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Ordovician nautiloids of Tasmania

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Stait, Bryan Alan (1981) Ordovician nautiloids of Tasmania. PhD thesis, University of Tasmania.

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Abstract

Of the 57 species of nautiloids known in Tasmania 26 are newly
described and there are 17 new genera and one new family.

The nautiloids in the Ordovician of Tasmania are divided into
six biostratigraphic assemblages. The Piloceras-Machuroceras assemblage
is Late Canadian in age and occurs at Adamsfieid in the Florentine
Valley.
It is composed of Pycnoceras adamsense n.sp., Machuroceras
excavatwn, M. steanei, Suecoceras robustum, Piloceras tasmaniense,
Metamanchuroceras wadeae n.gen.,n.sp.,and Allocotoceras insigne.

The Whiterock Wutinoceras-Adamsoceras assemblage occurs in northern and
western Tasmania and the Florentine Valley. It contains Wutinoceras
paucicubiculatwn, W. multicubiculatum, Adamsoceras johnstoni, Karmbergoceras
paucicubiculatum n.gen.,n.sp., and Endoceratidae n.gen.,n.sp. The
Discoceras-Gorbyoceras assemblage is widespread in strata of Chazy to
Blackriver age in Tasmania.
It contains Mysterioceras australe, Gorbyoceras
settlementense n.sp., Fitzgeraldoceras juneese n.~e~.,n.sp.,
Standardoceras burretti n.gen.,n.sp.,Orthoceras sp., Discoceras idaense,
Beloitoceras sp., Centrocyrtocerina frizonense n.gen.,n.sp., Armenoceras
cox•betti n. sp ., Ormocerina asymmetrica n. gen., n. sp., Paramadiganella
banksi n.gen.,n.sp., Florentinoceras calveri n.gen.,n.sp., Anmoceras
lauriei n.gen.,n.sp., Octa,ceras uniquum n.gen.,n.sp., Felixoceras
curtainense n. gen., n. sp ., and Probotryceras u.iestfieldense n. gen., n. sp ..
The Tasmanoceras-Hecatoceras-Gouldoceras assemblage is the most widespread,
occurring throughout Tasmania in the Early Trenton. It contains
Anaspyroceras? anzaas, Discoceras reidi n.sp., Beloitoceras kirtoni,
Mia~oceras bubsense n.sp., Zeehanoceras teicherti n.gen.,n.sp., Tasmanoceras
zeehanense, T. pagei n.sp., Hecatoceras longinquwn, Gouldoceras
synchonena, G. obliquum, G. benjaminense n.sp .. The Gordonoceras assemblage
is of uncertain age, probably Eden, and occurs in the Florentine
Valley and the Gor~on River. It contains only one species Gordonoceras bondi.
The Westfieldoceras assemblage is Maysville in age and is only found in the Florentine Valley. It contains Westfieldoceras taylori n.gen.,n.sp.,
Tigeroceras florentinense n.gen.,n.sp., Armenoceras? sp., and Gouldoceratidae,
n.gen.,n.sp.. Stromatoceras eximium, Ephippiorthoceras decorwn,Sinoceras? sp., Belo-Z:toceras? molense n.sp., and Centrocy11 tocerz.'.na
sharplesi n.gen.,n.sp., cannot be assigned to an assemblage. The number
of endemic genera in the Ordovician of Tasmania increases from a relatively
low number in the Late-Early Ordovician to a very high number in
the Middle and Late Ordovician.
An origin for the Discosorida in the Ellesmeroceratida is suggested
by the simple two-layered connecting rings present in the Gouldoceratidae
(n.fam., Discosorida). The Gouldoceratidae evolved from the Central
Australian genus Madiganella along two different trends. The first
trend is towards more orthochoanitic septal necks and a relative increase
in the size of the siphuncle. The second trend is towards more cyrtochoanitic
septal necks and for a change in the slope of the siphuncular
segments. Armenoceras corbetti has dorso-ventrally differentiated
adnation similar to the Wutinoceratidae and supports an origin in that
family for the Armenoceratidae. Centrocyrtocerina is a gyroconic
cyrtocerinid which evolved from the Late Canadian Eothinoceras through
Tangshanoceras. Kal'l1ibergoceras is an unusual member of the Endoceratidae
as it has two endosiphotubes adorally forming a divided endosiphocone,
the phylogenetic affinities of this genus are unclear.
The shell structure is preserved in some specimens of nautiloids
from Tasmania. They show that fossil nautiloids had a three-layered
shell similar to that in Nautilus except that the oldest specimens known
have only two-layers, suggesting that primitively nautiloids had only
two layers and that the third (inner) layer evolved later.

Item Type: Thesis (PhD)
Keywords: Nautiloidea, Fossil
Copyright Holders: The Author
Copyright Information:

Copyright the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s). 1981.

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1982. Bibliography: l. 255-262

Date Deposited: 03 Feb 2015 03:24
Last Modified: 11 Mar 2016 05:56
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