New Zealand Journal of Geology and Geophysics abstracts
Jaws of Triassic ammonoids from New Zealand
Neil H. Landman
Division of Paleontology (Invertebrates)
American Museum of Natural History
79th Street and Central Park West
New York, NY 10024, USA
landman@amnh.org
Andrew Grebneff
Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand
andrew.grebneff@stonebow.otago.ac.nz
Abstract Cephalopod jaws have been recovered from
the Etalian (Middle Triassic = Anisian–Ladinian) of New Zealand. The
jaws are found as isolated elements in the Tilson Siltstone near Kaka
Point, southeast Otago. The structures are interpreted as jaws of
ceratitid and phylloceratid ammonoids. Most of the jaws are small,
<10 mm in length, but two specimens are much larger:
c. 35 mm in length. The lower jaws conform to the published
descriptions of anaptychus type jaws. Each jaw is convex on the ventral
side and terminates in a projected apex. The surface is covered with
regularly spaced ridges that parallel the posterior margin. The inner
lamella is preserved near the anterior margin and in areas where the
outer lamella has eroded away. The upper jaws are rarer, with their
inner lamella ending in a bilobate posterior margin. The lower jaws are
similar to those of Paleozoic ammonoids and contrast with those of the
Ancyloceratina and most of the Ammonitina, which are characterised by a
midline flange with a central groove and a pair of calcareous plates
(aptychi), and the Lytoceratina, which bear calcareous deposits at the
apex.
Keywords ammonites; jaws; anaptychus; Tilson
Siltstone; New Zealand; Middle Triassic
G05010; Received 21 February 2005; accepted 5 September 2005; Online
publication date 3 March 2006
New Zealand Journal of Geology & Geophysics, 2006, Vol. 49:
121–129
0028–8306/06/4901–0121 © The Royal Society of New Zealand 2006
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