Parastrenoceras
Encyclopedia
Parastrenoceras is an extinct genus from the ammonoid cephalopod order Ammonitida
, included in the family Spiroceratidae that lived during the Bajocian
stage of the early Middle Jurassic.
Shells of Parastrenoceras are strongly evolute with a subrectangular to subcircular whorl section, generally prominent ribbing, and two rows of tubercles on either side located ventrally and ventrolaterally.
Parastrenoceras is found immediately above Subcollina
in Oaxaca, Mexico and may be descended directly from it. The two agree in the coiling, cross section of the inner whorls, and zigzag pattern of the secondary ribs. Parastrenoceras differs in having two rows of tubercles per side, rather than one, and that the primary ribs on the outer whorls may slope dorso-ventrally forward. Parastrenoceras is also closely related to Spiroceras which, except for its uncoiling, shares many of the same features.
Ammonitida
The Ammonitida is an order of more highly evolved ammonoid cephalopods from the Jurassic and Cretaceous time periods, commonly with intricate ammonitic sutures....
, included in the family Spiroceratidae that lived during the Bajocian
Bajocian
In the geologic timescale, the Bajocian is an age or stage in the Middle Jurassic. It lasted from approximately 171.6 Ma to around 167.7 Ma . The Bajocian age succeeds the Aalenian age and precedes the Bathonian age....
stage of the early Middle Jurassic.
Shells of Parastrenoceras are strongly evolute with a subrectangular to subcircular whorl section, generally prominent ribbing, and two rows of tubercles on either side located ventrally and ventrolaterally.
Parastrenoceras is found immediately above Subcollina
Subcollina
Subcollina is an evolute to serpenticonic stephanoceratacean ammonite from the Middle Jurassic of Mexico, placed in the family Spiroceratidae....
in Oaxaca, Mexico and may be descended directly from it. The two agree in the coiling, cross section of the inner whorls, and zigzag pattern of the secondary ribs. Parastrenoceras differs in having two rows of tubercles per side, rather than one, and that the primary ribs on the outer whorls may slope dorso-ventrally forward. Parastrenoceras is also closely related to Spiroceras which, except for its uncoiling, shares many of the same features.