Ontogeny of Upper Cretaceous (Turonian-Santonian) scaphitid ammonites from the Western Interior of North America : systematics, developmental patterns, and life history. Bulletin of the AMNH ; v. 185, article 2 ; Ontogeny of scaphitid ammonites
You can manage bookmarks using lists, please log in to your user account for this.
Media type:
E-Book;
Text
Title:
Ontogeny of Upper Cretaceous (Turonian-Santonian) scaphitid ammonites from the Western Interior of North America : systematics, developmental patterns, and life history. Bulletin of the AMNH ; v. 185, article 2 ; Ontogeny of scaphitid ammonites
Contributor:
Landman, Neil H.
[Author]
imprint:
[New York] : American Museum of Natural History, 1987
Footnote:
Diese Datenquelle enthält auch Bestandsnachweise, die nicht zu einem Volltext führen.
Description:
p. 118-241 : ill., map ; 26 cm. ; Includes bibliographical references (p. 234-241). ; "Scaphites are a group of late Cretaceous heteromorphic ammonites in which the final body chamber partially uncoils, thereby marking the attainment of the adult stage. This distinctive change in shape permits unequivocal separation of variation due to developmental stage from phenotypic variation among adults. In the Western Interior of North America, scaphites are represented by a wide diversity of endemic species. Many of these species are abundant and well preserved and, therefore, are especially suitable for a detailed investigation of ontogenetic development. I studied the ontogeny of several species of Turonian-Santonian scaphites in the genera Scaphites, Clioscaphites and Pteroscaphites, utilizing both whole fossils and polished sections. The study of their ontogeny bears on the questions of scaphite systematics and morphological development, and ammonite life history in general. The initial whorls of scaphites, as in other ammonites, consist of a bulbous protoconch and part of a planispiral whorl (referred to as the ammonitella). The ammonitella displays a uniform tuberculate micro-ornamentation extending 0.75 whorls to a depression (primary constriction) after which growth lines appear. The shell wall is prismatic in microstructure and nacre first appears at the constriction where it forms an internal pad (primary varix). These morphological observations support a scheme of direct development in which the constriction marks the aperture of the embryonic shell. Preserved ammonitellas of Scaphites ferronensis and Baculites cf. B. asper, B. codyensis suggest that hatching may have occurred after the development of the Proseptum. In scaphites, the proseptum displays a unique necklike attachment that appears as a superimposed saddle on the prosuture. The caecum and its prosiphonal attachment are similar among all the species studied. The diameter of the embryonic shell averages 700 [micrometers] and ranges from ...