytoceratidae, and Spiroceratidae are Jurassic derivatives of the Lytoceratidae with very short to moderate ranges. The Protetragonitidae (also uppermost Jurassic) and Tetragonitidae are Cretaceous derivatives of the Lytoceratidae with rather long ranges. The Lytoceratidae has the longest range of all, from the Lower Jurassic Sinemurian to the middle of the Cretaceous, Cenomainian. Only the Tetragonitidae in the Lytocerataceae extend further, to the end of the (Cret) period.

For the Ancylocerataceae, Turrilitaceae, and Scaphitaceae see Ancylocerida

References

• Arkell, et al,1957. Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L. Geological Society of America.

JM 8/08/10