Discophyllitidae
Encyclopedia
Discophyllitidae are discoidal, generally evolute Phylloceratina
from the Upper Triassic, derived from the Ussuritidae
, in which the principal saddles of the suture have bifurcated or trifurcated endings, described as being di- or triphyllic. Discophyllitid shells are rather similar to those of the ancestral Ussuritidae and are distinguished primarily by the more complex suture. The Discophyllitidae provided the source for the Jurassic Phylloceratidae
and Juraphyllitidae
. Four genera are recognized and described.
Discophyllites and Rhacophyllites have their beginnings in the early Late Triassic. Both are found in Europe, the Himalayas, and on Timur; Discophyllites in California and Alaska as well. Discophyllites is the more primitive and ancestral genus. Rhacophyllites is slightly more evolved with its more developed suture.
Tragorhacoceras and Trachyphyllites are known from the middle Late Triassic, Tragorhacoceras from the Alps and Sicily, Trachyphyllites from the island of Timur. Both result from further, but different, evolutionary developments within the Discophyllitidae.
Phylloceratina
The Phyllocertina comprise a suborder of ammonoid cephalopods, belonging to the Ammonitida, whose range extends from the Lower Triassic to the Upper Cretaceous...
from the Upper Triassic, derived from the Ussuritidae
Ussuritidae
Ussuritidae are ancestral, Triassic, Phylloceratina characterized by generally smooth, discoidal, evolute shells with rounded venters and little or no ornamentation and by sutures with primitive monophyllitic saddles with a single terminal branch or leaflet....
, in which the principal saddles of the suture have bifurcated or trifurcated endings, described as being di- or triphyllic. Discophyllitid shells are rather similar to those of the ancestral Ussuritidae and are distinguished primarily by the more complex suture. The Discophyllitidae provided the source for the Jurassic Phylloceratidae
Phylloceratidae
Phylloceratidae is the predominant family of the Phylloceratina with some 15 or more genera found in rocks ranging from the Lower Jurassic to the Upper Cretaceous. Members of the Phylloceratidae are characterized by smooth, involute shells with very thin walls. Many are covered with fine growth...
and Juraphyllitidae
Juraphyllitidae
Juraphyllitidae is a family of Lower Triassic phylloceratin ammonites from Europe, North Africa, and Asia characterized by narrow, evolutely coiled shells, usually with coarse ventral ribbing on the body chamber...
. Four genera are recognized and described.
Discophyllitid Genera
- Discophyllites: Discophyllitids in which the first lateral saddle of the suture is asymmetrically monophyllic, like those of the Ussuritidae. The remaining are characteristic of the family.
- Rhacophyllites: Discophyllitidae in which the first lateral saddle of the suture is diphyllic and adjacent lateral saddles are diphyllic or triphillic.
- Tragorhacoceras: Discophyllitidae with peripheral ribs on the outer whorl and with large leaflets in the sutural saddles.
- Trachyphyllites: a discophyllitid with sigmoidal growth lines and about six ribs or flares per whorl; suture less phylloid than in other genera of the family.
Discophyllites and Rhacophyllites have their beginnings in the early Late Triassic. Both are found in Europe, the Himalayas, and on Timur; Discophyllites in California and Alaska as well. Discophyllites is the more primitive and ancestral genus. Rhacophyllites is slightly more evolved with its more developed suture.
Tragorhacoceras and Trachyphyllites are known from the middle Late Triassic, Tragorhacoceras from the Alps and Sicily, Trachyphyllites from the island of Timur. Both result from further, but different, evolutionary developments within the Discophyllitidae.