Abstract
The phosphatic siphuncle of Bactroceras latisiphonatum Glenister, a Late Ordovician member of the ancestral order of nautiloid cephalopods, displays the outer ‘chalky’ and inner ‘horny’ tubes seen in the aragonitic connecting rings of Recent Nautilus and Carboniferous Orthocerida. The specimens were collected from the Malongulli Formation of central New South Wales. Bactroceras resembles Mesozoic ammonoids in having a marginal phosphatic connecting ring that is partly a product of diagenetic phosphatization. Both the septa and connecting rings were apparently able to resist greater hydrostatic water pressures than other ellesmerocerids and had a potential implosion depth comparable to that of mature Nautilus. The septal necks and siphuncle position resemble the morphology of Bactrites; but it is unlikely that Bactroceras and ‘Eobactrites’ were directly ancestral to bactritoids and ammonoids.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callMore From: Alcheringa: An Australasian Journal of Palaeontology
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
