acomplia canada
acomplia canada
Phyllocerida
Systematics
- Class:
- Subclass:
- Superorder: Neoammonoidea
- Order: Phyllocerida
The Phyllocerida, sometimes known as the Phylloceratida or as the suborder Phyllocerina, is a small but persitant stock of neoammonoids, characterized by phlloid saddle endings in the suture, that gave rise to all post Triassic ammonoids. Phylloceratids first appeared in the late Scythian (Lower Triassic) with the Ussuritidae, probably derived from the Dieneroceratidae.
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The Ussuritidae gave rise to the Discophyllitidae at the beginning of the Late Triassic (Carnian), but continued to the end of the period. The Discophyllitidae, which also continued well into the Raetian, give rise to the mostly Jurassic and Cretaceous Phylloceratidae, which forms the bulk of the order. The Ussuritidae or Discophyllitidae also gave rise to the Lytocerida which is the source of most of the Jurassic ammonitids
The Phylloceratidae may have given rise to the Juraphyllitidae, a small family confined to the Lower Jurassic, although the Juraphyllitidae may have evolved separately from the Discophyllitidae, and to certain of the Ammonitida. Otherwise the Phylloceratidae are the only phylloceratids of the post Triassic. The Phylloceratidae gave rise to the Psiloceratidae (Psilocerataceae, Ammonitida) near the beginning of the Jurassic and to the Desmoceratidae (Desmocerataceae) in the Lower Cretaceous (Valanginian) which is the root stock for the principal Cretaceous ammonitids
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The Ussuritidae are evolute with rounded venters and little or no ornamentation. Sutures have primitive, monophyllic saddle endings. The Ussuritidae are also known as the Monophyllitidae.
The Discophyllitidae are similar in form to the Ussuritidae but have diphyllic or triphllic endings to the principal saddles.
The Phylloceratidae are characterized by very thin, smooth, involute shells, usually without ribbing, and in many with fine growth lines. Sutures are complex with major and minor branches of saddles with double, tripple, and even quadruple phylloid and spatulate endings. Contains two subfamilies, the Phylloceratinae without flares and usually without constrictions, and the Calliphylloceratinae regularly with constrictions or flares, or both.
The Juraphyllitidae are compressed, evolute, with a modified body chamber that usually have coarse ventral ribbing. A few genera are more involute, but still compressed. The first lateral saddles are diphyllic, the rest diphyllic or triphyllic.
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- Arkell et al, Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L. R.C. Moore,(ed) 1957.
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