A "counterweight mechanism" in Hettangian ammonites?

• Autorzy: Longridge L. , Smith P.
• Konferencja: International Congress on the Jurassic System (7 ; 06-18.09.2006 ; Kraków, Poland)
• Języki publikacji: EN

Abstrakty

EN

In most ammonites the siphuncle runs ventrally down the centre of the shell. However, many Hettangian taxa have a siphuncle that is displaced from the midline of the venter accompanied by an asymmetric septal suture line. The ventral lobe is shifted to one side of the whorl where the suture becomes simplified. The ammonites almost became extinct at the end of the Triassic and a single group became the rootstock of the subsequent adaptive radiation. The offset siphuncle is already prevalent in several of the earliest Hettangian genera and by the Late Hettangian, it is widespread throughout two of the three superfamilies. The displacement of the tissue and blood filled siphuncle would have affected the position of the shell’s centre of mass. In order for the ammonite animal to remain vertical in the water column, a "counterweight" system may have been developed. We use computer modeling and data on shell structure to examine this question.

Słowa kluczowe

EN

counterweight mechanism; ammonites; Hettangian; siphuncle; suture line asymmetry

• Wydawca: Państwowy Instytut Geologiczny - Państwowy Instytut Badawczy
• Czasopismo: Volumina Jurassica
• Rocznik: 2006
• Tom: Vol. 4, no. 1
• Strony: 239--239

Twórcy

autor

Longridge L.

autor

Smith P.

• Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, V6T 1Z4, Canada,